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Publisher: Oxford University Press (OUP)
Date: 12-11-2023
Abstract: The WALLABY pilot survey has been conducted using the Australian SKA Pathfinder (ASKAP). The integrated 21-cm H i line spectra are formed in a very different manner compared to usual single-dish spectra Tully–Fisher measurements. It is thus extremely important to ensure that slight differences (e.g. biases due to missing flux) are quantified and understood in order to maximise the use of the large amount of data becoming available soon. This article is based on four fields for which the data are scientifically interesting by themselves. The pilot data discussed here consist of 614 galaxy spectra at a rest wavelength of 21 cm. Of these spectra, 472 are of high enough quality to be used to potentially derive distances using the Tully–Fisher relation. We further restrict the s le to the 251 galaxies whose inclination is sufficiently close to edge-on. For these, we derive Tully–Fisher distances using the deprojected WALLABY velocity widths combined with infrared (WISE W1) magnitudes. The resulting Tully–Fisher distances for the Eridanus, Hydra, Norma, and NGC4636 clusters are 21.5, 53.5, 69.4, and 23.0 Mpc, respectively, with uncertainties of 5–10 per cent, which are better or equivalent to the ones obtained in studies using data obtained with giant single dish telescopes. The pilot survey data show the benefits of WALLABY over previous giant single-dish telescope surveys. WALLABY is expected to detect around half a million galaxies with a mean redshift of $z = 0.05 (200\\, \\mathrm{Mpc})$. This study suggests that about 200 000 Tully–Fisher distances might result from the survey.
Publisher: Cambridge University Press (CUP)
Date: 2005
DOI: 10.1071/AS05030
Abstract: We present the proceedings from a two-day workshop held at Swinburne University on 2005 May 24–25. The workshop participants highlighted current Australian research on both theoretical and observational aspects of galaxy groups. These proceedings include short one-page summaries of a number of the talks presented at the workshop. The talks presented ranged from reconciling N -body simulations with observations, to the Hı content of galaxies in groups and the existence of ‘dark galaxies’. The formation and existence of ultra-compact dwarfs in groups, and a new supergroup in Eridanus were also discussed.
Publisher: American Astronomical Society
Date: 30-11-2010
Publisher: American Astronomical Society
Date: 06-2000
DOI: 10.1086/301374
Publisher: American Astronomical Society
Date: 03-02-2016
Publisher: Springer Netherlands
Date: 2003
Publisher: Oxford University Press (OUP)
Date: 21-06-2017
Publisher: EDP Sciences
Date: 04-2022
DOI: 10.1051/0004-6361/202142048
Abstract: Context. The Shapley Supercluster (⟨ z ⟩≈0.048) contains several tens of gravitationally bound clusters and groups, making it an ideal subject for radio studies of cluster mergers. Aims. We used new high sensitivity radio observations to investigate the less energetic events of mass assembly in the Shapley Supercluster from supercluster down to galactic scales. Methods. We created total intensity images of the full region between A3558 and A3562, from ∼230 to ∼1650 MHz, using ASKAP, MeerKAT and the GMRT, with sensitivities ranging from ∼6 to ∼100 μJy beam −1 . We performed a detailed morphological and spectral study of the extended emission features, complemented with ESO-VST optical imaging and X-ray data from XMM-Newton . Results. We report the first GHz frequency detection of extremely low brightness intercluster diffuse emission on a ∼1 Mpc scale connecting a cluster and a group, namely: A3562 and the group SC 1329–313. It is morphologically similar to the X-ray emission in the region. We also found (1) a radio tail generated by ram pressure stripping in the galaxy SOS 61086 in SC 1329–313 (2) a head-tail radio galaxy, whose tail is broken and culminates in a misaligned bar (3) ultrasteep diffuse emission at the centre of A3558. Finally (4), we confirm the ultra-steep spectrum nature of the radio halo in A3562. Conclusions. Our study strongly supports the scenario of a flyby of SC 1329–313 north of A3562 into the supercluster core. This event perturbed the centre of A3562, leaving traces of this interaction in the form of turbulence between A3562 and SC 1329–313, at the origin of the radio bridge and eventually affecting the evolution of in idual supercluster galaxies by triggering ram pressure stripping. Our work shows that minor mergers can be spectacular and have the potential to generate diffuse radio emission that carries important information on the formation of large-scale structures in the Universe.
Publisher: Oxford University Press (OUP)
Date: 02-03-2012
Publisher: American Astronomical Society
Date: 05-2023
Abstract: We report on the commensal ASKAP detection of a fast radio burst (FRB), FRB 20211127I, and the detection of neutral hydrogen (H i ) emission in the FRB host galaxy, WALLABY J131913–185018 (hereafter W13–18). This collaboration between the CRAFT and WALLABY survey teams marks the fifth, and most distant, FRB host galaxy detected in H i , not including the Milky Way. We find that W13–18 has an H i mass of M HI = 6.5 × 10 9 M ⊙ , an H i -to-stellar mass ratio of 2.17, and coincides with a continuum radio source of flux density at 1.4 GHz of 1.3 mJy. The H i global spectrum of W13–18 appears to be asymmetric, albeit the H i observation has a low signal-to-noise ratio (S/N), and the galaxy itself appears modestly undisturbed. These properties are compared to the early literature of H i emission detected in other FRB hosts to date, where either the H i global spectra were strongly asymmetric, or there were clearly disrupted H i intensity map distributions. W13–18 lacks a sufficient S/N to determine whether it is significantly less asymmetric in its H i distribution than previous ex les of FRB host galaxies. However, there are no strong signs of a major interaction in the optical image of the host galaxy that would stimulate a burst of star formation and hence the production of putative FRB progenitors related to massive stars and their compact remnants.
Publisher: Oxford University Press (OUP)
Date: 30-07-2015
Publisher: Springer Netherlands
Date: 2008
Publisher: American Astronomical Society
Date: 29-10-2018
Publisher: Cambridge University Press (CUP)
Date: 06-2007
DOI: 10.1017/S174392130701438X
Abstract: The Arecibo L-band Feed Array Zone of Avoidance Survey (ALFA ZOA) will map 1350-1800 deg 2 at low Galactic latitude, providing HI spectra for galaxies in regions of the sky where our knowledge of local large scale structure remains incomplete, owing to obscuration from dust and high stellar confusion near the Galactic plane. Because of these effects, a substantial fraction of the galaxies detected in the survey will have no optical or infrared counterparts. However, near infrared follow up observations of ALFA ZOA sources found in regions of lowest obscuration could reveal whether some of these sources could be objects in which little or no star formation has taken place (“dark galaxies”). We present here the results of ALFA ZOA precursor observations on two patches of sky totaling 140 deg 2 (near l = 40°, and l = 192°). We have measured HI parameters for detections from these observations, and cross-correlated with the NASA/IPAC Extragalactic Database (NED). A significant fraction of the objects have never been detected at any wavelength. For those galaxies that have been previously detected, a significant fraction have no previously known redshift, and no previous HI detection.
Publisher: Oxford University Press (OUP)
Date: 11-04-2001
Publisher: Cambridge University Press (CUP)
Date: 2006
DOI: 10.1071/AS05039
Abstract: Four massive, early-type stars, three of which are confirmed binaries, have been observed with the Australia Telescope Compact Array at 1.4, 2.4, 4.8, and 8.6 GHz. The earliest star cataloged so far, HD 93129A, was also observed at 17.8 and 24.5 GHz. Here we present an analysis of the spectra as well as the structure of the stellar systems. All four spectra show clear evidence of non-thermal emission, indicative of a binary system with a colliding wind region. We discuss the magnetic field of the emitting region of HD 93129A and make predictions on the radiation at high energies. Archive X-ray observations towards the target sources are also investigated and interpreted in the light of the non-thermal emission detected.
Publisher: EDP Sciences
Date: 26-10-2010
Publisher: Cambridge University Press (CUP)
Date: 2012
DOI: 10.1071/ASV29N3_PR
Abstract: Large radio surveys such as those proposed for several SKA pathfinder and precursor telescopes require (automated) source-finding algorithms that are highly reliable, complete, and fast. Similarly, sophisticated visualisation tools are needed to explore the resulting survey data together with their multi-wavelength counterparts. In this PASA Special Issue on Source Finding and Visualisation, several advanced source-finding algorithms, including novel methods for radio continuum, polarisation and spectral line surveys are described, tested and compared. The process of finding sources can be considered one of many important steps (e.g., pre-processing, source finding and characterisation, cataloguing ost-processing) in the production of astronomical source catalogues, on which much of the survey science is based. The Australian SKA Pathfinder (ASKAP), equipped with novel Chequerboard phased array feeds, will be a powerful 21-cm survey machine. For the large volumes of ASKAP data, a special version of Duch , called Selavy, is being developed in consultation with the ASKAP survey science teams (Whiting & Humphreys 2012). Extensive testing and comparisons of existing and new source-finding algorithms were carried out for this PASA Special Issue and are presented by Westmeier, Popping & Serra (2012), Westerlund, Harris & Westmeier (2012), Popping et al. (2012), Huynh et al. (2012), Hollitt & Johnston-Hollitt (2012), Walsh et al. (2012), George, Stil & Keller (2012), Marsh & Jarrett (2012), Allison, Sadler & Whiting (2012) and Jurek & Brown (2012). An overview on spectral line source finding and visualisation is given by Koribalski (2012), while Hassan, Fluke & Barnes (2012) look into real-time 3D volume rendering of large (Tbytes) astronomical data cubes.
Publisher: Oxford University Press (OUP)
Date: 28-11-2023
Abstract: We examine the H i gas kinematics of galaxy pairs in two clusters and a group using Australian Square Kilometre Array Pathfinder (ASKAP) WALLABY pilot survey observations. We compare the H i properties of galaxy pair candidates in the Hydra I and Norma clusters, and the NGC 4636 group, with those of non-paired control galaxies selected in the same fields. We perform H i profile decomposition of the s le galaxies using a tool, baygaud, which allows us to deblend a line-of-sight velocity profile with an optimal number of Gaussian components. We construct H i superprofiles of the s le galaxies via stacking of their line profiles after aligning the central velocities. We fit a double Gaussian model to the superprofiles and classify them as kinematically narrow and broad components with respect to their velocity dispersions. Additionally, we investigate the gravitational instability of H i gas discs of the s le galaxies using Toomre Q parameters and H i morphological disturbances. We investigate the effect of the cluster environment on the H i properties of galaxy pairs by iding the cluster environment into three subcluster regions (i.e. outskirts, infalling, and central regions). We find that the denser cluster environment (i.e. infalling and central regions) is likely to impact the H i gas properties of galaxies in a way of decreasing the litude of the kinematically narrow H i gas ($M_{\\rm {narrow}}^{\\rm {H\\, \\small {\\rm I}}}$/$M_{\\rm {total}}^{\\rm {H\\, \\small {\\rm I}}}$), and increasing the Toomre Q values of the infalling and central galaxies. This tendency is likely to be more enhanced for galaxy pairs in the cluster environment.
Publisher: Oxford University Press (OUP)
Date: 29-12-2018
Publisher: Oxford University Press (OUP)
Date: 03-11-2012
Publisher: Oxford University Press (OUP)
Date: 16-02-2018
DOI: 10.1093/MNRAS/STY387
Publisher: Springer Netherlands
Date: 2008
Publisher: Oxford University Press (OUP)
Date: 02-2005
Publisher: EDP Sciences
Date: 08-2021
DOI: 10.1051/0004-6361/202140797
Abstract: Context. Studies of the stellar and the H I gas kinematics in dwarf and low surface brightness (LSB) galaxies are essential for deriving constraints on their dark matter distribution. Moreover, a key component to unveil in the evolution of LSBs is to determine why some of them can be classified as superthin. Aims. We aim to investigate the nature of the proto-typical superthin galaxy Fourcade-Figueroa (FF) to understand the role played by the dark matter halo in forming its superthin shape and to investigate the mechanism that explains the observed disruption in the approaching side of the galaxy. Methods. Combining new H I 21 cm observations obtained with the Giant Metrewave Radio Telescope with archival data from the Australia Telescope Compact Array we were able to obtain sensitive H I observations of the FF galaxy. These data were modelled with a 3D tilted ring model in order to derive the rotation curve and surface brightness density of the neutral hydrogen. We subsequently used this model, combined with a stellar profile from the literature, to derive the radial distribution of the dark matter in the FF galaxy. Additionally, we used a more direct measurement of the vertical H I gas distribution as a function of the galactocentric radius to determine the flaring of the gas disk. Results. For the FF galaxy, the Navarro-Frenk-White dark matter distribution provides the best fit to the observed rotation curve. However, the differences with a pseudo-isothermal halo are small. Both models indicate that the core of the dark matter halo is compact. Even though the FF galaxy classifies as superthin, the gas thickness about the galactic centre exhibits a steep flaring of the gas that agrees with the edge of the stellar disk. In addition, FF is clearly disrupted towards its north-west side, clearly observed at optical and H I wavelengths. As suggested previously in the literature, the compact dark matter halo might be the main cause for the superthin structure of the stellar disk in FF. This idea is strengthened through the detection of the disruption the fact that the galaxy is disturbed also appears to support the idea that it is not isolation that causes its superthin structure.
Publisher: Oxford University Press (OUP)
Date: 02-1999
Publisher: American Astronomical Society
Date: 09-2004
DOI: 10.1086/422923
Publisher: Oxford University Press (OUP)
Date: 12-01-2017
DOI: 10.1093/MNRAS/STX053
Publisher: Oxford University Press (OUP)
Date: 09-11-2012
DOI: 10.1093/MNRAS/STS160
Publisher: Oxford University Press (OUP)
Date: 06-1998
Publisher: Springer Netherlands
Date: 2008
Publisher: Oxford University Press (OUP)
Date: 13-08-2015
Publisher: Oxford University Press (OUP)
Date: 04-2001
Publisher: Oxford University Press (OUP)
Date: 14-08-2017
Publisher: EDP Sciences
Date: 07-2015
Publisher: Springer Netherlands
Date: 2008
Publisher: Oxford University Press (OUP)
Date: 14-05-2021
Abstract: We present results from neutral atomic hydrogen (H i) observations of Hydra I, the first cluster observed by the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) on the Australian Square Kilometre Array Pathfinder. For the first time, we show that WALLABY can reach its final survey sensitivity. Leveraging the sensitivity, spatial resolution, and wide field of view of WALLABY, we identify a galaxy, ESO 501−G075, that lies near the virial radius of Hydra I and displays an H i tail. ESO 501−G075 shows a similar level of morphological asymmetry as another cluster member, which lies near the cluster centre and shows signs of experiencing ram pressure. We investigate possible environmental processes that could be responsible for producing the observed disturbance in the H i morphology of ESO 501−G075. We rule out tidal interactions, as ESO 501−G075 has no nearby neighbours within ∼0.34 Mpc. We use a simple model to determine that ram pressure can remove gas from the disc at radii r ≳ 25 kpc. We conclude that, as ESO 501−G075 has a typical H i mass compared to similar galaxies in the field and its morphology is compatible with a ram pressure scenario, ESO 501−G075 is likely recently infalling into the cluster and in the early stages of experiencing ram pressure.
Publisher: EDP Sciences
Date: 06-2021
DOI: 10.1051/0004-6361/202040260
Abstract: Context. SPT-CL J2106-5844 is among the most massive galaxy clusters at z 1 yet discovered. While initially used in cosmological tests to assess the compatibility with Λ Cold Dark Matter cosmology of such a massive virialized object at this redshift, more recent studies indicate SPT-CL J2106-5844 is undergoing a major merger and is not an isolated system with a singular, well-defined halo. Aims. We use sensitive, high spatial resolution measurements from the Atacama Large Millimeter/Submillimeter Array (ALMA) and Atacama Compact Array (ACA) of the thermal Sunyaev-Zeldovich (SZ) effect to reconstruct the pressure distribution of the intracluster medium in this system. These measurements are coupled with radio observations from the pilot survey for the Evolutionary Map of the Universe, using the Australian Square Kilometre Array Pathfinder (ASKAP), and the Australia Telescope Compact Array (ATCA) to search for diffuse nonthermal emission. Further, to better constrain the thermodynamic structure of the cluster, we complement our analysis with reprocessed archival Chandra observations. Methods. We jointly fit the ALMA and ACA SZ data in uv -space using a Bayesian forward modeling technique. The ASKAP and low-frequency ATCA data are processed and imaged to specifically highlight any potential diffuse radio emission. Results. In the ALMA and ACA SZ data, we reliably identify at high significance two main gas components associated with the mass clumps inferred from weak lensing. Our statistical test excludes at the ∼9.9 σ level the possibility of describing the system with a single SZ component. While the components had been more difficult to identify in the X-ray data alone, we find that the bimodal gas distribution is supported by the X-ray hardness distribution. The EMU radio observations reveal a diffuse radio structure ∼400 kpc in projected extent along the northwest-southeast direction, indicative of strong activity from the active galactic nucleus within the brightest cluster galaxy. Interestingly, a putative optical star-forming filamentary structure detected in the HST image is in an excellent alignment with the radio structure, albeit on a smaller scale.
Publisher: Springer Netherlands
Date: 2008
Publisher: American Astronomical Society
Date: 07-09-2023
Publisher: IOP Publishing
Date: 30-08-2022
Abstract: This paper presents data from a 21 cm H i emission drift scan observation of a field partially covering the NGC 4636 galaxy group with the Five-hundred meter Aperture Radio Telescope (FAST). We construct a pipeline to reduce the data, and use SoFiA for source finding. When not contaminated by Radio Frequency Interference (RFI), the FAST observations are capable of detecting all of the galaxies previously detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey in the same region. Comparing to ALFALFA for the detections in common, the FAST data show consistent integrated spectra when the H i disks are spatially unresolved, and capture more flux when the H i disks are resolved. The FAST data further reveal 10 new detections in the region mutually covered with ALFALFA, and 18 new detections beyond the footprint of ALFALFA. All of the new detections have the matching optical counterparts. For the member galaxies of the NGC 4636 group, the detection limit of FAST is deeper by 0.4 dex in H i mass than that of the ALFALFA data. After correcting for the incompleteness caused by RFI contamination, we show that the H i detection rate of galaxies rises steeply with radius out to the virial radius of the group, and flattens beyond that. We also examine four spatially resolved galaxy systems with potential tidal interaction features in detail. Considering that the data have been taken during the “shared-risk” period before a major source of local RFI was eliminated, the results highlight the power of FAST in detecting extragalactic H i .
Publisher: EDP Sciences
Date: 12-2015
Publisher: Oxford University Press (OUP)
Date: 03-2005
Publisher: Oxford University Press (OUP)
Date: 31-12-2016
Publisher: Oxford University Press (OUP)
Date: 21-03-2013
DOI: 10.1093/MNRAS/STT340
Publisher: Oxford University Press (OUP)
Date: 20-08-2014
Publisher: American Association for the Advancement of Science (AAAS)
Date: 09-08-2019
Abstract: Fast radio bursts (FRBs) are brief radio emissions from distant astronomical sources. Some are known to repeat, but most are single bursts. Nonrepeating FRB observations have had insufficient positional accuracy to localize them to an in idual host galaxy. We report the interferometric localization of the single-pulse FRB 180924 to a position 4 kiloparsecs from the center of a luminous galaxy at redshift 0.3214. The burst has not been observed to repeat. The properties of the burst and its host are markedly different from those of the only other accurately localized FRB source. The integrated electron column density along the line of sight closely matches models of the intergalactic medium, indicating that some FRBs are clean probes of the baryonic component of the cosmic web.
Publisher: Oxford University Press (OUP)
Date: 06-2004
Publisher: Oxford University Press (OUP)
Date: 09-2008
Publisher: Oxford University Press (OUP)
Date: 22-12-2016
Publisher: EDP Sciences
Date: 07-2018
DOI: 10.1051/0004-6361/201732410
Abstract: During pilot observations of the Virgo Environmental Survey Tracing Galaxy Evolution (VESTIGE), a blind narrow-band H α + [NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT, we have observed the spiral galaxy NGC 4254 (M99). Deep H α + [NII] narrow-band and GALEX UV images reveal the presence of 60 compact (70–500 pc radius) star-forming regions up to ≃20 kpc outside the optical disc of the galaxy. These regions are located along a tail of HI gas stripped from the disc of the galaxy after a rapid gravitational encounter with another Virgo cluster member that simulations indicate occurred 280–750 Myr ago. We have combined the VESTIGE data with multifrequency data from the UV to the far-infrared to characterise the stellar populations of these regions and study the star formation process in an extreme environment such as the tails of stripped gas embedded in the hot intracluster medium. The colour, spectral energy distribution (SED), and linear size consistently indicate that these regions are coeval and have been formed after a single burst of star formation that occurred ≲100 Myr ago. These regions might become free floating objects within the cluster potential well, and be the local analogues of compact sources produced after the interaction of gas-rich systems that occurred during the early formation of clusters.
Publisher: EDP Sciences
Date: 07-2015
Publisher: American Association for the Advancement of Science (AAAS)
Date: 25-05-2007
Abstract: Recycled dwarf galaxies can form in the collisional debris of massive galaxies. Theoretical models predict that, contrary to classical galaxies, these recycled galaxies should be free of nonbaryonic dark matter. By analyzing the observed gas kinematics of such recycled galaxies with the help of a numerical model, we demonstrate that they do contain a massive dark component amounting to about twice the visible matter. Staying within the standard cosmological framework, this result most likely indicates the presence of large amounts of unseen, presumably cold, molecular gas. This additional mass should be present in the disks of their progenitor spiral galaxies, accounting for a substantial part of the so-called missing baryons.
Publisher: EDP Sciences
Date: 05-2022
DOI: 10.1051/0004-6361/202141054
Abstract: Context. In the first months after its launch in July 2019, the extended Roentgen Survey with an Imaging Telescope Array (eROSITA) on board Spektrum-Roentgen-Gamma performed long-exposure observations in the regions around supernova (SN) 1987A and super-nova remnant (SNR) N132D in the Large Magellanic Cloud (LMC). Aims. We analysed the distribution and the spectrum of the diffuse X-ray emission in the observed fields to determine the physical properties of the hot phase of the interstellar medium (ISM). Methods. Spectral extraction regions were defined using the Voronoi tessellation method. The spectra were fit with a combination of thermal and non-thermal emission models. The eROSITA data are complemented by newly derived column density maps for the Milky Way and the LMC, 888 MHz radio continuum map from the Australian Square Kilometer Array Pathfinder, and optical images of the Magellanic Cloud Emission Line Survey. Results. We detect significant emission from thermal plasma with kT = 0.2 keV in all the regions. There is also an additional higher- temperature emission component from a plasma with kT ≈ 0.7 keV. The surface brightness of this component is one order of magnitude lower than that of the lower-temperature component. In addition, non-thermal X-ray emission is significantly detected in the superbubble 30 Dor C. The absorbing column density N H in the LMC derived from the analysis of the X-ray spectra taken with eROSITA is consistent with the N H obtained from the emission of the cold medium over the entire area. Neon abundance is enhanced in the regions in and around 30 Dor and SN 1987A, indicating that the ISM has been chemically enriched by the young stellar population. In the centre of 30 Dor, there are two bright extended X-ray sources, which coincide with the stellar cluster RMC 136 and the Wolf-Rayet stars RMC 139 and RMC 140. For both regions the emission is best modelled with a high-temperature ( kT 1 keV) non-equilibrium ionisation plasma emission and a non-thermal component with a photon index of Γ = 1.3. In addition, we detect an extended X-ray source at the position of the optical SNR candidate J0529-7004 with thermal emission, and thus confirm its classification as an SNR. Conclusions. Using data from the early observations of the regions around SN 1987A and SNR N132D with eROSITA we confirm that there is thermal interstellar plasma in the entire observed field. eROSITA with its large field of view and high sensitivity at lower X-ray energies allows us for the first time to carry out a detailed study of the ISM at high energies consistently over a large region in the LMC. We thus measure the properties of the interstellar plasma and the distribution of non-thermal particles and derive the column density of the cold matter on the line of sight.
Publisher: Oxford University Press (OUP)
Date: 10-2005
Publisher: Oxford University Press (OUP)
Date: 08-01-2021
Abstract: We present observations of a region of the Galactic plane taken during the Early Science Program of the Australian Square Kilometre Array Pathfinder (ASKAP). In this context, we observed the scorpio field at 912 MHz with an uncompleted array consisting of 15 commissioned antennas. The resulting map covers a square region of ∼40 deg2, centred on (l, b) = (343.5°, 0.75°), with a synthesized beam of 24 × 21 arcsec2 and a background rms noise of 150–200 μJy beam−1, increasing to 500–600 μJy beam−1 close to the Galactic plane. A total of 3963 radio sources were detected and characterized in the field using the caesar source finder. We obtained differential source counts in agreement with previously published data after correction for source extraction and characterization uncertainties, estimated from simulated data. The ASKAP positional and flux density scale accuracy were also investigated through comparison with previous surveys (MGPS, NVSS) and additional observations of the scorpio field, carried out with ATCA at 2.1 GHz and 10 arcsec spatial resolution. These allowed us to obtain a measurement of the spectral index for a subset of the catalogued sources and an estimated fraction of (at least) 8 per cent of resolved sources in the reported catalogue. We cross-matched our catalogued sources with different astronomical data bases to search for possible counterparts, finding ∼150 associations to known Galactic objects. Finally, we explored a multiparametric approach for classifying previously unreported Galactic sources based on their radio-infrared colours.
Publisher: EDP Sciences
Date: 06-2018
DOI: 10.1051/0004-6361/201732407
Abstract: The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band (NB) Hα +[NII] imaging survey carried out with MegaCam at the Canada–France–Hawaii Telescope. The survey covers the whole Virgo cluster region from its core to one virial radius (104 deg 2 ). The sensitivity of the survey is of f ( Hα ) ~ 4 × 10 −17 erg s −1 cm −2 (5 σ detection limit) for point sources and Σ( Hα ) ~ 2 × 10 −18 erg s −1 cm −2 arcsec −2 (1 σ detection limit at 3 arcsec resolution) for extended sources, making VESTIGE the deepest and largest blind NB survey of a nearby cluster. This paper presents the survey in all its technical aspects, including the survey design, the observing strategy, the achieved sensitivity in both the NB Hα +[NII] and in the broad-band r filter used for the stellar continuum subtraction, the data reduction, calibration, and products, as well as its status after the first observing semester. We briefly describe the Hα properties of galaxies located in a 4 × 1 deg 2 strip in the core of the cluster north of M87, where several extended tails of ionised gas are detected. This paper also lists the main scientific motivations for VESTIGE, which include the study of the effects of the environment on galaxy evolution, the fate of the stripped gas in cluster objects, the star formation process in nearby galaxies of different type and stellar mass, the determination of the Hα luminosity function and of the Hα scaling relations down to ~10 6 M ⊙ stellar mass objects, and the reconstruction of the dynamical structure of the Virgo cluster. This unique set of data will also be used to study the HII luminosity function in hundreds of galaxies, the diffuse Hα +[NII] emission of the Milky Way at high Galactic latitude, and the properties of emission line galaxies at high redshift.
Publisher: American Astronomical Society
Date: 06-09-2012
Publisher: Oxford University Press (OUP)
Date: 18-10-2021
Abstract: We analyse the surface brightness profiles of disc-type galaxies in the Evolution and Assembly of GaLaxies and their Environment (EAGLE) simulations in order to investigate the effects of galaxy mass and environment on galaxy profile types. Following observational works, we classify the simulated galaxies by their disc surface brightness profiles into single exponential (Type I), truncated (Type II), and antitruncated (Type III) profiles. In agreement with previous observation and theoretical work, we find that Type II discs result from truncated star-forming discs that drive radial gradients in the stellar populations. In contrast, Type III profiles result from galaxy mergers, extended star-forming discs or the late formation of a steeper, inner disc. We find that the EAGLE simulations qualitatively reproduce the observed trends found between profile type frequency and galaxy mass, morphology and environment, such as the fraction of Type III galaxies increasing with galaxy mass, and the fraction of Type II galaxies increasing with Hubble type. We investigate the lower incidence of Type II galaxies in galaxy clusters, finding, in a striking similarity to observed galaxies, that almost no S0-like galaxies in clusters have Type II profiles. Similarly, the fraction of Type II profiles for disc-dominated galaxies in clusters is significantly decreased relative to field galaxies. This difference between field and cluster galaxies is driven by star formation quenching. Following the cessation of star formation upon entering a galaxy cluster, the young stellar populations of Type II galaxies simply fade, leaving behind Type I galaxies.
Publisher: Oxford University Press (OUP)
Date: 26-06-2006
Publisher: Oxford University Press (OUP)
Date: 22-02-2018
DOI: 10.1093/MNRAS/STY479
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.41
Abstract: The Rapid ASKAP Continuum Survey (RACS) is the first large-area survey to be conducted with the full 36-antenna Australian Square Kilometre Array Pathfinder (ASKAP) telescope. RACS will provide a shallow model of the ASKAP sky that will aid the calibration of future deep ASKAP surveys. RACS will cover the whole sky visible from the ASKAP site in Western Australia and will cover the full ASKAP band of 700–1800 MHz. The RACS images are generally deeper than the existing NRAO VLA Sky Survey and Sydney University Molonglo Sky Survey radio surveys and have better spatial resolution. All RACS survey products will be public, including radio images (with $\\sim$ 15 arcsec resolution) and catalogues of about three million source components with spectral index and polarisation information. In this paper, we present a description of the RACS survey and the first data release of 903 images covering the sky south of declination $+41^\\circ$ made over a 288-MHz band centred at 887.5 MHz.
Publisher: Oxford University Press (OUP)
Date: 09-08-2021
Abstract: We present observations of the Eridanus supergroup obtained with the Australian Square Kilometre Array Pathfinder (ASKAP) as part of the pre-pilot survey for the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY). The total number of detected H i sources is 55, of which 12 are background galaxies not associated with the Eridanus supergroup. Two massive H i clouds are identified and large H i debris fields are seen in the NGC 1359 interacting galaxy pair, and the face-on spiral galaxy NGC 1385. We describe the data products from the source finding algorithm and present the basic parameters. The presence of distorted H i morphology in all detected galaxies suggests ongoing tidal interactions within the subgroups. The Eridanus group has a large fraction of H i-deficient galaxies as compared to previously studied galaxy groups. These H i-deficient galaxies are not found at the centre of the group. We find that galaxies in the Eridanus supergroup do not follow the general trend of the atomic gas fraction versus stellar mass scaling relation, which indicates that the scaling relation changes with environmental density. In general, the majority of these galaxies are actively forming stars.
Publisher: Oxford University Press (OUP)
Date: 03-2016
DOI: 10.1093/MNRAS/STW186
Publisher: EDP Sciences
Date: 03-08-2009
Publisher: Cambridge University Press (CUP)
Date: 2012
DOI: 10.1071/AS11067
Abstract: The large size of the ASKAP H i surveys DINGO and WALLABY necessitates automated 3D source finding. A performance difference of a few percent corresponds to a significant number of galaxies being detected or undetected. As such, the performance of the automated source finding is of paramount importance to both of these surveys. We have analysed the performance of various source finders to determine which will allow us to meet our survey goals during the DINGO and WALLABY design studies. Here we present a comparison of the performance of five different methods of automated source finding. These source finders are duch , gamma-finder , a cnhi finder , a 2 d –1 d wavelet reconstruction finder and a sigma clipping method ( s + c finder ). Each source finder was applied to the same three-dimensional data cubes containing (a) point sources with a Gaussian velocity profile and (b) spatially extended model-galaxies with inclinations and rotation profiles. We focus on the completeness and reliability of each algorithm when comparing the performance of the different source finders.
Publisher: Oxford University Press (OUP)
Date: 03-2003
Publisher: Cambridge University Press (CUP)
Date: 2012
DOI: 10.1071/AS12030
Abstract: Here I will outline successes and challenges for finding spectral line sources in large data cubes that are dominated by noise. This is a 3D challenge as the sources we wish to catalog are spread over several spatial pixels and spectral channels. While 2D searches can be applied, e.g. channel by channel, optimal searches take into account the 3-dimensional nature of the sources. In this overview I will focus on H i 21-cm spectral line source detection in extragalactic surveys, in particular HIPASS, the H i Parkes All-Sky Survey and WALLABY, the ASKAP H i All-Sky Survey. I use the original HIPASS data to highlight the ersity of spectral signatures of galaxies and gaseous clouds, both in emission and absorption. Among others, I report the discovery of a 680 km s −1 wide H i absorption trough in the megamaser galaxy NGC 5793. Issues such as source confusion and baseline ripples, typically encountered in single-dish H i surveys, are much reduced in interferometric H i surveys. Several large H i emission and absorption surveys are planned for the Australian Square Kilometre Array Pathfinder (ASKAP): here we focus on WALLABY, the 21-cm survey of the sky ( δ + 30° z 0.26) which will take about one year of observing time with ASKAP. Novel phased array feeds (‘radio cameras’) will provide 30 deg 2 instantaneous field-of-view. WALLABY is expected to detect more than 500 000 galaxies, unveil their large-scale structures and cosmological parameters, detect their extended, low-surface-brightness disks as well as gas streams and filaments between galaxies. It is a precursor for future H i surveys with SKA Phase I and II, exploring galaxy formation and evolution. The compilation of highly reliable and complete source catalogs will require sophisticated source-finding algorithms as well as accurate source parametrisation.
Publisher: Oxford University Press (OUP)
Date: 18-10-2012
Publisher: Oxford University Press (OUP)
Date: 06-2004
Publisher: Oxford University Press (OUP)
Date: 06-09-2017
Publisher: EDP Sciences
Date: 11-2020
DOI: 10.1051/0004-6361/202038894
Abstract: Aims. We present the results of three commissioning H I observations obtained with the MeerKAT radio telescope. These observations make up part of the preparation for the forthcoming MHONGOOSE nearby galaxy survey, which is a MeerKAT large survey project that will study the accretion of gas in galaxies and the link between gas and star formation. Methods. We used the available H I data sets, along with ancillary data at other wavelengths, to study the morphology of the MHONGOOSE s le galaxy, ESO 302-G014, which is a nearby gas-rich dwarf galaxy. Results. We find that ESO 302-G014 has a lopsided, asymmetric outer disc with a low column density. In addition, we find a tail or filament of H I clouds extending away from the galaxy, as well as an isolated H I cloud some 20 kpc to the south of the galaxy. We suggest that these features indicate a minor interaction with a low-mass galaxy. Optical imaging shows a possible dwarf galaxy near the tail, but based on the current data, we cannot confirm any association with ESO 302-G014. Nonetheless, an interaction scenario with some kind of low-mass companion is still supported by the presence of a significant amount of molecular gas, which is almost equal to the stellar mass, and a number of prominent stellar clusters, which suggest recently triggered star formation. Conclusions. These data show that MeerKAT produces exquisite imaging data. The forthcoming full-depth survey observations of ESO 302-G014 and other s le galaxies will, therefore, offer insights into the fate of neutral gas as it moves from the intergalactic medium onto galaxies.
Publisher: Oxford University Press (OUP)
Date: 06-08-2021
Abstract: We present a comprehensive multifrequency catalogue of radio sources behind the Large Magellanic Cloud (LMC) between 0.2 and 20 GHz, gathered from a combination of new and legacy radio continuum surveys. This catalogue covers an area of ∼144 deg2 at angular resolutions from 45 arcsec to ∼3 arcmin. We find 6434 discrete radio sources in total, of which 3789 are detected at two or more radio frequencies. We estimate the median spectral index (α where Sv ∼ να) of α = −0.89 and mean of −0.88 ± 0.48 for 3636 sources detected exclusively at two frequencies (0.843 and 1.384 GHz) with similar resolution [full width at half-maximum (FWHM) ∼40–45 arcsec]. The large frequency range of the surveys makes it an effective tool to investigate Gigahertz Peak Spectrum (GPS), Compact Steep Spectrum (CSS), and Infrared Faint Radio Source (IFRS) populations within our s le. We find 10 GPS candidates with peak frequencies near 5 GHz, from which we estimate their linear size. 1866 sources from our catalogue are CSS candidates with α & −0.8. We found six candidates for High Frequency Peaker (HFP) sources, whose radio fluxes peak above 5 GHz and no sources with unconstrained peaks and α & 0.5. We found optical counterparts for 343 of the radio continuum sources, of which 128 have a redshift measurement. Finally, we investigate the population of 123 IFRSs found in this study.
Publisher: Oxford University Press (OUP)
Date: 2005
Publisher: American Astronomical Society
Date: 13-04-2010
Publisher: Cambridge University Press (CUP)
Date: 08-2018
DOI: 10.1017/S1743921318006798
Abstract: Here I briefly highlight our studies of the gas content, kinematics and star formation in nearby dwarf galaxies ( D 10 Mpc) based on the ‘Local Volume H i Survey’ (LVHIS, Koribalski et al . 2018), which was conducted with the Australia Telescope Compact Array (ATCA). The LVHIS s le consists of nearly 100 galaxies, including new discoveries, spanning a large ersity in size, shape, mass and degree of peculiarity. The hydrogen properties of dwarf galaxies in two nearby groups, Sculptor and CenA / M83, are analysed and compared with many rather isolated dwarf galaxies. Around 10% of LVHIS galaxies are transitional or mixed-type dwarf galaxies (dIrr/dSph), the formation of which is explored. — I also provide a brief update on WALLABY Early Science , where we focus on studying the H i properties of galaxies as a function of environment. WALLABY (Dec +30 degr, z 0.26) is conducted with the Australian SKA Pathfinder (ASKAP), a ∽6-km diameter array of 36 × 12-m dishes, each equipped with wide-field (30 sq degr) Chequerboard Phased Array Feeds.
Publisher: American Astronomical Society
Date: 07-02-2018
Publisher: Cambridge University Press (CUP)
Date: 12-2021
DOI: 10.1017/S1743921321000879
Abstract: Open Astronomy is an important and valuable goal, including the availability of refereed science papers and user-friendly public astronomy data archives. The latter allow and encourage interested researchers from around the world to visualise, analyse and possibly download data from many different science and frequency domains. With the enormous growth of data volumes and complexity, open archives are essential to explore ideas and make discoveries. Open source software is equally important for many reasons, including reproducibility and collaboration. I will present ex les of open archive and software tools, including the CSIRO ASKAP Science Data Archive (CASDA), the Local Volume HI Survey (LVHIS), the 3D Source Finding Application (SoFiA) and the Busy Function (BF). Astronomy is international and includes or links to an incredibly wide range of sciences, computing, engineering, and education. Its open nature can serve as an ex le for world-wide interdisciplinary collaborations.
Publisher: American Astronomical Society
Date: 24-05-2011
Publisher: Oxford University Press (OUP)
Date: 12-05-2021
Abstract: In the broad context of the Australian Square Kilometer Array Pathfinder (ASKAP) early-science phase and preparation for the related surveys, we report the first radio observations towards the Galactic plane. The targeted field was chosen to encompass the entire SCORPIO survey, one of the several pathfinder projects for the Evolutionary Map of the Universe survey planned with the ASKAP. The observations were carried out in 2018 January at a central frequency of 912 MHz, with 15 operational antennas, and covered a total area of about 40 square degrees in three different pointings. The final image has a resolution of 24.1 × 21.1 arcsec2 and a median rms of $541\\ \\mu \\mathrm{Jy\\ beam}^{-1}$. We were able to extract 3545 candidate sources, 75 per cent of them point sources. For a preliminary validation, a comparison with the 843 MHz Molonglo Galactic Plane Survey is presented. Although the present observations were obtained with the ASKAP only partially deployed, its unique capability to map complex sources, such as those inhabiting the Galactic plane, at different angular scales, is highlighted. Within the SCORPIO field all the previously classified H ii regions, Planetary Nebulae (PNe), and supernovae remnants (SNRs), previously known to be radio sources, were detected. We also report new radio detections from several H ii regions previously classified as ‘candidates’ or ‘radio quiet’ and from half of all the PNe in the SCORPIO field with robust classification. Most notably, we find numerous unclassified, extended sources which constitute a promising s le of candidates H ii regions and SNRs.
Publisher: American Astronomical Society
Date: 17-06-2216
DOI: 10.1086/307314
Publisher: Oxford University Press (OUP)
Date: 21-07-2017
Publisher: EDP Sciences
Date: 27-03-2023
DOI: 10.1051/0004-6361/202245640
Abstract: Context. Multifrequency studies of galaxy clusters are crucial for inferring their dynamical states and physics. Moreover, these studies allow us to investigate cluster-embedded sources, whose evolution is affected by the physical and dynamical condition of the cluster itself. So far, these kinds of studies have been preferentially conducted on clusters visible from the northern hemisphere due to the high-fidelity imaging capabilities of ground-based radio interferometers located there. Aims. In this paper, we conducted a multifrequency study of the poorly known galaxy cluster Abell 3718. We investigated the unknown origin of an extended radio source with a length of ∼612 kpc at 943 MHz detected in images from the Evolutionary Map of the Universe (EMU) and POlarisation Sky Survey of the Universe’s Magnetism (POSSUM) surveys. Methods. We analyzed optical and X-ray data to infer the dynamical state of the cluster and, in particular, the merger activity. We conducted a radio spectral index study from 943 MHz up to 9 GHz. We also evaluated the polarization properties of the brightest cluster-embedded sources to understand if they are related to the radio emission observed on larger scales. Results. The cluster appears to be in a relaxed dynamical state, but there is clear asymmetry of the X-ray surface brightness distribution perpendicular to the direction of the largest angular extension of the radio source. The morphology of the cluster radio emission observed from 900 MHz to 9 GHz shows a system composed of a northern compact radio source and a southern radio galaxy whose jets are bent in the direction of an ultra-steep ( α ≈ 3.6), thin (few tens of kpc) arc of radio emission between the first two radio sources. The spectral index gradient along the radio source and the polarization images at high frequency suggest that the thin arc is an extension of the southern radio galaxy, which may have been energized by interacting with the X-ray gas. An additional structure extending to the northwest from the southern radio galaxy may be an unusual truncated radio jet that either failed to expand or faded away due to energy losses. Deeper X-ray and radio observations are needed to better constrain the physics at play in this cluster.
Publisher: Oxford University Press (OUP)
Date: 08-05-2006
Publisher: Cambridge University Press (CUP)
Date: 2017
DOI: 10.1017/PASA.2017.41
Abstract: The Taipan galaxy survey (hereafter simply ‘Taipan’) is a multi-object spectroscopic survey starting in 2017 that will cover 2π steradians over the southern sky (δ ≲ 10°, | b | ≳ 10°), and obtain optical spectra for about two million galaxies out to z 0.4. Taipan will use the newly refurbished 1.2-m UK Schmidt Telescope at Siding Spring Observatory with the new TAIPAN instrument, which includes an innovative ‘Starbugs’ positioning system capable of rapidly and simultaneously deploying up to 150 spectroscopic fibres (and up to 300 with a proposed upgrade) over the 6° diameter focal plane, and a purpose-built spectrograph operating in the range from 370 to 870 nm with resolving power R ≳ 2000. The main scientific goals of Taipan are (i) to measure the distance scale of the Universe (primarily governed by the local expansion rate, H 0 ) to 1% precision, and the growth rate of structure to 5% (ii) to make the most extensive map yet constructed of the total mass distribution and motions in the local Universe, using peculiar velocities based on improved Fundamental Plane distances, which will enable sensitive tests of gravitational physics and (iii) to deliver a legacy s le of low-redshift galaxies as a unique laboratory for studying galaxy evolution as a function of dark matter halo and stellar mass and environment. The final survey, which will be completed within 5 yrs, will consist of a complete magnitude-limited s le ( i ⩽ 17) of about 1.2 × 10 6 galaxies supplemented by an extension to higher redshifts and fainter magnitudes ( i ⩽ 18.1) of a luminous red galaxy s le of about 0.8 × 10 6 galaxies. Observations and data processing will be carried out remotely and in a fully automated way, using a purpose-built automated ‘virtual observer’ software and an automated data reduction pipeline. The Taipan survey is deliberately designed to maximise its legacy value by complementing and enhancing current and planned surveys of the southern sky at wavelengths from the optical to the radio it will become the primary redshift and optical spectroscopic reference catalogue for the local extragalactic Universe in the southern sky for the coming decade.
Publisher: Oxford University Press (OUP)
Date: 03-2004
Publisher: EDP Sciences
Date: 06-2014
Publisher: Oxford University Press (OUP)
Date: 31-03-2011
Publisher: Oxford University Press (OUP)
Date: 03-08-2013
Publisher: Oxford University Press (OUP)
Date: 03-01-2015
Publisher: Oxford University Press (OUP)
Date: 11-08-2021
Abstract: We use high-resolution ASKAP observations of galaxies in the Eridanus supergroup to study their H i, angular momentum, and star formation properties, as part of the WALLABY pre-pilot survey efforts. The Eridanus supergroup is composed of three sub-groups in the process of merging to form a cluster. The main focus of this study is the Eridanus (or NGC 1395) sub-group. The baryonic specific angular momentum – baryonic mass (jb−Mb) relation for the Eridanus galaxies is observed to be an unbroken power law of the form $j_{\\mathrm{b}} \\propto M_{\\mathrm{b}}^{0.57 \\pm 0.05}$, with a scatter of ∼0.10 ± 0.01 dex, consistent with previous works. We examine the relation between the atomic gas fraction, fatm, and the integrated atomic disc stability parameter q (the fatm−q relation), and find that the Eridanus galaxies deviate significantly from the relation owing to environmental processes such as tidal interactions and ram pressure affecting their H i gas. We find that a majority of the Eridanus galaxies are H i deficient compared to normal star-forming galaxies in the field. We also find that the star formation among the Eridanus galaxies may be suppressed owing to their environment, thus hinting at significant levels of pre-processing within the Eridanus sub-group, even before the galaxies have entered a cluster-like environment.
Publisher: American Astronomical Society
Date: 07-2001
DOI: 10.1086/321453
Publisher: Cambridge University Press (CUP)
Date: 07-2014
DOI: 10.1017/S1743921314009326
Abstract: We are conducting a multiwavelength study of XUV discs in nearby, gas-rich spiral galaxies combining the available UV (GALEX) observations with H i data obtained at the ATCA as part of the Local Volume HI Survey (LVHIS) project and multi-object fibre spectroscopy obtained using the 2dF/AAOmega instrument at the 3.9m AAT. Here we present the results of the multiwavelength analysis of the galaxy pair NGC 1512/1510. The H i distribution of NGC 1512 is very extended with two pronounced spiral/tidal arms. Hundreds of independent UV-bright regions are associated with dense H i clouds in the galaxy outskirts. We confirm the detection of ionized gas in the majority of them and characterize their physical properties, chemical abundances and kinematics. Both the gas distribution andthe distribution of the star-forming regions are affected by gravitational interactionwith the neighbouring blue compact dwarf galaxy NGC 1510. Our multiwavelength analysis provides new clues about local star-formation processes, the metal redistribution in the outer gaseous discs of spiral galaxies, the importance of galaxy interactions, the fate of the neutral gas and the chemical evolution in nearby galaxies.
Publisher: Oxford University Press (OUP)
Date: 28-12-2015
Publisher: American Astronomical Society
Date: 20-06-2013
Publisher: EDP Sciences
Date: 26-02-2021
DOI: 10.1051/0004-6361/202039590
Abstract: Context. Inferences about dark matter, dark energy, and the missing baryons all depend on the accuracy of our model of large-scale structure evolution. In particular, with cosmological simulations in our model of the Universe, we trace the growth of structure, and visualize the build-up of bigger structures from smaller ones and of gaseous filaments connecting galaxy clusters. Aims. Here we aim to reveal the complexity of the large-scale structure assembly process in great detail and on scales from tens of kiloparsecs up to more than 10 Mpc with new sensitive large-scale observations from the latest generation of instruments. We also aim to compare our findings with expectations from our cosmological model. Methods. We used dedicated SRG/eROSITA performance verification (PV) X-ray, ASKAP/EMU Early Science radio, and DECam optical observations of a ~15 deg 2 region around the nearby interacting galaxy cluster system A3391/95 to study the warm-hot gas in cluster outskirts and filaments, the surrounding large-scale structure and its formation process, the morphological complexity in the inner parts of the clusters, and the (re-)acceleration of plasma. We also used complementary Sunyaev-Zeldovich (SZ) effect data from the Planck survey and custom-made Galactic total (neutral plus molecular) hydrogen column density maps based on the HI4PI and IRAS surveys. We relate the observations to expectations from cosmological hydrodynamic simulations from the Magneticum suite. Results. We trace the irregular morphology of warm and hot gas of the main clusters from their centers out to well beyond their characteristic radii, r 200 . Between the two main cluster systems, we observe an emission bridge on large scale and with good spatial resolution. This bridge includes a known galaxy group but this can only partially explain the emission. Most gas in the bridge appears hot, but thanks to eROSITA’s unique soft response and large field of view, we discover some tantalizing hints for warm, truly primordial filamentary gas connecting the clusters. Several matter clumps physically surrounding the system are detected. For the “Northern Clump,” we provide evidence that it is falling towards A3391 from the X-ray hot gas morphology and radio lobe structure of its central AGN. Moreover, the shapes of these X-ray and radio structures appear to be formed by gas well beyond the virial radius, r 100 , of A3391, thereby providing an indirect way of probing the gas in this elusive environment. Many of the extended sources in the field detected by eROSITA are also known clusters or new clusters in the background, including a known SZ cluster at redshift z = 1. We find roughly an order of magnitude more cluster candidates than the SPT and ACT surveys together in the same area. We discover an emission filament north of the virial radius of A3391 connecting to the Northern Clump. Furthermore, the absorption-corrected eROSITA surface brightness map shows that this emission filament extends south of A3395 and beyond an extended X-ray-emitting object (the “Little Southern Clump”) towards another galaxy cluster, all at the same redshift. The total projected length of this continuous warm-hot emission filament is 15 Mpc, running almost 4 degrees across the entire eROSITA PV observation field. The Northern and Southern Filament are each detected at σ . The Planck SZ map additionally appears to support the presence of both new filaments. Furthermore, the DECam galaxy density map shows galaxy overdensities in the same regions. Overall, the new datasets provide impressive confirmation of the theoretically expected structure formation processes on the in idual system level, including the surrounding warm-hot intergalactic medium distribution the similarities of features found in a similar system in the Magneticum simulation are striking. Our spatially resolved findings show that baryons indeed reside in large-scale warm-hot gas filaments with a clumpy structure.
Publisher: EDP Sciences
Date: 06-2001
Publisher: Oxford University Press (OUP)
Date: 21-04-2015
DOI: 10.1093/MNRAS/STV504
Publisher: Oxford University Press (OUP)
Date: 04-12-2021
Abstract: We present results from our analysis of the Hydra I cluster observed in neutral atomic hydrogen (H i) as part of the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY). These WALLABY observations cover a 60-square-degree field of view with uniform sensitivity and a spatial resolution of 30 arcsec. We use these wide-field observations to investigate the effect of galaxy environment on H i gas removal and star formation quenching by comparing the properties of cluster, infall, and field galaxies extending up to ∼5R200 from the cluster centre. We find a sharp decrease in the H i-detected fraction of infalling galaxies at a projected distance of ∼1.5R200 from the cluster centre from $\\sim 85{{\\ \\rm per\\ cent}}$ to $\\sim 35{{\\ \\rm per\\ cent}}$. We see evidence for the environment removing gas from the outskirts of H i-detected cluster and infall galaxies through the decrease in the H i to r-band optical disc diameter ratio. These galaxies lie on the star-forming main sequence, indicating that gas removal is not yet affecting the inner star-forming discs and is limited to the galaxy outskirts. Although we do not detect galaxies undergoing galaxy-wide quenching, we do observe a reduction in recent star formation in the outer disc of cluster galaxies, which is likely due to the smaller gas reservoirs present beyond the optical radius in these galaxies. Stacking of H i non-detections with H i masses below $M_{\\rm {HI}}\\lesssim 10^{8.4}\\, \\rm {M}_{\\odot }$ will be required to probe the H i of galaxies undergoing quenching at distances ≳60 Mpc with WALLABY.
Publisher: American Astronomical Society
Date: 10-04-2000
DOI: 10.1086/308634
Publisher: EDP Sciences
Date: 07-2010
Publisher: Oxford University Press (OUP)
Date: 09-01-2017
DOI: 10.1093/MNRAS/STX012
Publisher: Oxford University Press (OUP)
Date: 06-1998
Publisher: Springer Science and Business Media LLC
Date: 07-2020
Publisher: Oxford University Press (OUP)
Date: 27-05-2019
Abstract: This paper reports on the atomic hydrogen gas (H i) observations of the spiral galaxy NGC 1566 using the newly commissioned Australian Square Kilometre Array Pathfinder radio telescope. We measure an integrated H i flux density of $180.2$ Jy km s−1 emanating from this galaxy, which translates to an H i mass of $1.94\\times 10^{10}\\, \\mathrm{ M}_{\\odot }$ at an assumed distance of $21.3$ Mpc. Our observations show that NGC 1566 has an asymmetric and mildly warped H i disc. The H i-to-stellar mass fraction (M$_{\\rm{H\\,{{\\small I}}}}$/M∗) of NGC 1566 is 0.29, which is high in comparison with galaxies that have the same stellar mass ($10^{10.8}$ M⊙). We also derive the rotation curve of this galaxy to a radius of $50$ kpc and fit different mass models to it. The NFW, Burkert, and pseudo-isothermal dark matter halo profiles fit the observed rotation curve reasonably well and recover dark matter fractions of 0.62, 0.58, and 0.66, respectively. Down to the column density sensitivity of our observations ($N_{\\rm{H\\,{{\\small I}}}}\\, =\\, 3.7\\times 10^{19}$ cm−2), we detect no H i clouds connected to, or in the nearby vicinity of, the H i disc of NGC 1566 nor nearby interacting systems. We conclude that, based on a simple analytic model, ram pressure interactions with the IGM can affect the H i disc of NGC 1566 and is possibly the reason for the asymmetries seen in the H i morphology of NGC 1566.
Publisher: American Astronomical Society
Date: 07-1999
DOI: 10.1086/300907
Publisher: Oxford University Press (OUP)
Date: 06-02-2021
Abstract: We combine observations from Atacama Large Millimeter/submillimeter Array (ALMA), Australia Telescope Compact Array, Multi Unit Spectroscopic Explorer (MUSE), and Herschel to study gas-to-dust ratios in 15 Fornax cluster galaxies detected in the FIR/sub-mm by Herschel and observed by ALMA as part of the ALMA Fornax Cluster Survey. The s le spans a stellar mass range of 8.3 ≤ log(M⋆/M⊙) ≤ 11.16, and a variety of morphological types. We use gas-phase metallicities derived from MUSE observations (from the Fornax3D survey) to study these ratios as a function of metallicity, and to study dust-to-metal ratios, in a sub-s le of nine galaxies. We find that gas-to-dust ratios in Fornax galaxies are systematically lower than those in field galaxies at fixed stellar mass/metallicity. This implies that a relatively large fraction of the metals in these Fornax systems is locked up in dust, which is possibly due to altered chemical evolution as a result of the dense environment. The low ratios are not only driven by H i deficiencies, but H2-to-dust ratios are also significantly decreased. This is different in the Virgo cluster, where low gas-to-dust ratios inside the virial radius are driven by low H i-to-dust ratios, while H2-to-dust ratios are increased. Resolved observations of NGC 1436 show a radial increase in H2-to-dust ratio, and show that low ratios are present throughout the disc. We propose various explanations for the low H2-to-dust ratios in the Fornax cluster, including the more efficient stripping of H2 compared to dust, more efficient enrichment of dust in the star formation process, and altered interstellar medium physics in the cluster environment.
Publisher: Oxford University Press (OUP)
Date: 21-09-2019
Abstract: We present two new radio continuum images from the Australian Square Kilometre Array Pathfinder (ASKAP) survey in the direction of the Small Magellanic Cloud (SMC). These images are part of the Evolutionary Map of the Universe (EMU) Early Science Project (ESP) survey of the Small and Large Magellanic Clouds. The two new source lists produced from these images contain radio continuum sources observed at 960 MHz (4489 sources) and 1320 MHz (5954 sources) with a bandwidth of 192 MHz and beam sizes of 30.0 × 30.0 arcsec2 and 16.3 × 15.1 arcsec2, respectively. The median root mean square (RMS) noise values are 186 $\\mu$Jy beam−1 (960 MHz) and 165 $\\mu$Jy beam−1 (1320 MHz). To create point source catalogues, we use these two source lists, together with the previously published Molonglo Observatory Synthesis Telescope (MOST) and the Australia Telescope Compact Array (ATCA) point source catalogues to estimate spectral indices for the whole population of radio point sources found in the survey region. Combining our ASKAP catalogues with these radio continuum surveys, we found 7736 point-like sources in common over an area of 30 deg2. In addition, we report the detection of two new, low surface brightness supernova remnant candidates in the SMC. The high sensitivity of the new ASKAP ESP survey also enabled us to detect the bright end of the SMC planetary nebula s le, with 22 out of 102 optically known planetary nebulae showing point-like radio continuum emission. Lastly, we present several morphologically interesting background radio galaxies.
Publisher: Oxford University Press (OUP)
Date: 12-06-2018
Publisher: American Astronomical Society
Date: 30-11-2012
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.46
Publisher: Oxford University Press (OUP)
Date: 23-02-2015
DOI: 10.1093/MNRAS/STV079
Publisher: Oxford University Press (OUP)
Date: 15-01-2018
DOI: 10.1093/MNRAS/STY105
Publisher: Oxford University Press (OUP)
Date: 02-2004
Publisher: Oxford University Press (OUP)
Date: 08-12-2022
Abstract: The optical morphology of galaxies is strongly related to galactic environment, with the fraction of early-type galaxies increasing with local galaxy density. In this work, we present the first analysis of the galaxy morphology–density relation in a cosmological hydrodynamical simulation. We use a convolutional neural network, trained on observed galaxies, to perform visual morphological classification of galaxies with stellar masses $M_\\ast \\gt 10^{10} \\, \\rm {M}_{\\odot }$ in the EAGLE simulation into elliptical, lenticular and late-type (spiral/irregular) classes. We find that EAGLE reproduces both the galaxy morphology–density and morphology–mass relations. Using the simulations, we find three key processes that result in the observed morphology–density relation: (i) transformation of disc-dominated galaxies from late-type (spiral) to lenticular galaxies through gas stripping in high-density environments, (ii) formation of lenticular galaxies by merger-induced black hole feedback in low-density environments, and (iii) an increasing fraction of high-mass galaxies, which are more often elliptical galaxies, at higher galactic densities.
Publisher: Cambridge University Press (CUP)
Date: 03-2016
DOI: 10.1017/S1743921316011601
Abstract: The outskirts of galaxies — especially the very extended H i disks of galaxies — are strongly affected by their local environment. I highlight the giant 2X-H i disks of nearby galaxies (M 83, NGC 3621, and NGC 1512), studied as part of the Local Volume H i Survey (LVHIS), their kinematics and relation to XUV disks, signatures of tidal interactions and accretion events, the M HI - D HI relation as well as the formation of tidal dwarf galaxies. - Using multi-wavelength data, I create 3D visualisations of the gas and stars in galaxies, with the shape of their warped disks obtained through kinematic modelling of their H i velocity fields.
Publisher: Oxford University Press (OUP)
Date: 12-09-2022
Abstract: We present the discovery of highly collimated radio jets spanning a total of 355 kpc around the nearby elliptical galaxy NGC 2663, and the possible first detection of recollimation on kiloparsec scales. The small distance to the galaxy (∼28.5 Mpc) allows us to resolve portions of the jets to examine their structure. We combine multiwavelength data: radio observations by the Murchison Widefield Array (MWA), the Australian Square Kilometre Array Pathfinder (ASKAP) and the Australia Telescope Compact Array (ATCA), and X-ray data from Chandra, Swift, and SRG/eROSITA. We present intensity, rotation measure, polarization, spectral index, and X-ray environment maps. Regions of the southern jet show simultaneous narrowing and brightening, which can be interpreted as a signature of the recollimation of the jet by external, environmental pressure, though it is also consistent with intermittent active galactic nuclei or complex internal jet structure. X-ray data suggest that the environment is extremely poor if the jet is indeed recollimating, the large recollimation scale (40 kpc) is consistent with a slow jet in a low-density environment.
Publisher: EDP Sciences
Date: 05-2022
DOI: 10.1051/0004-6361/202141415
Abstract: Context. Galaxy clusters grow through mergers and the accretion of substructures along large-scale filaments. Many of the missing baryons in the local Universe may reside in such filaments as the warm-hot intergalactic medium (WHIM). Aims. SRG/eROSITA performance verification observations revealed that the binary cluster Abell 3391/3395 and the Northern Clump (the MCXC J0621.7–5242 galaxy cluster) are aligning along a cosmic filament in soft X-rays, similarly to what has been seen in simulations before. We aim to understand the dynamical state of the Northern Clump as it enters the atmosphere (3 × R 200 ) of Abell 3391. Methods. We analyzed joint eROSITA, XMM-Newton , and Chandra observations to probe the morphological, thermal, and chemical properties of the Northern Clump from its center out to a radius of 988 kpc ( R 200 ). We utilized the ASKAP/EMU radio data, the DECam optical image, and the Planck y -map to study the influence of the wide-angle tail (WAT) radio source on the Northern Clump’s central intracluster medium. Using eROSITA data, we also analyzed the gas properties of the Northern Filament, the region between the virial radii of the Northern Clump and the A3391 cluster. From the Magneticum simulation, we identified an analog of the A3391/95 system along with an infalling group resembling the Northern Clump. Results. The Northern Clump is a weak cool-core cluster centered on a WAT radio galaxy. The gas temperature over 0.2–0.5 R 500 is k B T 500 = 1.99 ± 0.04 keV. We employed the mass-temperature (M – T ) scaling relation and obtained a mass estimate of M 500 = (7.68 ± 0.43) × 10 13 M ⊙ and R 500 = (63 6 ± 12) kpc. Its X-ray atmosphere has a boxy shape and deviates from spherical symmetry. We identify a southern surface brightness edge, likely caused by subsonic motion relative to the filament gas in the southern direction. At ~ R 500 , the southern atmosphere (infalling head) appears to be 42% hotter than its northern atmosphere. We detect a downstream tail pointing toward the north with a projected length of ~318 kpc, plausibly the result of ram pressure stripping. Through a two-temperature fit, we identify a cooler component in the Northern Filament with k B T = 0.68 - 0.64 + 0.38 keV and n e = 1.99 -1.24 +0.88 × 10 -5 cm -3 , which are consistent within the expected ranges of WHIM properties. The analog group in the Magneticum simulation is experiencing changes in its gas properties and a shift between the position of the halo center and that of the bound gas, while approaching the main cluster pair. Conclusions. The Northern Clump is a dynamically active system and far from being relaxed. Its atmosphere is affected by an interaction with the WAT and by gas sloshing or its infall toward Abell 3391 along the filament, consistent with the analog group-size halo in the Magneticum simulation.
Publisher: Oxford University Press (OUP)
Date: 12-09-2022
Publisher: Oxford University Press (OUP)
Date: 25-09-2014
Publisher: Oxford University Press (OUP)
Date: 26-09-2017
Publisher: Elsevier BV
Date: 11-1999
Publisher: Oxford University Press (OUP)
Date: 10-2006
Publisher: Oxford University Press (OUP)
Date: 18-08-2022
Abstract: We present the results of a search for associated 21 cm H i absorption at redshift 0.42 & z & 1.00 in radio-loud galaxies from three Galaxy And Mass Assembly (GAMA) survey fields. These observations were carried out as part of a pilot survey for the Australian SKA Pathfinder (ASKAP) First Large Absorption Survey in H i (FLASH). From a s le of 326 radio sources with 855.5 MHz peak flux density above 10 mJy, we detected two associated H i absorption systems, in SDSS J090331+010847 at z = 0.522 and SDSS J113622+004852 at z = 0.563. Both galaxies are massive (stellar mass $\\gt 10^{11}\\, \\mathrm{M}_\\odot$) and have optical spectra characteristic of luminous red galaxies, though spectral energy distribution fitting implies that SDSS J113622+004852 contains a dust-obscured starburst with star formation rate ∼69 M⊙ yr−1. The H i absorption lines have a high optical depth, with τpk of 1.77 ± 0.16 for SDSS J090331+010847 (the highest value for any z & 0.1 associated system found to date) and 0.14 ± 0.01 for SDSS J113622+004852. In the redshift range probed by our ASKAP observations, the detection rate for associated H i absorption lines (with τpk & 0.1 and at least 3σ significance) is $2.9_{-2.6}^{+9.7}$ per cent. Although the current s le is small, this rate is consistent with a trend seen in other studies for a lower detection rate of associated 21 cm H i absorption systems at higher redshift. We also searched for OH absorption lines at 0.67 & z & 1.34, but no detection was made in the 145 radio sources searched.
Publisher: American Astronomical Society
Date: 06-2007
DOI: 10.1086/517867
Publisher: American Astronomical Society
Date: 02-2023
Abstract: Observations with the Hubble Space Telescope unexpectedly revealed that the dwarf galaxy ESO 006–001 is a near neighbor to the Local Group at a distance of 2.70 ± 0.11 Mpc. The stellar population in the galaxy is well resolved into in idual stars to a limit of M I ∼ − 0.5 mag. The dominant population is older than 12 Gyr yet displays a significant range in metallicity of −2 [Fe/H] − 1, as evidenced by a red giant branch with substantial width. Superimposed on the dominant population are stars on the main sequence with ages less than 100 Myr and helium burning blue loop stars with ages of several hundred Myr. ESO 006–001 is an ex le of a transition dwarf a galaxy dominated by old stars but one that has experienced limited recent star formation in a swath near the center. No H i gas is detected at the location of the optical galaxy in spite of the evidence for young stars. Intriguingly, an H i cloud with a similar redshift is detected 9 kpc away in projection. Otherwise, ESO 006–001 is a galaxy in isolation with its nearest known neighbor IC 3104, itself a dwarf, at a distance of ∼500 kpc.
Publisher: American Astronomical Society
Date: 09-2000
DOI: 10.1086/301542
Publisher: Oxford University Press (OUP)
Date: 11-03-1996
Publisher: American Astronomical Society
Date: 07-2006
DOI: 10.1086/504685
Publisher: American Astronomical Society
Date: 04-2000
DOI: 10.1086/301303
Publisher: Elsevier BV
Date: 09-2005
Publisher: American Astronomical Society
Date: 20-09-2006
DOI: 10.1086/504681
Publisher: Oxford University Press (OUP)
Date: 19-10-2022
Publisher: Oxford University Press (OUP)
Date: 19-12-2023
Abstract: ESO 137-G006 is the brightest cluster galaxy (BCG) of the cool-core and dynamically young Norma cluster. We discover an atomic hydrogen (H i) absorption line associated with this BCG using the Australia Telescope Compact Array. We estimate a gas column density of $\\approx (1.3 \\pm 0.2) \\times 10^{20}\\, T_{\\rm {spin}}$ atoms cm−2 with spin temperature, Tspin ≤ 194 K, consistent with the H i properties of other early-type galaxies and cool-core cluster BCGs. The relationship between the presence of cold gas and a cluster cooling flow is unclear. Our results support the scenario that ESO 137-G006 may be a recent arrival to the cluster centre and not the original BCG. This scenario is consistent with the observed spatial alignment of the BCG’s wide-angle tail radio lobes with Norma’s X-ray sub-cluster and the significant line-of-sight velocity offset between the mean velocity of Norma and that of the BCG.
Publisher: Oxford University Press (OUP)
Date: 04-02-2022
Abstract: We report the discovery of J0624–6948, a low-surface brightness radio ring, lying between the Galactic Plane and the large magellanic cloud (LMC). It was first detected at 888 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP), and with a diameter of ∼196 arcsec. This source has phenomenological similarities to odd radio circles (ORCs). Significant differences to the known ORCs – a flatter radio spectral index, the lack of a prominent central galaxy as a possible host, and larger apparent size – suggest that J0624–6948 may be a different type of object. We argue that the most plausible explanation for J0624–6948 is an intergalactic supernova remnant due to a star that resided in the LMC outskirts that had undergone a single-degenerate type Ia supernova, and we are seeing its remnant expand into a rarefied, intergalactic environment. We also examine if a massive star or a white dwarf binary ejected from either galaxy could be the supernova progenitor. Finally, we consider several other hypotheses for the nature of the object, including the jets of an active galactic nucleus (30Dor) or the remnant of a nearby stellar super-flare.
Publisher: Oxford University Press (OUP)
Date: 13-10-2022
Abstract: We present a new Australian Square Kilometre Array Pathfinder (ASKAP) s le of 14 radio supernova remnants (SNR) candidates in the Large Magellanic Cloud (LMC). This new s le is a significant increase to the known number of older, larger, and low surface brightness LMC SNRs. We employ a multifrequency search for each object and found possible traces of optical and occasionally X-ray emission in several of these 14 SNR candidates. One of these 14 SNR candidates (MCSNR J0522 – 6543) has multifrequency properties that strongly indicate a bona fide SNR. We also investigate a s le of 20 previously suggested LMC SNR candidates and confirm the SNR nature of MCSNR J0506 – 6815. We detect lower surface brightness SNR candidates which were likely formed by a combination of shock waves and strong stellar winds from massive progenitors (and possibly surrounding OB stars). Some of our new SNR candidates are also found in lower density environments in which SNe type Ia explode inside a previously excavated interstellar medium.
Publisher: Oxford University Press (OUP)
Date: 13-09-2014
Publisher: Oxford University Press (OUP)
Date: 10-09-2022
Publisher: EDP Sciences
Date: 04-2022
Publisher: Oxford University Press (OUP)
Date: 20-02-2023
Abstract: The Evolutionary Map of the Universe (EMU) large-area radio continuum survey will detect tens of millions of radio galaxies, giving an opportunity for the detection of previously unknown classes of objects. To maximize the scientific value and make new discoveries, the analysis of these data will need to go beyond simple visual inspection. We propose the coarse-grained complexity, a simple scalar quantity relating to the minimum description length of an image that can be used to identify unusual structures. The complexity can be computed without reference to the broader s le or existing catalogue data, making the computation efficient on new surveys at very large scales (such as the full EMU survey). We apply our coarse-grained complexity measure to data from the EMU Pilot Survey to detect and confirm anomalous objects in this data set and produce an anomaly catalogue. Rather than work with existing catalogue data using a specific source detection algorithm, we perform a blind scan of the area, computing the complexity using a sliding square aperture. The effectiveness of the complexity measure for identifying anomalous objects is evaluated using crowd-sourced labels generated via the Zooniverse.org platform. We find that the complexity scan identifies unusual sources, such as odd radio circles, by partitioning on complexity. We achieve partitions where 5 per cent of the data is estimated to be 86 per cent complete, and 0.5 per cent is estimated to be 94 per cent pure, with respect to anomalies and use this to produce an anomaly catalogue.
Publisher: Oxford University Press (OUP)
Date: 21-05-2003
Publisher: Oxford University Press (OUP)
Date: 14-01-2016
Publisher: Springer Netherlands
Date: 2008
Publisher: EDP Sciences
Date: 26-02-2004
Publisher: American Astronomical Society
Date: 02-02-2007
DOI: 10.1086/510668
Publisher: Oxford University Press (OUP)
Date: 15-07-2019
Abstract: With the Australian Square Kilometre Array Pathfinder (ASKAP) we monitored the black hole candidate X-ray binary MAXI J1535–571 over seven epochs from 2017 September 21 to October 2. Using ASKAP observations, we studied the H i absorption spectrum from gas clouds along the line of sight and thereby constrained the distance to the source. The maximum negative radial velocities measured from the H i absorption spectra for MAXI J1535–571 and an extragalactic source in the same field of view are −69 ± 4 and −89 ± 4 km s−1, respectively. This rules out the far kinematic distance ($9.3^{+0.5}_{-0.6}$ kpc), giving a most likely distance of $4.1^{+0.6}_{-0.5}$ kpc, with a strong upper limit of the tangent point at $6.7^{+0.1}_{-0.2}$ kpc. At our preferred distance, the peak unabsorbed luminosity of MAXI J1535–571 was per cent of the Eddington luminosity, and shows that the soft-to-hard spectral state transition occurred at the very low luminosity of (1.2–3.4) × 10−5 times the Eddington luminosity. Finally, this study highlights the capabilities of new wide-field radio telescopes to probe Galactic transient outbursts, by allowing us to observe both a target source and a background comparison source in a single telescope pointing.
Publisher: Oxford University Press (OUP)
Date: 21-12-2009
Publisher: Oxford University Press (OUP)
Date: 18-12-2014
Publisher: EDP Sciences
Date: 07-2010
Publisher: Oxford University Press (OUP)
Date: 07-07-2006
Publisher: Oxford University Press (OUP)
Date: 04-01-2008
Publisher: Oxford University Press (OUP)
Date: 09-04-2020
Abstract: We present early science results from the First Large Absorption Survey in H i (FLASH), a spectroscopically blind survey for 21-cm absorption lines in cold hydrogen (H i) gas at cosmological distances using the Australian Square Kilometre Array Pathfinder (ASKAP). We have searched for H i absorption towards 1253 radio sources in the GAMA 23 field, covering redshifts between z = 0.34 and 0.79 over a sky area of approximately 50 deg2. In a purely blind search, we did not obtain any detections of 21-cm absorbers above our reliability threshold. Assuming a fiducial value for the H i spin temperature of Tspin = 100 K and source covering fraction cf = 1, the total comoving absorption path-length sensitive to all D ed Lyman α Absorbers (DLAs NH i ≥ 2 × 1020 cm−2) is ΔX = 6.6 ± 0.3 (Δz = 3.7 ± 0.2) and super-DLAs (NH i ≥ 2 × 1021 cm−2) is ΔX = 111 ± 6 (Δz= 63 ± 3). We estimate upper limits on the H i column density frequency distribution function that are consistent with measurements from prior surveys for redshifted optical DLAs, and nearby 21-cm emission and absorption. By cross-matching our s le of radio sources with optical spectroscopic identifications of galaxies in the GAMA 23 field, we were able to detect 21-cm absorption at z = 0.3562 towards NVSS J224500−343030, with a column density of $N_{\\rm H\\,\\small{I}} = (1.2 \\pm 0.1) \\times 10^{20}\\, (T_{\\rm spin}/100\\, \\mathrm{K})$ cm−2. The absorber is associated with GAMA J22450.05−343031.7, a massive early-type galaxy at an impact parameter of 17 kpc with respect to the radio source and which may contain a massive (MH i ≳ 3 × 109 M⊙) gas disc. Such gas-rich early types are rare, but have been detected in the nearby Universe.
Publisher: Oxford University Press (OUP)
Date: 31-10-2017
Publisher: American Association for the Advancement of Science (AAAS)
Date: 07-2005
Abstract: Stimulated emission of radiation has not been directly observed in astrophysical situations up to this time. Here we demonstrate that photons from pulsar B1641–45 stimulate pulses of excess 1720-megahertz line emission in an interstellar hydroxyl (OH) cloud. As this stimulated emission is driven by the pulsar, it varies on a few-millisecond time scale, which is orders of magnitude shorter than the quickest OH maser variations previously detected. Our 1612-megahertz spectra are inverted copies of the 1720-megahertz spectra. This “conjugate line” phenomenon enables us to constrain the properties of the interstellar OH line–producing gas. We also show that pulsar signals undergo significantly deeper OH absorption than do other background sources, which confirms earlier tentative findings that OH clouds are clumpier on small scales than are neutral hydrogen clouds.
Publisher: Oxford University Press (OUP)
Date: 31-07-2018
Publisher: Oxford University Press (OUP)
Date: 04-2013
DOI: 10.1093/MNRAS/STT555
Publisher: Oxford University Press (OUP)
Date: 06-2019
Abstract: We present an H i study of the galaxy group LGG 351 using Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) early science data observed with the Australian Square Kilometre Array Pathfinder (ASKAP). LGG 351 resides behind the M 83 group at a velocity range (cz) of ∼3500–4800 km s−1 within the rich Hydra-Centaurus overdensity region. We detect 40 sources with the discovery of a tidally interacting galaxy pair and two new H i sources that are not presented in previous optical catalogues. 23 out of 40 sources have new redshifts derived from the new H i data. This study is the largest WALLABY sub-s le to date and also allows us to further validate the performance of ASKAP and the data reduction pipeline askapsoft. Extended H i emission is seen in six galaxies indicating interaction within the group, although no H i debris is found. We also detect H i in a known ultra-faint dwarf galaxy (dw 1328−29), which demonstrates that it is not a satellite of the M 83 group as previously thought. In conjunction with multiwavelength data, we find that our galaxies follow the atomic gas fraction and baryonic Tully–Fisher scaling relations derived from the GALEX Arecibo SDSS Survey. In addition, majority of our galaxies fall within the star formation main sequence indicating inefficiency of gas removal processes in this loose galaxy group.
Publisher: Oxford University Press (OUP)
Date: 23-05-2019
Publisher: Cambridge University Press (CUP)
Date: 2016
DOI: 10.1017/PASA.2016.37
Abstract: We describe the performance of the Boolardy Engineering Test Array, the prototype for the Australian Square Kilometre Array Pathfinder telescope. Boolardy Engineering Test Array is the first aperture synthesis radio telescope to use phased array feed technology, giving it the ability to electronically form up to nine dual-polarisation beams. We report the methods developed for forming and measuring the beams, and the adaptations that have been made to the traditional calibration and imaging procedures in order to allow BETA to function as a multi-beam aperture synthesis telescope. We describe the commissioning of the instrument and present details of Boolardy Engineering Test Array’s performance: sensitivity, beam characteristics, polarimetric properties, and image quality. We summarise the astronomical science that it has produced and draw lessons from operating Boolardy Engineering Test Array that will be relevant to the commissioning and operation of the final Australian Square Kilometre Array Path telescope.
Publisher: American Astronomical Society
Date: 04-2009
Publisher: Oxford University Press (OUP)
Date: 25-10-2021
Abstract: We present results from a search for the H i 21-cm line in absorption towards 16 bright radio sources with the six-antenna commissioning array of the Australian Square Kilometre Array Pathfinder. Our targets were selected from the 2-Jy s le, a flux-limited survey of the southern radio sky with extensive multiwavelength follow-up. Two sources were detected in H i absorption including a new detection towards the bright Fanaroff–Riley Type II radio galaxy PKS 0409−75 at a redshift of $z$ = 0.674. The H i absorption line is blueshifted by ∼3300 km s−1 compared to the optical redshift of the host galaxy of PKS 0409−75 at $z$ = 0.693. Deep optical imaging and spectroscopic follow-up with the GMOS instrument on the Gemini-South telescope reveal that the H i absorption is associated with a galaxy in front of the southern radio lobe with a stellar mass of 3.2–6.8 × 1011 M⊙, a star formation rate of ∼1.24 M⊙ yr−1, and an estimated H i column density of 2.16 × 1021 cm−2, assuming a spin temperature of Tspin = 500 K and source covering factor of Cf = 0.3. Using polarization measurements of PKS 0409−75 from the literature, we estimate the magnetic field of the absorbing galaxy to be ∼14.5 $\\mu$G, consistent with field strengths observed in nearby spiral galaxies but larger than expected for an elliptical galaxy. Results from this pilot study can inform future surveys as new wide-field telescopes allow us to search for 21-cm H i absorption towards all bright radio sources as opposed to smaller targeted s les.
Publisher: Oxford University Press (OUP)
Date: 11-09-2006
Publisher: Oxford University Press (OUP)
Date: 26-07-2019
Abstract: We present a Wide-field ASKAP L-Band Legacy All-sky Blind surveY (WALLABY) study of the nearby (vsys = 915 km s−1) spiral galaxy IC 5201 using the Australian Square Kilometre Array Pathfinder (ASKAP). IC 5201 is a blue, barred spiral galaxy that follows the known scaling relations between stellar mass, SFR, H i mass, and diameter. We create a four-beam mosaicked H i image cube from 175 h of observations made with a 12-antenna sub-array. The root mean square noise level of the cube is 1.7 mJy beam−1 per channel, equivalent to a column density of $N_{\\rm H\\, \\small {I}}$ = 1.4 × 1020 cm−2 over 25 km s−1. We report nine extragalactic H i detections – five new H i detections including the first velocity measurements for two galaxies. These sources are IC 5201, three dwarf satellite galaxies, two galaxies, and a tidal feature belonging to the NGC 7232/3 triplet and two potential infalling galaxies to the triplet. There is evidence of a previous tidal interaction between IC 5201 and the irregular satellite AM 2220−460. A close fly-by is likely responsible for the asymmetric optical morphology of IC 5201 and warping its disc, resulting in the irregular morphology of AM 2220−460. We quantify the H i kinematics of IC 5201, presenting its rotation curve as well as showing that the warp starts at 14 kpc along the major axis, increasing as a function of radius with a maximum difference in position angle of 20°. There is no evidence of stripped H i, triggered or quenched star formation in the system as measured using DECam optical and GALEX UV photometry.
Publisher: Oxford University Press (OUP)
Date: 18-06-2018
Publisher: Cambridge University Press (CUP)
Date: 2016
DOI: 10.1017/PASA.2016.31
Abstract: We identify gravitationally bound structures in the Ursa Major region using positions, velocities and photometry from the Sloan Digital Sky Survey (SDSS DR7) and the Third Reference Catalogue of Bright Galaxies (RC3). A friends-of-friends algorithm is extensively tested on mock galaxy lightcones and then implemented on the real data to determine galaxy groups whose members are likely to be physically and dynamically associated with one another. We find several galaxy groups within the region that are likely bound to one another and in the process of merging. We classify 6 galaxy groups as the Ursa Major ‘supergroup’, which are likely to merge and form a poor cluster with a mass of ~ 8 × 10 13 M ⊙ . Furthermore, the Ursa Major supergroup as a whole is likely bound to the Virgo cluster, which will eventually form an even larger system in the context of hierarchical structure formation. We investigate the evolutionary state of the galaxy groups in the Ursa Major region and conclude that these groups are in an early evolutionary state and the properties of their member galaxies are similar to those in the field.
Publisher: EDP Sciences
Date: 11-2010
Publisher: American Astronomical Society
Date: 2005
DOI: 10.1086/426320
Publisher: Oxford University Press (OUP)
Date: 13-05-2015
DOI: 10.1093/MNRAS/STV703
Publisher: Oxford University Press (OUP)
Date: 29-10-2019
Publisher: American Astronomical Society
Date: 09-2022
Abstract: We present new results of a 12 CO( J = 1–0) imaging survey using the Atacama Compact Array (ACA) for 31 H i detected galaxies in the IC 1459 and NGC 4636 groups. This is the first CO imaging survey for loose galaxy groups. We obtained well-resolved CO data (∼0.7–1.5 kpc) for a total of 16 galaxies in two environments. By comparing our ACA CO data with the H i and UV data, we probe the impacts of the group environment on the cold gas components (CO and H i gas) and star formation activity. We find that CO and/or H i morphologies are disturbed in our group members, some of which show highly asymmetric CO distributions (e.g., IC 5264, NGC 7421, and NGC 7418). In comparison with isolated galaxies in the xCOLD GASS s le, our group galaxies tend to have low star formation rates and low H 2 gas fractions. Our findings suggest that the group environment can change the distribution of cold gas components, including the molecular gas and star formation properties of galaxies. This is supporting evidence that preprocessing in the group-like environment can play an important role in galaxy evolution.
Publisher: Oxford University Press (OUP)
Date: 27-09-2023
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.44
Abstract: We present a set of peculiar radio sources detected using an unsupervised machine learning method. We use data from the Australian Square Kilometre Array Pathfinder (ASKAP) telescope to train a self-organizing map (SOM). The radio maps from three ASKAP surveys, Evolutionary Map of Universe pilot survey (EMU-PS), Deep Investigation of Neutral Gas Origins pilot survey (DINGO), and Survey With ASKAP of GAMA-09 + X-ray (SWAG-X), are used to search for the rarest or unknown radio morphologies. We use an extension of the SOM algorithm that implements rotation and flipping invariance on astronomical sources. The SOM is trained using the images of all ‘complex’ radio sources in the EMU-PS which we define as all sources catalogued as ‘multi-component’. The trained SOM is then used to estimate a similarity score for complex sources in all surveys. We select 0.5% of the sources that are most complex according to the similarity metric and visually examine them to find the rarest radio morphologies. Among these, we find two new odd radio circle (ORC) candidates and five other peculiar morphologies. We discuss multiwavelength properties and the optical/infrared counterparts of selected peculiar sources. In addition, we present ex les of conventional radio morphologies including: diffuse emission from galaxy clusters, and resolved, bent-tailed, and FR-I and FR-II type radio galaxies. We discuss the overdense environment that may be the reason behind the circular shape of ORC candidates.
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.43
Abstract: We present the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY) Pilot Phase I H i kinematic models. This first data release consists of H i observations of three fields in the direction of the Hydra and Norma clusters, and the NGC 4636 galaxy group. In this paper, we describe how we generate and publicly release flat-disk tilted-ring kinematic models for 109/592 unique H i detections in these fields. The modelling method adopted here—which we call the WALLABY Kinematic Analysis Proto-Pipeline (WKAPP) and for which the corresponding scripts are also publicly available—consists of combining results from the homogeneous application of the FAT and 3DBarolo algorithms to the subset of 209 detections with sufficient resolution and $S/N$ in order to generate optimised model parameters and uncertainties. The 109 models presented here tend to be gas rich detections resolved by at least 3–4 synthesised beams across their major axes, but there is no obvious environmental bias in the modelling. The data release described here is the first step towards the derivation of similar products for thousands of spatially resolved WALLABY detections via a dedicated kinematic pipeline. Such a large publicly available and homogeneously analysed dataset will be a powerful legacy product that that will enable a wide range of scientific studies.
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.11
Abstract: We present the highest resolution and sensitivity $\\sim$ $1.4\\,$ GHz continuum observations of the Eridanus supergroup obtained as a part of the Widefield Australian Square Kilometer Array Pathfinder (ASKAP) L -band Legacy All-sky Blind surveY (WALLABY) pre-pilot observations using the ASKAP. We detect 9461 sources at 1.37 GHz down to a flux density limit of $\\sim$ $0.1$ mJy at $6.1''\\times 7.9''$ resolution with a median root mean square of 0.05 mJy beam $^{-1}$ . We find that the flux scale is accurate to within 5 % (compared to NVSS at 1.4 GHz). We then determine the global properties of eight Eridanus supergroup members, which are detected in both radio continuum and neutral hydrogen (HI) emission, and find that the radio-derived star formation rates (SFRs) agree well with previous literature. Using our global and resolved radio continuum properties of the nearby Eridanus galaxies, we measure and extend the infrared-radio correlation (IRRC) to lower stellar masses and inferred SFRs than before. We find the resolved IRRC to be useful for: (1) discriminating between active galactic nuclei and star-forming galaxies (2) identifying background radio sources and (3) tracing the effects of group environment pre-processing in NGC 1385. We find evidence for tidal interactions and ram-pressure stripping in the HI, resolved spectral index and IRRC morphologies of NGC 1385. There appears to be a spatial coincidence (in projection) of double-lobed radio jets with the central HI hole of NGC 1367. The destruction of polycyclic aromatic hydrocarbons by merger-induced shocks may be driving the observed WISE W3 deficit observed in NGC 1359. Our results suggest that resolved radio continuum and IRRC studies are excellent tracers of the physical processes that drive galaxy evolution and will be possible on larger s le of sources with upcoming ASKAP radio continuum surveys.
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2021.4
Abstract: We present the first Faraday rotation measure (RM) grid study of an in idual low-mass cluster—the Fornax cluster—which is presently undergoing a series of mergers. Exploiting commissioning data for the POlarisation Sky Survey of the Universe’s Magnetism (POSSUM) covering a ${\\sim}34$ square degree sky area using the Australian Square Kilometre Array Pathfinder (ASKAP), we achieve an RM grid density of ${\\sim}25$ RMs per square degree from a 280-MHz band centred at 887 MHz, which is similar to expectations for forthcoming GHz-frequency ${\\sim}3\\pi$ -steradian sky surveys. These data allow us to probe the extended magnetoionic structure of the cluster and its surroundings in unprecedented detail. We find that the scatter in the Faraday RM of confirmed background sources is increased by $16.8\\pm2.4$ rad m −2 within 1 $^\\circ$ (360 kpc) projected distance to the cluster centre, which is 2–4 times larger than the spatial extent of the presently detectable X-ray-emitting intracluster medium (ICM). The mass of the Faraday-active plasma is larger than that of the X-ray-emitting ICM and exists in a density regime that broadly matches expectations for moderately dense components of the Warm-Hot Intergalactic Medium. We argue that forthcoming RM grids from both targeted and survey observations may be a singular probe of cosmic plasma in this regime. The morphology of the global Faraday depth enhancement is not uniform and isotropic but rather exhibits the classic morphology of an astrophysical bow shock on the southwest side of the main Fornax cluster, and an extended, swept-back wake on the northeastern side. Our favoured explanation for these phenomena is an ongoing merger between the main cluster and a subcluster to the southwest. The shock’s Mach angle and stand-off distance lead to a self-consistent transonic merger speed with Mach 1.06. The region hosting the Faraday depth enhancement also appears to show a decrement in both total and polarised radio emission compared to the broader field. We evaluate cosmic variance and free-free absorption by a pervasive cold dense gas surrounding NGC 1399 as possible causes but find both explanations unsatisfactory, warranting further observations. Generally, our study illustrates the scientific returns that can be expected from all-sky grids of discrete sources generated by forthcoming all-sky radio surveys.
Publisher: Oxford University Press (OUP)
Date: 28-06-2023
Abstract: We use data from the pilot observations of the EMU/POSSUM surveys to study the ‘missing supernova remnant (SNR) problem’, the discrepancy between the number of Galactic SNRs that have been observed, and the number that are estimated to exist. The Evolutionary Map of the Universe (EMU) and the Polarization Sky Survey of the Universe’s Magnetism (POSSUM) are radio sky surveys that are conducted using the Australian Square Kilometre Array Pathfinder (ASKAP). We report on the properties of seven known SNRs in the joint Galactic pilot field, with an approximate longitude and latitude of 323° ≤ l ≤ 330° and −4° ≤ b ≤ 2°, respectively, and identify 21 SNR candidates. Of these, four have been previously identified as SNR candidates, three were previously listed as a single SNR, 13 have not been previously studied, and one has been studied in the infrared. These are the first discoveries of Galactic SNR candidates with EMU/POSSUM and, if confirmed, they will increase the SNR density in this field by a factor of 4. By comparing our SNR candidates to the known Galactic SNR population, we demonstrate that many of these sources were likely missed in previous surveys due to their small angular size and/or low surface brightness. We suspect that there are SNRs in this field that remain undetected due to limitations set by the local background and confusion with other radio sources. The results of this paper demonstrate the potential of the full EMU/POSSUM surveys to uncover more of the missing Galactic SNR population.
Publisher: American Astronomical Society
Date: 1993
DOI: 10.1086/186695
Publisher: Oxford University Press (OUP)
Date: 07-10-2014
Publisher: EDP Sciences
Date: 20-11-2008
Publisher: American Astronomical Society
Date: 16-07-2012
Publisher: EDP Sciences
Date: 29-06-2012
Publisher: Oxford University Press (OUP)
Date: 12-01-2022
Abstract: Many disc galaxies in clusters have been found with bulges of similar age or younger than their surrounding discs, at odds with field galaxies of similar morphology and their expected inside-out formation. We use the Evolution and Assembly of GaLaxies and their Environments (EAGLE) simulations to test potential origins for this difference in field and cluster galaxies. We find, in agreement with observations, that on average disc-dominated field galaxies in the simulations have older inner regions, while similar galaxies in groups and clusters have similarly aged or younger inner regions. This environmental difference is a result of outside-in quenching of the cluster galaxies. Prior to group/cluster infall, galaxies of a given present-day mass and morphology exhibit a similar evolution in their specific star formation rate (sSFR) profiles. Post-infall, the outer sSFRs of group and cluster galaxies significantly decrease due to interstellar medium stripping, while the central sSFR remains similar to field galaxies. Field disc galaxies instead generally retain radially increasing sSFR profiles. Thus, field galaxies continue to develop negative age gradients (younger discs), while cluster galaxies instead develop positive age gradients (younger bulges).
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2021.59
Abstract: We present the most sensitive and detailed view of the neutral hydrogen ( ${\\rm H\\small I}$ ) emission associated with the Small Magellanic Cloud (SMC), through the combination of data from the Australian Square Kilometre Array Pathfinder (ASKAP) and Parkes (Murriyang), as part of the Galactic Australian Square Kilometre Array Pathfinder (GASKAP) pilot survey. These GASKAP-HI pilot observations, for the first time, reveal ${\\rm H\\small I}$ in the SMC on similar physical scales as other important tracers of the interstellar medium, such as molecular gas and dust. The resultant image cube possesses an rms noise level of 1.1 K ( $1.6\\,\\mathrm{mJy\\ beam}^{-1}$ ) $\\mathrm{per}\\ 0.98\\,\\mathrm{km\\ s}^{-1}$ spectral channel with an angular resolution of $30^{\\prime\\prime}$ ( ${\\sim}10\\,\\mathrm{pc}$ ). We discuss the calibration scheme and the custom imaging pipeline that utilises a joint deconvolution approach, efficiently distributed across a computing cluster, to accurately recover the emission extending across the entire ${\\sim}25\\,\\mathrm{deg}^2$ field-of-view. We provide an overview of the data products and characterise several aspects including the noise properties as a function of angular resolution and the represented spatial scales by deriving the global transfer function over the full spectral range. A preliminary spatial power spectrum analysis on in idual spectral channels reveals that the power law nature of the density distribution extends down to scales of 10 pc. We highlight the scientific potential of these data by comparing the properties of an outflowing high-velocity cloud with previous ASKAP+Parkes ${\\rm H\\small I}$ test observations.
Publisher: EDP Sciences
Date: 03-2022
DOI: 10.1051/0004-6361/202142575
Abstract: Aims. Revealing the 3D dynamics of H II region bubbles and their associated molecular clouds and H I envelopes is important for developing an understanding of the longstanding problem as to how stellar feedback affects the density structure and kinematics of the different phases of the interstellar medium. Methods. We employed observations of the H II region RCW 120 in the [C II ] 158 μm line, observed within the Stratospheric Observatory for Infrared Astronomy (SOFIA) legacy program FEEDBACK, and in the 12 CO and 13 CO (3 →2) lines, obtained with the Atacama Pathfinder Experiment (APEX) to derive the physical properties of the gas in the photodissociation region (PDR) and in the molecular cloud. We used high angular resolution H I data from the Southern Galactic Plane Survey to quantify the physical properties of the cold atomic gas through H I self-absorption. The high spectral resolution of the heterodyne observations turns out to be essential in order to analyze the physical conditions, geometry, and overall structure of the sources. Two types of radiative transfer models were used to fit the observed [C II ] and CO spectra. A line profile analysis with the 1D non-LTE radiative transfer code SimLine proves that the CO emission cannot stem from a spherically symmetric molecular cloud configuration. With a two-layer multicomponent model, we then quantified the amount of warm background and cold foreground gas. To fully exploit the spectral-spatial information in the CO spectra, a Gaussian mixture model was introduced that allows for grouping spectra into clusters with similar properties. Results. The CO emission arises mostly from a limb-brightened, warm molecular ring, or more specifically a torus when extrapolated in 3D. There is a deficit of CO emission along the line-of-sight toward the center of the H II region which indicates that the H II region is associated with a flattened molecular cloud. Self-absorption in the CO line may hide signatures of infalling and expanding molecular gas. The [C II ] emission arises from an expanding [C II ] bubble and from the PDRs in the ring/torus. A significant part of [C II ] emission is absorbed in a cool (~60–100 K), low-density ( cm −3 ) atomic foreground layer with a thickness of a few parsec. Conclusions. We propose that the RCW 120 H II region formed in a flattened, filamentary, or sheet-like, molecular cloud and is now bursting out of its parental cloud. The compressed surrounding molecular layer formed a torus around the spherically expanding H II bubble. This scenario can possibly be generalized for other H II bubbles and would explain the observed “flat” structure of molecular clouds associated with H II bubbles. We suggest that the [C II ] absorption observed in many star-forming regions is at least partly caused by low-density, cool, H I -envelopes surrounding the molecular clouds.
Publisher: Elsevier BV
Date: 2021
Publisher: Oxford University Press (OUP)
Date: 07-2005
Publisher: American Astronomical Society
Date: 03-2023
Abstract: We present multiwavelength time-series spectroscopy of SN 2013aa and SN 2017cbv, two Type Ia supernovae (SNe Ia) on the outskirts of the same host galaxy, NGC 5643. This work utilizes new nebular-phase near-infrared (NIR) spectra obtained by the Carnegie Supernova Project-II, in addition to previously published optical and NIR spectra. Using nebular-phase [Fe ii ] lines in the optical and NIR, we examine the explosion kinematics and test the efficacy of several common emission-line-fitting techniques. The NIR [Fe ii ] 1.644 μ m line provides the most robust velocity measurements against variations due to the choice of the fit method and line blending. The resulting effects on velocity measurements due to choosing different fit methods, initial fit parameters, continuum and line profile functions, and fit region boundaries were also investigated. The NIR [Fe ii ] velocities yield the same radial shift direction as velocities measured using the optical [Fe ii ] λ 7155 line, but the sizes of the shifts are consistently and substantially lower, pointing to a potential issue in optical studies. The NIR [Fe ii ] 1.644 μ m emission profile shows a lack of significant asymmetry in both SNe, and the observed low velocities elevate the importance for correcting for any velocity contribution from the host galaxy’s rotation. The low [Fe ii ] velocities measured in the NIR at nebular phases disfavor progenitor scenarios in close double-degenerate systems for both SN 2013aa and SN 2017cbv. The time evolution of the NIR [Fe ii ] 1.644 μ m line also indicates moderately high progenitor white dwarf central density and potentially high magnetic fields.
Publisher: Oxford University Press (OUP)
Date: 12-02-2016
Publisher: Oxford University Press (OUP)
Date: 31-08-2020
Abstract: We have used the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope to search for intervening 21 cm neutral hydrogen (H i) absorption along the line of sight to 53 bright radio continuum sources. Our observations are sensitive to H i column densities typical of D ed Lyman Alpha absorbers (DLAs) in cool gas with an H i spin temperature below about 300–500 K. The six-dish Boolardy Engineering Test Array (BETA) and twelve-antenna Early Science array (ASKAP-12) covered a frequency range corresponding to redshift 0.4 & z & 1.0 and 0.37 & z & 0.77, respectively, for the H i line. Fifty of the 53 radio sources observed have reliable optical redshifts, giving a total redshift path Δz = 21.37. This was a spectroscopically untargeted survey, with no prior assumptions about the location of the lines in redshift space. Four intervening H i lines were detected, two of them new. In each case, the estimated H i column density lies above the DLA limit for H i spin temperatures above 50–80 K, and we estimate a DLA number density at redshift z ∼ 0.6 of $n(z)=0.19^{+0.15 }_{ -0.09}$. This value lies somewhat above the general trend of n(z) with redshift seen in optical DLA studies. Although the current s le is small, it represents an important proof of concept for the much larger 21 cm First Large Absorption Survey in H i (FLASH) project to be carried out with the full 36-antenna ASKAP telescope, probing a total redshift path $\\Delta z\\sim \\, 50,000$.
Publisher: American Astronomical Society
Date: 08-12-2010
Publisher: American Astronomical Society
Date: 20-10-1999
DOI: 10.1086/307854
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.29
Abstract: We present a comparison between the performance of a selection of source finders (SFs) using a new software tool called Hydra. The companion paper, Paper I, introduced the Hydra tool and demonstrated its performance using simulated data. Here we apply Hydra to assess the performance of different source finders by analysing real observational data taken from the Evolutionary Map of the Universe (EMU) Pilot Survey. EMU is a wide-field radio continuum survey whose primary goal is to make a deep ( $20\\mu$ Jy/beam RMS noise), intermediate angular resolution ( $15^{\\prime\\prime}$ ), 1 GHz survey of the entire sky south of $+30^{\\circ}$ declination, and expecting to detect and catalogue up to 40 million sources. With the main EMU survey it is highly desirable to understand the performance of radio image SF software and to identify an approach that optimises source detection capabilities. Hydra has been developed to refine this process, as well as to deliver a range of metrics and source finding data products from multiple SFs. We present the performance of the five SFs tested here in terms of their completeness and reliability statistics, their flux density and source size measurements, and an exploration of case studies to highlight finder-specific limitations.
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.28
Abstract: We investigate the ersity in the sizes and average surface densities of the neutral atomic hydrogen (H i ) gas discs in $\\sim$ 280 nearby galaxies detected by the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY). We combine the uniformly observed, interferometric H i data from pilot observations of the Hydra cluster and NGC 4636 group fields with photometry measured from ultraviolet, optical, and near-infrared imaging surveys to investigate the interplay between stellar structure, star formation, and H i structural parameters. We quantify the H i structure by the size of the H i relative to the optical disc and the average H i surface density measured using effective and isodensity radii. For galaxies resolved by $ $ $1.3$ beams, we find that galaxies with higher stellar masses and stellar surface densities tend to have less extended H i discs and lower H i surface densities: the isodensity H i structural parameters show a weak negative dependence on stellar mass and stellar mass surface density. These trends strengthen when we limit our s le to galaxies resolved by $ $ 2 beams. We find that galaxies with higher H i surface densities and more extended H i discs tend to be more star forming: the isodensity H i structural parameters have stronger correlations with star formation. Normalising the H i disc size by the optical effective radius (instead of the isophotal radius) produces positive correlations with stellar masses and stellar surface densities and removes the correlations with star formation. This is due to the effective and isodensity H i radii increasing with mass at similar rates while, in the optical, the effective radius increases slower than the isophotal radius. Our results are in qualitative agreement with previous studies and demonstrate that with WALLABY we can begin to bridge the gap between small galaxy s les with high spatial resolution H i data and large, statistical studies using spatially unresolved, single-dish data.
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.27
Abstract: The putative host galaxy of FRB 20171020A was first identified as ESO 601-G036 in 2018, but as no repeat bursts have been detected, direct confirmation of the host remains elusive. In light of recent developments in the field, we re-examine this host and determine a new association confidence level of 98%. At 37 Mpc, this makes ESO 601-G036 the third closest FRB host galaxy to be identified to date and the closest to host an apparently non-repeating FRB (with an estimated repetition rate limit of $ $ $0.011$ bursts per day above $10^{39}$ erg). Due to its close distance, we are able to perform detailed multi-wavelength analysis on the ESO 601-G036 system. Follow-up observations confirm ESO 601-G036 to be a typical star-forming galaxy with H i and stellar masses of $\\log_{10}\\!(M_{\\rm{H\\,{\\small I}}} / M_\\odot) \\sim 9.2$ and $\\log_{10}\\!(M_\\star / M_\\odot) = 8.64^{+0.03}_{-0.15}$ , and a star formation rate of $\\text{SFR} = 0.09 \\pm 0.01\\,{\\rm M}_\\odot\\,\\text{yr}^{-1}$ . We detect, for the first time, a diffuse gaseous tail ( $\\log_{10}\\!(M_{\\rm{H\\,{\\small I}}} / M_\\odot) \\sim 8.3$ ) extending to the south-west that suggests recent interactions, likely with the confirmed nearby companion ESO 601-G037. ESO 601-G037 is a stellar shred located to the south of ESO 601-G036 that has an arc-like morphology, is about an order of magnitude less massive, and has a lower gas metallicity that is indicative of a younger stellar population. The properties of the ESO 601-G036 system indicate an ongoing minor merger event, which is affecting the overall gaseous component of the system and the stars within ESO 601-G037. Such activity is consistent with current FRB progenitor models involving magnetars and the signs of recent interactions in other nearby FRB host galaxies.
Publisher: Oxford University Press (OUP)
Date: 11-04-2022
Abstract: We present the Australian Square Kilometre Array Pathfinder (ASKAP) observations of the Galaxy and Mass Assembly (GAMA)-23h field. The survey was carried out at 887.5 MHz and covers an ∼83 square deg field. We imaged the calibrated visibility data, taken as part of the Evolutionary Mapping of Universe Early Science Programme, using the latest version of the ASKAPSoft pipeline. The final mosaic has an angular resolution of 10 arcsec and a central rms noise of around 38 $\\mu$Jy beam−1. The derived radio source catalogue has 39 812 entries above a peak flux density threshold of 5σ. We searched for the radio source host galaxy counterparts using the GAMA spectroscopic (with an i-band magnitude limit of 19.2 mag) and multiwavelength catalogues that are available as part of the collaboration. We identified hosts with GAMA spectroscopic redshifts for 5934 radio sources. We describe the data reduction, imaging, and source identification process, and present the source counts. Thanks to the wide area covered by our survey, we obtain very robust counts down to 0.2 mJy. ASKAP’s exceptional survey speed, providing efficient, sensitive, and high-resolution mapping of large regions of the sky in conjunction with the multiwavelength data available for the GAMA23 field, allowed us to discover 63 giant radio galaxies. The data presented here demonstrate the excellent capabilities of ASKAP in the pre-SKA era.
Publisher: EDP Sciences
Date: 07-2010
Publisher: EDP Sciences
Date: 03-04-2007
Publisher: EDP Sciences
Date: 06-2018
DOI: 10.1051/0004-6361/201732373
Abstract: The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band H α + [NII] imaging survey carried out with MegaCam at the Canada-France-Hawaii Telescope. During pilot observations taken in the spring of 2016 we observed NGC 4330, an intermediate mass ( M * ≃ 10 9.8 M ⊙ ) edge-on star forming spiral currently falling into the core of the Virgo cluster. While previous H α observations showed a clumpy complex of ionised gas knots outside the galaxy disc, new deep observations revealed a low surface brightness ~10 kpc tail exhibiting a peculiar filamentary structure. The filaments are remarkably parallel to one another and clearly indicate the direction of motion of the galaxy in the Virgo potential. Motivated by the detection of these features which indicate ongoing gas stripping, we collected literature photometry in 15 bands from the far-UV to the far-IR and deep optical long-slit spectroscopy using the FORS2 instrument at the ESO Very Large Telescope. Using a newly developed Monte Carlo code that jointly fits spectroscopy and photometry, we reconstructed the star formation histories in apertures along the major axis of the galaxy. Our results have been validated against the output of CIGALE, a fitting code which has been previously used for similar studies. We found a clear outside-in gradient with radius of the time when the quenching event started: the outermost radii were stripped ~500 Myr ago, while the stripping reached the inner 5 kpc from the centre in the last 100 Myr. Regions at even smaller radii are currently still forming stars fueled by the presence of HI and H 2 gas. When compared to statistical studies of the quenching timescales in the local Universe we find that ram pressure stripping of the cold gas is an effective mechanism to reduce the transformation times for galaxies falling into massive clusters. Future systematic studies of all the active galaxies observed by VESTIGE in the Virgo cluster will extend these results to a robust statistical framework.
Publisher: Oxford University Press (OUP)
Date: 21-05-2013
DOI: 10.1093/MNRAS/STT747
Publisher: Cambridge University Press (CUP)
Date: 08-2021
DOI: 10.1017/S1743921322004392
Abstract: At least half of the local galaxies reside in galaxy groups, which indicates that the group is the common environment where galaxies evolve. Therefore, it is important to probe how significantly galaxies are affected by group environmental processes, in order to obtain a better understanding of galaxy evolution. We carried out a new CO imaging survey for 31 galaxies in the IC 1459 and NGC 4636 groups, using the Atacama Compact Array, to study the effect of the group environment on the molecular gas properties and the star formation activity. With our resolved CO data, combined with high-resolution H i images, we find asymmetric CO and H i distributions in the group galaxies. Compared to isolated galaxies, group members have relatively low molecular gas fraction and low star formation rate. These results suggest that the group environment can change the properties of cold gas components and star formation in group galaxies.
Publisher: Oxford University Press (OUP)
Date: 28-02-2023
Abstract: Galaxy morphology in atomic hydrogen (H i) and in the ultraviolet (UV) are closely linked. This has motivated their combined use to quantify morphology over the full H i disc for both H i and UV imaging. We apply galaxy morphometrics: concentration, asymmetry, gini, M20 and multimode-intensity-deviation statistics to the first moment-0 maps of the WALLABY Survey of galaxies in the hydra cluster centre. Taking advantage of this new H i survey, we apply the same morphometrics over the full H i extent on archival GALEX FUV and NUV data to explore how well H i truncated, extended ultraviolet disc (XUV) and other morphological phenomena can be captured using pipeline WALLABY data products. Extended H i and UV discs can be identified relatively straightforward from their respective concentration. Combined with WALLABY H i, even the shallowest GALEX data are sufficient to identify XUV discs. Our second goal is to isolate galaxies undergoing ram-pressure stripping in the H i morphometric space. We employ four different machine learning techniques, a decision tree, a k-nearest neighbour, a support-vector machine, and a random forest. Up to 80 per cent precision and recall are possible with the random forest giving the most robust results.
Publisher: Zenodo
Date: 2019
Publisher: Oxford University Press (OUP)
Date: 24-08-2015
Publisher: Oxford University Press (OUP)
Date: 10-2006
Publisher: American Astronomical Society
Date: 14-09-2012
Publisher: Oxford University Press (OUP)
Date: 09-02-2012
Publisher: Oxford University Press (OUP)
Date: 06-07-2020
Abstract: We report the results of the rapid follow-up observations of gamma-ray bursts (GRBs) detected by the Fermi satellite to search for associated fast radio bursts. The observations were conducted with the Australian Square Kilometre Array Pathfinder at frequencies from 1.2 to 1.4 GHz. A set of 20 bursts, of which four were short GRBs, were followed up with a typical latency of about 1 min, for a duration of up to 11 h after the burst. The data were searched using 4096 dispersion measure trials up to a maximum dispersion measure of 3763 pc cm−3, and for pulse widths w over a range of duration from 1.256 to 40.48 ms. No associated pulsed radio emission was observed above $26 \\, {\\rm Jy\\, ms}\\, (w/1\\, {\\rm ms})^{-1/2}$ for any of the 20 GRBs.
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.48
Publisher: American Astronomical Society
Date: 09-08-2011
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.50
Abstract: We present WALLABY pilot data release 1, the first public release of H i pilot survey data from the Wide-field ASKAP L-band Legacy All-sky Blind Survey (WALLABY) on the Australian Square Kilometre Array Pathfinder. Phase 1 of the WALLABY pilot survey targeted three $60\\,\\mathrm{deg}^{2}$ regions on the sky in the direction of the Hydra and Norma galaxy clusters and the NGC 4636 galaxy group, covering the redshift range of $z \\lesssim 0.08$ . The source catalogue, images and spectra of nearly 600 extragalactic H i detections and kinematic models for 109 spatially resolved galaxies are available. As the pilot survey targeted regions containing nearby group and cluster environments, the median redshift of the s le of $z \\approx 0.014$ is relatively low compared to the full WALLABY survey. The median galaxy H i mass is $2.3 \\times 10^{9}\\,{\\rm M}_{{\\odot}}$ . The target noise level of $1.6\\,\\mathrm{mJy}$ per 30 ′′ beam and $18.5\\,\\mathrm{kHz}$ channel translates into a $5 \\sigma$ H i mass sensitivity for point sources of about $5.2 \\times 10^{8} \\, (D_{\\rm L} / \\mathrm{100\\,Mpc})^{2} \\, {\\rm M}_{{\\odot}}$ across 50 spectral channels ( ${\\approx} 200\\,\\mathrm{km \\, s}^{-1}$ ) and a $5 \\sigma$ H i column density sensitivity of about $8.6 \\times 10^{19} \\, (1 + z)^{4}\\,\\mathrm{cm}^{-2}$ across 5 channels ( ${\\approx} 20\\,\\mathrm{km \\, s}^{-1}$ ) for emission filling the 30 ′′ beam. As expected for a pilot survey, several technical issues and artefacts are still affecting the data quality. Most notably, there are systematic flux errors of up to several 10% caused by uncertainties about the exact size and shape of each of the primary beams as well as the presence of sidelobes due to the finite deconvolution threshold. In addition, artefacts such as residual continuum emission and bandpass ripples have affected some of the data. The pilot survey has been highly successful in uncovering such technical problems, most of which are expected to be addressed and rectified before the start of the full WALLABY survey.
Publisher: Oxford University Press (OUP)
Date: 09-1994
Publisher: American Astronomical Society
Date: 12-2022
Abstract: We conduct a 12 C 16 O( J = 1−0) (hereafter CO) mapping survey of 64 galaxies in the Fornax cluster using the Atacama Large Millimeter/submillimeter Array Morita array in cycle 5. CO emission is detected from 23 out of the 64 galaxies. Our s le includes dwarf, spiral, and elliptical galaxies with stellar masses of M star ∼ 10 6.3−11.6 M ⊙ . The achieved beam size and sensitivity are 15″ × 8″ and ∼12 mJy beam −1 at the velocity resolution of ∼10 km s −1 , respectively. We study the cold gas (molecular and atomic gas) properties of 38 subs les with M star 10 9 M ⊙ combined with literature H i data. We find that (1) the low star formation (SF) activity in the Fornax galaxies is caused by the decrease in the cold gas mass fraction with respect to stellar mass (hereafter, gas fraction) rather than the decrease of the SF efficiency from the cold gas (2) the atomic gas fraction is more heavily reduced than the molecular gas fraction of such galaxies with low SF activity. A comparison between the cold gas properties of the Fornax galaxies and their environmental properties suggests that the atomic gas is stripped tidally and by the ram pressure, which leads to the molecular gas depletion with an aid of the strangulation and consequently SF quenching. Preprocesses in the group environment would also play a role in reducing cold gas reservoirs in some Fornax galaxies.
Publisher: Springer Berlin Heidelberg
Date: 2007
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.24
Abstract: The latest generation of radio surveys are now producing sky survey images containing many millions of radio sources. In this context it is highly desirable to understand the performance of radio image source finder (SF) software and to identify an approach that optimises source detection capabilities. We have created Hydra to be an extensible multi-SF and cataloguing tool that can be used to compare and evaluate different SFs. Hydra, which currently includes the SFs Aegean, Caesar, ProFound, PyBDSF, and Selavy, provides for the addition of new SFs through containerisation and configuration files. The SF input RMS noise and island parameters are optimised to a 90% ‘percentage real detections’ threshold (calculated from the difference between detections in the real and inverted images), to enable comparison between SFs. Hydra provides completeness and reliability diagnostics through observed-deep ( $\\mathcal{D}$ ) and generated-shallow ( $\\mathcal{S}$ ) images, as well as other statistics. In addition, it has a visual inspection tool for comparing residual images through various selection filters, such as S/N bins in completeness or reliability. The tool allows the user to easily compare and evaluate different SFs in order to choose their desired SF, or a combination thereof. This paper is part one of a two part series. In this paper we introduce the Hydra software suite and validate its $\\mathcal{D/S}$ metrics using simulated data. The companion paper demonstrates the utility of Hydra by comparing the performance of SFs using both simulated and real images.
Publisher: Oxford University Press (OUP)
Date: 09-2015
Publisher: American Astronomical Society
Date: 07-2021
Abstract: This study uses H i image data from the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY) pilot survey with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, covering the Hydra cluster out to 2.5 r 200 . We present the projected phase–space distribution of H i -detected galaxies in Hydra, and identify that nearly two-thirds of the galaxies within 1.25 r 200 may be in the early stages of ram pressure stripping. More than half of these may be only weakly stripped, with the ratio of strippable H i (i.e., where the galactic restoring force is lower than the ram pressure in the disk) mass fraction (over total H i mass) distributed uniformly below 90%. Consequently, the H i mass is expected to decrease by only a few 0.1 dex after the currently strippable portion of H i in these systems has been stripped. A more detailed look at the subset of galaxies that are spatially resolved by WALLABY observations shows that, while it typically takes less than 200 Myr for ram pressure stripping to remove the currently strippable portion of H i , it may take more than 600 Myr to significantly change the total H i mass. Our results provide new clues to understanding the different rates of H i depletion and star formation quenching in cluster galaxies.
Publisher: Oxford University Press (OUP)
Date: 30-04-2021
Abstract: We present the discovery of another odd radio circle (ORC) with the Australian Square Kilometre Array Pathfinder (ASKAP) at 944 MHz. The observed radio ring, ORC J0102–2450, has a diameter of ∼70 arcsec or 300 kpc, if associated with the central elliptical galaxy DES J010224.33–245039.5 (z ∼ 0.27). Considering the overall radio morphology (circular ring and core) and lack of ring emission at non-radio wavelengths, we investigate if ORC J0102–2450 could be the relic lobe of a giant radio galaxy seen end on or the result of a giant blast wave. We also explore possible interaction scenarios, for ex le, with the companion galaxy, DES J010226.15–245104.9, located in or projected on to the south-eastern part of the ring. We encourage the search for further ORCs in radio surveys to study their properties and origin.
Publisher: EDP Sciences
Date: 29-11-2006
Publisher: Oxford University Press (OUP)
Date: 09-12-2021
Abstract: We present neutral hydrogen (H i) absorption spectra of the black hole candidate X-ray binary (XRB) MAXI J1348–630 using the Australian Square Kilometre Array Pathfinder (ASKAP) and MeerKAT. The ASKAP H i spectrum shows a maximum negative radial velocity (with respect to the local standard of rest) of −31 ± 4 km s−1 for MAXI J1348–630, as compared to −50 ± 4 km s−1 for a stacked spectrum of several nearby extragalactic sources. This implies a most probable distance of $2.2^{+0.5}_{-0.6}$ kpc for MAXI J1348–630, and a strong upper limit of the tangent point distance at 5.3 ± 0.1 kpc. Our preferred distance implies that MAXI J1348–630 reached 17 ± 10 per cent of the Eddington luminosity at the peak of its outburst, and that the source transited from the soft to the hard X-ray spectral state at 2.5 ± 1.5 per cent of the Eddington luminosity. The MeerKAT H i spectrum of MAXI J1348–630 (obtained from the older, low-resolution 4k mode) is consistent with the re-binned ASKAP spectrum, highlighting the potential of the eventual capabilities of MeerKAT for XRB spectral line studies.
Publisher: American Astronomical Society
Date: 09-02-2016
Publisher: Oxford University Press (OUP)
Date: 27-08-2012
Publisher: Oxford University Press (OUP)
Date: 02-2008
Publisher: American Astronomical Society
Date: 11-02-2008
Publisher: Oxford University Press (OUP)
Date: 12-11-2022
Abstract: The dwarf irregular galaxy HIPASS J1131-31 was discovered as a source of HI emission at low redshift in such close proximity of a bright star that we call it Peekaboo. The galaxy resolves into stars in images with Hubble Space Telescope, leading to a distance estimate of 6.8 ± 0.7 Mpc. Spectral optical observations with the Southern African Large Telescope reveal HIPASS J1131-31 to be one of the most extremely metal-poor galaxies known with the gas-phase oxygen abundance 12 + log(O/H) = 6.99 ± 0.16 dex via the direct [O iii] 4363 line method and 6.87 ± 0.07 dex from the two strong line empirical methods. The red giant branch of the system is tenuous compared with the prominence of the features of young populations in the colour-magnitude diagram, inviting speculation that star formation in the galaxy only began in the last few Gyr.
Publisher: Oxford University Press (OUP)
Date: 23-11-2021
Abstract: The Magellanic Clouds are the only external galaxies known to host radio pulsars. The dispersion and rotation measures of pulsars in the Clouds can aid in understanding their structure, and studies of the pulsars themselves can point to potential differences between them and their Galactic counterparts. We use the high sensitivity of the MeerKAT telescope to observe 17 pulsars in the Small and Large Magellanic Clouds in addition to five foreground (Galactic) pulsars. We provide polarisation profiles for 18 of these pulsars, improved measurements of their dispersion and rotation measures, and derive the mean parallel magnetic field along the lines of sight. The results are broadly in agreement with expectations for the structure and strength of the magnetic field in the Large and Small Magellanic Clouds. The Magellanic Cloud pulsars have profiles which are narrower than expected from the period-width relationship and we show this is due to selection effects in pulsar surveys rather than any intrinsic difference between the population of Galactic and Magellanic objects.
Publisher: American Astronomical Society
Date: 07-1995
DOI: 10.1086/117507
Publisher: EDP Sciences
Date: 09-2005
Publisher: American Astronomical Society
Date: 07-2004
DOI: 10.1086/421744
Publisher: Oxford University Press (OUP)
Date: 22-02-2022
Abstract: Low- and intermediate-mass stars end their life dispersing their outer layers into the circumstellar medium, during the asymptotic and post-asymptotic giant branch phases. OH masers at 18 cm offer an effective way to probe their circumstellar environment. In this work, we present the discovery of seven OH maser sources likely associated with such evolved stars from the visual inspection of Australian SKA Pathfinder (ASKAP) continuum images. These seven sources do not emit real continuum emission, but the high sensitivity of our images allows us to detect their maser emission, resembling continuum sources. To confirm their nature, we carried out spectral-line observations with ATCA. All the sources showed the double-peaked spectra at 1612 MHz, typical of evolved stars. The detection of maser emission in continuum images can be a complementary and easy-to-use method to discover new maser sources with the large-area deep surveys conducted with the Square Kilometre Array (SKA) precursors. The implication for radio stars studies are remarkable since pure OH maser sources (i.e. with no continuum associated) represent, at a sensitivity of $100\\,\\mu \\mathrm{Jy\\,beam}^{-1}$, about 4 per cent of all Galactic sources and by far the most numerous stellar population.
Publisher: American Astronomical Society
Date: 08-2002
DOI: 10.1086/341582
Publisher: Springer Science and Business Media LLC
Date: 2003
Publisher: American Astronomical Society
Date: 07-2002
DOI: 10.1086/340491
Publisher: American Astronomical Society
Date: 06-2003
DOI: 10.1086/374944
Publisher: Oxford University Press (OUP)
Date: 07-04-2022
Abstract: Observations of the neutral atomic hydrogen (H i) in the nuclear starburst galaxy NGC 4945 with MeerKAT are presented. We find a large amount of halo gas, previously missed by H i observations, accounting for 6.8 per cent of the total H i mass. This is most likely gas blown into the halo by star formation. Our maps go down to a 3σ column density level of 5 × 1018 cm−2. We model the H i distribution using tilted-ring fitting techniques and find a warp on the galaxy’s approaching and receding sides. The H i in the northern side of the galaxy appears to be suppressed. This may be the result of ionization by the starburst activity in the galaxy, as suggested by a previous study. The origin of the warp is unclear but could be due to past interactions or ram pressure stripping. Broad, asymmetric H i absorption lines extending throughout the H i emission velocity channels are present towards the nuclear region of NGC 4945. Such broad lines suggest the existence of a nuclear ring moving at a high circular velocity. This is supported by the clear rotation patterns in the H i absorption velocity field. The asymmetry of the absorption spectra can be caused by outflows or inflows of gas in the nuclear region of NGC 4945. The continuum map shows small extensions on both sides of the galaxy’s major axis that might be signs of outflows resulting from the starburst activity.
Publisher: Oxford University Press (OUP)
Date: 08-2019
DOI: 10.1093/PASJ/PSZ067
Abstract: We present the results of 12CO(J = 1–0) mosaicing observations of the cD galaxy NGC 1316 at kiloparsec resolution performed with the Morita Array of the Atacama Large Millimeter/submillimeter Array (ALMA). We reveal the detailed distribution of the molecular gas in the central region for the first time: a shell structure in the northwest, a barely resolved blob in the southeast of the center, and some clumps between them. The total molecular gas mass obtained with a standard Milky Way CO-to-H2 conversion factor is $(5.62 \\pm 0.53) \\times 10^{8}\\, M_{\\odot }$, which is consistent with previous studies. The disturbed velocity field of the molecular gas suggests that the molecular gas was injected very recently ( Gyr) if it has an external origin, and is in the process of settling into a rotating disk. Assuming that a low-mass gas-rich galaxy has accreted, the gas-to-dust ratio and H2-to-H i ratio are unusually low (∼28) and high (∼5.6), respectively. To explain these ratios additional processes should be taken into account, such as effective dust formation and conversion from atomic to molecular gas during the interaction. We also discuss the interaction between the nuclear jet and the molecular gas.
Publisher: EDP Sciences
Date: 2018
DOI: 10.1051/0004-6361/201526384
Abstract: Context. The initial conditions of molecular clumps in which high-mass stars form are poorly understood. In particular, a more detailed study of the earliest evolutionary phases is needed. The APEX Telescope Large Area Survey of the whole inner Galactic disk at 870 μ m, ATLASGAL, has therefore been conducted to discover high-mass star-forming regions at different evolutionary phases. Aims. We derive properties such as velocities, rotational temperatures, column densities, and abundances of a large s le of southern ATLASGAL clumps in the fourth quadrant. Methods. Using the Parkes telescope, we observed the NH 3 (1, 1) to (3, 3) inversion transitions towards 354 dust clumps detected by ATLASGAL within a Galactic longitude range between 300° and 359° and a latitude within ± 1.5°. For a subs le of 289 sources, the N 2 H + (1–0) line was measured with the Mopra telescope. Results. We measured a median NH 3 (1, 1) line width of ~ 2 km s -1 , rotational temperatures from 12 to 28 K with a mean of 18 K, and source-averaged NH 3 abundances from 1.6 × 10 -6 to 10 -8 . For a subs le with detected NH 3 (2, 2) hyperfine components, we found that the commonly used method to compute the (2, 2) optical depth from the (1, 1) optical depth and the (2, 2) to (1, 1) main beam brightness temperature ratio leads to an underestimation of the rotational temperature and column density. A larger median virial parameter of ~ 1 is determined using the broader N 2 H + line width than is estimated from the NH 3 line width of ~ 0.5 with a general trend of a decreasing virial parameter with increasing gas mass. We obtain a rising NH 3 (1, 1)/N 2 H + line-width ratio with increasing rotational temperature. Conclusions. A comparison of NH 3 line parameters of ATLASGAL clumps to cores in nearby molecular clouds reveals smaller velocity dispersions in low-mass than high-mass star-forming regions and a warmer surrounding of ATLASGAL clumps than the surrounding of low-mass cores. The NH 3 (1, 1) inversion transition of 49% of the sources shows hyperfine structure anomalies. The intensity ratio of the outer hyperfine structure lines with a median of 1.27 ± 0.03 and a standard deviation of 0.45 is significantly higher than 1, while the intensity ratios of the inner satellites with a median of 0.9 ± 0.02 and standard deviation of 0.3 and the sum of the inner and outer hyperfine components with a median of 1.06 ± 0.02 and standard deviation of 0.37 are closer to 1.
Publisher: American Astronomical Society
Date: 10-2023
Publisher: Oxford University Press (OUP)
Date: 22-12-2019
Publisher: American Astronomical Society
Date: 12-1998
DOI: 10.1086/300633
Publisher: Oxford University Press (OUP)
Date: 21-12-2009
Publisher: EDP Sciences
Date: 23-03-2017
DOI: 10.1051/0004-6361/201629300
Abstract: Do some environments favor efficient conversion of molecular gas into stars? To answer this, we need to be able to estimate the H 2 mass. Traditionally, this is done using CO observations and a few assumptions but the Herschel observations which cover the far-IR dust spectrum make it possible to estimate the molecular gas mass independently of CO and thus to investigate whether and how the CO traces H 2 . Previous attempts to derive gas masses from dust emission suffered from biases. Generally, dust surface densities, H i column densities, and CO intensities are used to derive a gas-to-dust ratio (GDR) and the local CO intensity to H 2 column density ratio ( X CO ), sometimes allowing for an additional CO-dark gas component ( K dark ). We tested earlier methods, revealing degeneracies among the parameters, and then used a sophisticated Bayesian formalism to derive the most likely values for each of the parameters mentioned above as a function of position in the nearby prototypical low metallicity (12 + log (O/H) ~ 8.4) spiral galaxy M 33. The data are from the IRAM Large Program mapping in the CO(2–1) line along with high-resolution H i and Herschel dust continuum observations. Solving for GDR, X CO , and K dark in macropixels 500 pc in size, each containing many in idual measurements of the CO, H i , and dust emission, we find that (i) allowing for CO dark gas ( K dark ) significantly improves fits (ii) K dark decreases with galactocentric distance (iii) GDR is slightly higher than initially expected and increases with galactocentric distance (iv) the total amount of dark gas closely follows the radially decreasing CO emission, as might be expected if the dark gas is H 2 where CO is photodissociated. The total amount of H 2 , including dark gas, yields an average X CO of twice the galactic value of 2 × 10 20 cm -2 / K km s -1 , with about 55% of this traced directly through CO. The rather constant fraction of dark gas suggests that there is no large population of diffuse H 2 clouds (unrelated to GMCs) without CO emission. Unlike in large spirals, we detect no systematic radial trend in X CO , possibly linked to the absence of a radial decrease in CO line ratios.
Publisher: EDP Sciences
Date: 28-07-2009
Publisher: American Astronomical Society
Date: 22-05-2017
Publisher: Cambridge University Press (CUP)
Date: 08-2012
DOI: 10.1017/S1743921313000926
Abstract: HI absorption-line studies provide a unique probe of the gas distribution and kinematics in galaxies well beyond the local universe ( z ≳ 0.3). HI absorption-line surveys with next-generation radio telescopes will provide the first large-scale studies of HI in a redshift regime which is poorly understood. However, we currently lack the understanding to infer galaxy properties from absorption-line observations alone. To address this issue, we are conducting a search for intervening HI absorption in a s le of 20 nearby galaxies. Our aim is to investigate how the detection rate varies with distance from the galaxy. We target sight-lines to bright continuum sources, which intercept known gas-rich galaxies, selected from the HIPASS Bright Galaxy Catalogue (Koribalski et al. 2004). In our pilot s le, six galaxies with impact parameters 20 kpc, we do not detect any absorption lines — although all are detected in 21cm emission. This indicates that an absorption non-detection cannot simply be interpreted as an absence of neutral gas – see Fig. 1. Our detection rate is low compared to previous surveys e.g. Gupta et al. (2010). This is, at least partially, due to the high resolution of the observations reducing the flux of the background source, which will also be an issue in future surveys, such as ASKAP-FLASH.
Publisher: Oxford University Press (OUP)
Date: 12-04-2018
DOI: 10.1093/MNRAS/STY741
Publisher: Oxford University Press (OUP)
Date: 11-05-2016
Publisher: Oxford University Press (OUP)
Date: 08-2022
Abstract: Abell 3266 is a massive and complex merging galaxy cluster that exhibits significant substructure. We present new, highly sensitive radio continuum observations of Abell 3266 performed with the Australian Square Kilometre Array Pathfinder (0.8–1.1 GHz) and the Australia Telescope Compact Array (1.1–3.1 GHz). These deep observations provide new insights into recently reported diffuse non-thermal phenomena associated with the intracluster medium, including a ‘wrong-way’ relic, a fossil plasma source, and an as-yet unclassified central diffuse ridge, which we reveal comprises the brightest part of a large-scale radio halo detected here for the first time. The ‘wrong-way’ relic is highly atypical of its kind: it exhibits many classical signatures of a shock-related radio relic, while at the same time exhibiting strong spectral steepening. While radio relics are generally consistent with a quasi-stationary shock scenario, the ‘wrong-way’ relic is not. We study the spectral properties of the fossil plasma source it exhibits an ultrasteep and highly curved radio spectrum, indicating an extremely aged electron population. The larger scale radio halo fills much of the cluster centre, and presents a strong connection between the thermal and non-thermal components of the intracluster medium, along with evidence of substructure. Whether the central diffuse ridge is simply a brighter component of the halo, or a mini-halo, remains an open question. Finally, we study the morphological and spectral properties of the multiple complex radio galaxies in this cluster in unprecedented detail, tracing their evolutionary history.
Publisher: Oxford University Press (OUP)
Date: 07-2003
Publisher: Oxford University Press (OUP)
Date: 17-07-2014
Publisher: Oxford University Press (OUP)
Date: 22-09-2018
Publisher: AIP
Date: 2008
DOI: 10.1063/1.2973559
Publisher: EDP Sciences
Date: 10-2015
Publisher: American Astronomical Society
Date: 19-09-2007
DOI: 10.1086/521925
Publisher: American Astronomical Society
Date: 23-09-2008
DOI: 10.1086/592784
Publisher: Oxford University Press (OUP)
Date: 24-03-2022
Abstract: Odd radio circles (ORCs) are recently-discovered faint diffuse circles of radio emission, of unknown cause, surrounding galaxies at moderate redshift (z ∼ 0.2 – 0.6). Here, we present detailed new MeerKAT radio images at 1284 MHz of the first ORC, originally discovered with the Australian Square Kilometre Array Pathfinder, with higher resolution (6 arcsec) and sensitivity (∼ 2.4 μJy/beam). In addition to the new images, which reveal a complex internal structure consisting of multiple arcs, we also present polarization and spectral index maps. Based on these new data, we consider potential mechanisms that may generate the ORCs.
Publisher: EDP Sciences
Date: 31-10-2013
Publisher: Springer New York
Date: 2010
Publisher: American Astronomical Society
Date: 03-2022
Abstract: We study the tidal interaction of galaxies in the Eridanus supergroup, using H i data from the pre-pilot survey of the Widefield ASKAP L -band Legacy All-sky Blind surveY. We obtain optical photometric measurements and quantify the strength of tidal perturbation using a tidal parameter S sum . For low-mass galaxies of M * ≲ 10 9 M ⊙ , we find a dependence of decreasing H i to optical disk size ratio with increasing S sum , but no dependence of H i spectral line asymmetry with S sum . This is consistent with the behavior expected under tidal stripping. We confirm that the color profile shape and color gradient depend on the stellar mass, but there is an additional correlation of low-mass galaxies having their color gradients within 2 R 50 increasing with higher S sum . For these low-mass galaxies, the dependence of color gradients on S sum is driven by the color becoming progressively redder in the inner disk when tidal perturbations are stronger. For high-mass galaxies, there is no dependence of color gradients on S sum , and we find a marginal reddening throughout the disks with increasing S sum . Our result highlights tidal interaction as an important environmental effect in producing the faint end of the star formation suppressed sequence in galaxy groups.
Publisher: Oxford University Press (OUP)
Date: 15-10-2010
Publisher: American Astronomical Society
Date: 09-1995
DOI: 10.1086/176140
Publisher: Oxford University Press (OUP)
Date: 02-07-2021
Abstract: We present an analysis of a new 120 deg2 radio continuum image of the Large Magellanic Cloud (LMC) at 888 MHz with a bandwidth of 288 MHz and beam size of 13${_{.}^{\\prime\\prime}}$9 × 12${_{.}^{\\prime\\prime}}$1 from the Australian Square Kilometre Array Pathfinder processed as part of the Evolutionary Map of the Universe survey. The median root mean squared noise is 58 $\\mu$Jy beam−1. We present a catalogue of 54 612 sources, ided over a Gold list (30 866 sources) complete down to 0.5 mJy uniformly across the field, a Silver list (22 080 sources) reaching down to & .2 mJy, and a Bronze list (1666 sources) of visually inspected sources in areas of high noise and/or near bright complex emission. We discuss detections of planetary nebulae and their radio luminosity function, young stellar objects showing a correlation between radio luminosity and gas temperature, novae and X-ray binaries in the LMC, and active stars in the Galactic foreground that may become a significant population below this flux level. We present ex les of diffuse emission in the LMC (H ii regions, supernova remnants, bubbles) and distant galaxies showcasing spectacular interaction between jets and intracluster medium. Among 14 333 infrared counterparts of the predominantly background radio source population, we find that star-forming galaxies become more prominent below 3 mJy compared to active galactic nuclei. We combine the new 888 MHz data with archival Australia Telescope Compact Array data at 1.4 GHz to determine spectral indices the vast majority display synchrotron emission but flatter spectra occur too. We argue that the most extreme spectral index values are due to variability.
Publisher: Oxford University Press (OUP)
Date: 10-08-2021
Abstract: We present the Australian Square Kilometre Array Pathfinder (ASKAP) WALLABY pre-pilot observations of two ‘dark’ H i sources (with H i masses of a few times 108 $\\rm {M}_\\odot$ and no known stellar counterpart) that reside within 363 kpc of NGC 1395, the most massive early-type galaxy in the Eridanus group of galaxies. We investigate whether these ‘dark’ H i sources have resulted from past tidal interactions or whether they are an extreme class of low surface brightness galaxies. Our results suggest that both scenarios are possible, and not mutually exclusive. The two ‘dark’ H i sources are compact, reside in relative isolation, and are more than 159 kpc away from their nearest H i-rich galaxy neighbour. Regardless of origin, the H i sizes and masses of both ‘dark’ H i sources are consistent with the H i size–mass relationship that is found in nearby low-mass galaxies, supporting the possibility that these H i sources are an extreme class of low surface brightness galaxies. We identified three analogues of candidate primordial ‘dark’ H i galaxies within the TNG100 cosmological, hydrodynamic simulation. All three model analogues are dark matter dominated, have assembled most of their mass 12–13 Gyr ago, and have not experienced much evolution until cluster infall 1–2 Gyr ago. Our WALLABY pre-pilot science results suggest that the upcoming large-area H i surveys will have a significant impact on our understanding of low surface brightness galaxies and the physical processes that shape them.
Publisher: American Astronomical Society
Date: 25-04-2014
Publisher: American Astronomical Society
Date: 02-1997
DOI: 10.1086/118278
Publisher: American Astronomical Society
Date: 10-2002
DOI: 10.1086/342546
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2020.52
Abstract: We have found a class of circular radio objects in the Evolutionary Map of the Universe Pilot Survey, using the Australian Square Kilometre Array Pathfinder telescope. The objects appear in radio images as circular edge-brightened discs, about one arcmin diameter, that are unlike other objects previously reported in the literature. We explore several possible mechanisms that might cause these objects, but none seems to be a compelling explanation.
Publisher: Oxford University Press (OUP)
Date: 14-06-2010
Publisher: Elsevier BV
Date: 06-1997
DOI: 10.1016/S0748-7983(97)92364-7
Abstract: This study aims to update the experience of multimodality approaches in the management of oesophageal cancer that have been adopted in several Australian and New Zealand hospitals. Between 1984 and 1985, 92 patients received pre-operative radiotherapy (30-36 Gy over 3 weeks) and one of two chemotherapy regimes (one or two courses of i.v. cisplatin 80 mg/m2 plus a 4-5 day continuous i.v. of fluorouracil 5-800 mg/m2/day) concurrently prior to surgery. Eighty-two patients (89%) underwent resection as planned. Operative specimens were microscopically free of residual tumour in 18 patients. Eight patients (9%) had treatment-related deaths: seven from surgery and one due to pre-operative chemoradiation. The Kaplan-Meier 5-year cause-specific survival estimates were 32.9 +/- 7.8% for the 58 patients with squamous cancer and 0% for the 32 with adenocarcinoma. Complete pathological response to the pre-operative regime was more common in females and was associated with a survival advantage. Five-year cause-specific survival expectation in patients who experienced a complete pathological response was 71.5 +/- 12.4%, whereas it was only 15.9 +/- 5.6% in patients who had residual cancer in their surgical specimens. Although less toxic the pre-operative regime utilizing only one cycle of chemotherapy was no less efficacious either in producing a complete pathological response or in terms of survival expectation. This uncontrolled pilot study has produced encouraging long-term results, especially for patients with squamous carcinoma that experienced a complete response to pre-operative synchronous chemoradiotherapy. A randomized controlled study comparing surgery alone with (one cycle) chemoradiation followed by surgery is now underway.
Publisher: Oxford University Press (OUP)
Date: 26-10-2022
Abstract: We present early science results from Deep Investigation of Neutral Gas Origins (DINGO), an $\\rm H$i survey using the Australian Square Kilometre Array Pathfinder (ASKAP). Using ASKAP subarrays available during its commissioning phase, DINGO early science data were taken over ∼60 deg2 of the Galaxy And Mass Assembly (GAMA) 23 h region with 35.5 h integration time. We make direct detections of six known and one new sources at z & 0.01. Using $\\rm H$ i spectral stacking, we investigate the $\\rm H$ i gas content of galaxies at 0.04 & z & 0.09 for different galaxy colours. The results show that galaxy morphology based on optical colour is strongly linked to $\\rm H$ i gas properties. To examine environmental impacts on the $\\rm H$i gas content of galaxies, three subs les are made based on the GAMA group catalogue. The average $\\rm H$i mass of group central galaxies is larger than those of satellite and isolated galaxies, but with a lower $\\rm H$i gas fraction. We derive a variety of $\\rm H$i scaling relations for physical properties of our s le, including stellar mass, stellar mass surface density, NUV − r colour, specific star formation rate, and halo mass. We find that the derived $\\rm H$i scaling relations are comparable to other published results, with consistent trends also observed to ∼0.5 dex lower limits in stellar mass and stellar surface density. The cosmic $\\rm H$i densities derived from our data are consistent with other published values at similar redshifts. DINGO early science highlights the power of $\\rm H$i spectral stacking techniques with ASKAP.
Publisher: Oxford University Press (OUP)
Date: 09-2002
Publisher: Springer Science and Business Media LLC
Date: 07-2020
Publisher: American Astronomical Society
Date: 29-07-2013
Publisher: American Astronomical Society
Date: 20-05-2002
DOI: 10.1086/339843
Publisher: American Astronomical Society
Date: 03-2023
Abstract: We investigate shock structures driven by merger events in high-resolution simulations that result in a galaxy with a virial mass M ≈ 10 12 M ⊙ . We find that the sizes and morphologies of the internal shocks resemble remarkably well those of the newly detected class of odd radio circles (ORCs). This would highlight a so-far overlooked mechanism to form radio rings, shells, and even more complex structures around elliptical galaxies. Mach numbers of = 2–3 for such internal shocks are in agreement with the spectral indices of the observed ORCs. We estimate that ∼5% of galaxies could undergo merger events, which occasionally lead to such prominent structures within the galactic halo during their lifetime, explaining the low number of observed ORCs. At the time when the shock structures are matching the physical sizes of the observed ORCs, the central galaxies are typically classified as early-type galaxies, with no ongoing star formation, in agreement with observational findings. Although the energy released by such mergers could potentially power the observed radio luminosity already in Milky Way–like halos, our predicted luminosity from a simple, direct shock acceleration model is much smaller than the observed one. Considering the estimated number of candidates from our cosmological simulations and the higher observed energies, we suggest that the proposed scenario is more likely for halo masses around 10 13 M ⊙ in agreement with the observed stellar masses of the galaxies at the center of ORCs. Such shocks might be detectable with next-generation X-ray instruments like the Line Emission Mapper (LEM).
Publisher: Oxford University Press (OUP)
Date: 10-11-2016
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 08-2001
DOI: 10.1097/00008390-200108000-00014
Abstract: Isolated limb infusion (ILI) is an attractive, less complex alternative to isolated limb perfusion (ILP). It has a lower morbidity in treating localized recurrences and in transit metastases of the limb for tumours such as melanoma, Merkel cell tumour and Kaposi's sarcoma, allowing administration of high concentrations of cytotoxic agent to the affected limb under hypoxic conditions. Melphalan is the preferred cytotoxic agent for the treatment of melanoma by ILP or ILI. We report pharmacokinetic data from 12 patients treated by ILI for tumours of the limb in Brisbane. The kinetics of drug distribution in the limb was calculated using a two-compartment vascular model, where both tissue and infusate act as well-stirred compartments. Analysis of melphalan concentrations in the perfusate during ILI showed good agreement between the values measured and the concentrations predicted by the model. Recirculation and wash-out flow rates, tissue concentrations and the permeability surface area product (PS) were calculated. Correlations between the PS value and the drug concentrations in the perfusate and tissue were supported by the results. These data contribute to a better understanding of the distribution of melphalan during ILI in the limb, and offer the opportunity to optimize the drug regimen for patients undergoing ILI.
Publisher: Oxford University Press (OUP)
Date: 19-06-2015
Publisher: Oxford University Press (OUP)
Date: 05-07-2021
Abstract: We present sofia 2, the fully automated 3D source finding pipeline for the WALLABY extragalactic H i survey with the Australian SKA Pathfinder (ASKAP). sofia 2 is a reimplementation of parts of the original sofia pipeline in the c programming language and makes use of OpenMP for multithreading of the most time-critical algorithms. In addition, we have developed a parallel framework called sofia-X that allows the processing of large data cubes to be split across multiple computing nodes. As a result of these efforts, sofia 2 is substantially faster and comes with a much reduced memory footprint compared to its predecessor, thus allowing the large WALLABY data volumes of hundreds of gigabytes of imaging data per epoch to be processed in real time. The source code has been made publicly available to the entire community under an open-source licence. Performance tests using mock galaxies injected into genuine ASKAP data suggest that in the absence of significant imaging artefacts sofia 2 is capable of achieving near-100 per cent completeness and reliability above an integrated signal-to-noise ratio (SNR) of about 5–6. We also demonstrate that sofia 2 generally recovers the location, integrated flux, and w20 line width of galaxies with high accuracy. Other parameters, including the peak flux density and w50 line width, are more strongly biased due to the influence of the noise on the measurement. In addition, very faint galaxies below an integrated SNR of about 10 may get broken up into multiple components, thus requiring a strategy to identify fragmented sources and ensure that they do not affect the integrity of any scientific analysis based on the sofia 2 output.
Publisher: Oxford University Press (OUP)
Date: 09-2001
Publisher: American Astronomical Society
Date: 02-2002
DOI: 10.1086/338088
Publisher: Springer Science and Business Media LLC
Date: 08-1998
DOI: 10.1038/29466
Publisher: EDP Sciences
Date: 03-2020
DOI: 10.1051/0004-6361/201936556
Abstract: Context. This paper presents the analysis of optical integral field spectra for the H I eXtreme (H IX ) galaxy s le. H IX galaxies host at least 2.5 times more atomic gas (H I ) than expected from their optical R -band luminosity. Previous examination of their star formation activity and H I kinematics suggested that these galaxies stabilise their large H I discs (radii up to 94 kpc) against star formation due to their higher than average baryonic specific angular momentum. A comparison to semi-analytic models further showed that the elevated baryonic specific angular momentum is inherited from the high spin of the dark matter host. Aims. In this paper we now turn to the gas-phase metallicity as well as stellar and ionised gas kinematics in H IX galaxies to gain insights into recent accretion of metal-poor gas or recent mergers. Methods. We compare the stellar, ionised, and atomic gas kinematics, and examine the variation in the gas-phase metallicity throughout the stellar disc of H IX galaxies. Results. We find no indication for counter-rotation in any of the components, the central metallicities tend to be lower than average, but as low as expected for galaxies of similar H I mass. Metallicity gradients are comparable to other less H I -rich, local star forming galaxies. Conclusions. We conclude that H IX galaxies show no conclusive evidence for recent major accretion or merger events. Their overall lower metallicities are likely due to being hosted by high spin halos, which slows down their evolution and thus the enrichment of their interstellar medium.
Publisher: Oxford University Press (OUP)
Date: 05-09-2012
Publisher: American Astronomical Society
Date: 03-2004
DOI: 10.1086/381905
Publisher: MDPI AG
Date: 29-11-2018
Abstract: We present observations of linear polarisation in the southern radio lobe of Centaurus A, conducted during commissioning of the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. We used 16 antennas to observe a 30 square degree region in a single 12-h pointing over a 240 MHz band centred on 913 MHz. Our observations achieve an angular resolution of 26 × 33 arcseconds (480 parsecs), a maximum recoverable angular scale of 30 arcminutes, and a full-band sensitivity of 85 μ Jy beam − 1 . The resulting maps of polarisation and Faraday rotation are amongst the most detailed ever made for radio lobes, with order 10 5 resolution elements covering the source. We describe several as-yet unreported observational features of the lobe, including its detailed peak Faraday depth structure, and intricate networks of depolarised filaments. These results demonstrate the exciting capabilities of ASKAP for widefield radio polarimetry.
Publisher: Oxford University Press (OUP)
Date: 02-06-2021
Abstract: We report the discovery of large amounts of previously undetected cold neutral atomic hydrogen (H i) around the core triplet galaxies in the nearby NGC 7232 galaxy group with MeerKAT. With a physical resolution of ∼1 kpc, we detect a complex web of low-surface-brightness H i emission down to a 4σ column density level of ∼1 × 1019 cm−2 (over 44 km s−1). The newly discovered H i streams extend over ∼20 arcmin corresponding to 140 kpc in projection. This is approximately three times the H i extent of the galaxy triplet (52 kpc). The H i debris has an H i mass of ∼6.6 × 109 M⊙, more than 50 per cent of the total H i mass of the triplet. Within the galaxy triplet, NGC 7233 and NGC 7232 have lost a significant amount of H i while NGC 7232B appears to have an excess of H i. The H i deficiency in NGC 7232 and NGC 7233 indicates that galaxy–galaxy interaction in the group concentrates on this galaxy pair while the other disc galaxies have visited them over time. In comparison to the AMIGA s le of isolated galaxies, we find that with regards to its total H i mass the NGC 7232/3 galaxy triplet is not H i-deficient. Despite the many interactions associated to the triplet galaxies, no H i seems to have been lost from the group (yet).
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.3
Abstract: We describe the scientific goals and survey design of the First Large Absorption Survey in H i (FLASH), a wide field survey for 21-cm line absorption in neutral atomic hydrogen (H i ) at intermediate cosmological redshifts. FLASH will be carried out with the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope and is planned to cover the sky south of $\\delta \\approx +40\\,\\deg$ at frequencies between 711.5 and 999.5 MHz. At redshifts between $z = 0.4$ and $1.0$ (look-back times of 4 – 8 Gyr), the H i content of the Universe has been poorly explored due to the difficulty of carrying out radio surveys for faint 21-cm line emission and, at ultra-violet wavelengths, space-borne searches for D ed Lyman- $\\alpha$ absorption in quasar spectra. The ASKAP wide field of view and large spectral bandwidth, in combination with a radio-quiet site, will enable a search for absorption lines in the radio spectra of bright continuum sources over 80% of the sky. This survey is expected to detect at least several hundred intervening 21-cm absorbers and will produce an H i -absorption-selected catalogue of galaxies rich in cool, star-forming gas, some of which may be concealed from optical surveys. Likewise, at least several hundred associated 21-cm absorbers are expected to be detected within the host galaxies of radio sources at $0.4 z 1.0$ , providing valuable kinematical information for models of gas accretion and jet-driven feedback in radio-loud active galactic nuclei. FLASH will also detect OH 18-cm absorbers in diffuse molecular gas, megamaser OH emission, radio recombination lines, and stacked H i emission.
Publisher: Oxford University Press (OUP)
Date: 21-06-2000
Publisher: EDP Sciences
Date: 09-2023
Publisher: Cambridge University Press (CUP)
Date: 07-2014
DOI: 10.1017/S1743921314009272
Abstract: Here I present results from in idual galaxy studies and galaxy surveys in the Local Universe with particular emphasis on the spatially resolved properties of neutral hydrogen gas. The 3D nature of the data allows detailed studies of the galaxy morphology and kinematics, their relation to local and global star formation as well as galaxy environments. I use new 3D visualisation tools to present multi-wavelength data, aided by tilted-ring models of the warped galaxy disks. Many of the algorithms and tools currently under development are essential for the exploration of upcoming large survey data, but are also highly beneficial for the analysis of current galaxy surveys.
Publisher: American Astronomical Society
Date: 04-2006
DOI: 10.1086/500589
Publisher: American Astronomical Society
Date: 06-1997
DOI: 10.1086/304096
Publisher: Oxford University Press (OUP)
Date: 1999
DOI: 10.1143/PTPS.133.233
Publisher: American Astronomical Society
Date: 27-02-2013
Publisher: Oxford University Press (OUP)
Date: 07-06-2006
Publisher: EDP Sciences
Date: 26-02-2021
DOI: 10.1051/0004-6361/202039533
Abstract: The pre-merging system of galaxy clusters Abell 3391-Abell 3395 located at a mean redshift of 0.053 has been observed at 1 GHz in an ASKAP/EMU Early Science observation as well as in X-rays with eROSITA. The projected separation of the X-ray peaks of the two clusters is ~50′ or ~3.1 Mpc. Here we present an inventory of interesting radio sources in this field around this cluster merger. While the eROSITA observations provide clear indications of a bridge of thermal gas between the clusters, neither ASKAP nor MWA observations show any diffuse radio emission coinciding with the X-ray bridge. We derive an upper limit on the radio emissivity in the bridge region of 〈 J 〉 1 GHz 1.2 × 10 −44 W Hz −1 m −3 . A non-detection of diffuse radio emission in the X-ray bridge between these two clusters has implications for particle-acceleration mechanisms in cosmological large-scale structure. We also report extended or otherwise noteworthy radio sources in the 30 deg 2 field around Abell 3391-Abell 3395. We identified 20 Giant Radio Galaxies, plus 7 candidates, with linear projected sizes greater than 1 Mpc. The sky density of field radio galaxies with largest linear sizes of .7 Mpc is ≈1.7 deg −2 , three times higher than previously reported. We find no evidence for a cosmological evolution of the population of Giant Radio Galaxies. Moreover, we find seven candidates for cluster radio relics and radio halos.
Publisher: EDP Sciences
Date: 27-01-2017
Publisher: American Astronomical Society
Date: 03-1995
DOI: 10.1086/175397
Publisher: EDP Sciences
Date: 27-02-2012
Publisher: Oxford University Press (OUP)
Date: 21-07-2008
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2021.44
Abstract: The Variables and Slow Transients Survey (VAST) on the Australian Square Kilometre Array Pathfinder (ASKAP) is designed to detect highly variable and transient radio sources on timescales from 5 s to $\\sim\\!5$ yr. In this paper, we present the survey description, observation strategy and initial results from the VAST Phase I Pilot Survey. This pilot survey consists of $\\sim\\!162$ h of observations conducted at a central frequency of 888 MHz between 2019 August and 2020 August, with a typical rms sensitivity of $0.24\\ \\mathrm{mJy\\ beam}^{-1}$ and angular resolution of $12-20$ arcseconds. There are 113 fields, each of which was observed for 12 min integration time, with between 5 and 13 repeats, with cadences between 1 day and 8 months. The total area of the pilot survey footprint is 5 131 square degrees, covering six distinct regions of the sky. An initial search of two of these regions, totalling 1 646 square degrees, revealed 28 highly variable and/or transient sources. Seven of these are known pulsars, including the millisecond pulsar J2039–5617. Another seven are stars, four of which have no previously reported radio detection (SCR J0533–4257, LEHPM 2-783, UCAC3 89–412162 and 2MASS J22414436–6119311). Of the remaining 14 sources, two are active galactic nuclei, six are associated with galaxies and the other six have no multi-wavelength counterparts and are yet to be identified.
Publisher: Oxford University Press (OUP)
Date: 09-2023
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2021.42
Abstract: We present the data and initial results from the first pilot survey of the Evolutionary Map of the Universe (EMU), observed at 944 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The survey covers $270 \\,\\mathrm{deg}^2$ of an area covered by the Dark Energy Survey, reaching a depth of 25–30 $\\mu\\mathrm{Jy\\ beam}^{-1}$ rms at a spatial resolution of $\\sim$ 11–18 arcsec, resulting in a catalogue of $\\sim$ 220 000 sources, of which $\\sim$ 180 000 are single-component sources. Here we present the catalogue of single-component sources, together with (where available) optical and infrared cross-identifications, classifications, and redshifts. This survey explores a new region of parameter space compared to previous surveys. Specifically, the EMU Pilot Survey has a high density of sources, and also a high sensitivity to low surface brightness emission. These properties result in the detection of types of sources that were rarely seen in or absent from previous surveys. We present some of these new results here.
Publisher: Cambridge University Press (CUP)
Date: 08-2012
DOI: 10.1017/S1743921312021606
Abstract: The 2mass Tully–Fisher Survey (2 mtf ) aims to measure Tully–Fisher (TF) distances for all bright, inclined spirals in the 2mass Redshift Survey (2 mrs ) using high-quality H i widths and 2mass photometry. Compared with previous peculiar-velocity surveys, the 2 mtf survey provides more accurate width measurements and more uniform sky coverage, combining observations with the Green Bank, Arecibo , and Parkes telescopes. With this new redshift-independent distance database, we will significantly improve our understanding of the mass distribution in the local Universe.
Publisher: Oxford University Press (OUP)
Date: 05-01-2019
DOI: 10.1093/MNRAS/STZ017
Abstract: We report on neutral hydrogen (H i) observations of the NGC 7232 group with the Australian Square Kilometre Array Pathfinder (ASKAP). These observations were conducted as part of the Wide-field ASKAP L-Band Legacy All-sky Blind surveY (WALLABY) Early Science program with an array of 12 ASKAP antennas equipped with Phased Array Feeds, which were used to form 36 beams to map a field of view of 30 deg2. Analysing a subregion of the central beams, we detect 17 H i sources. Eleven of these detections are identified as galaxies and have stellar counterparts, of which five are newly resolved H i galaxy sources. The other six detections appear to be tidal debris in the form of H i clouds that are associated with the central triplet, NGC 7232/3, comprising the spiral galaxies NGC 7232, NGC 7232B, and NGC 7233. One of these H i clouds has a mass of MH i ∼ 3 × 108 M⊙ and could be the progenitor of a long-lived tidal dwarf galaxy. The remaining H i clouds are likely transient tidal knots that are possibly part of a diffuse tidal bridge between NGC 7232/3 and another group member, the lenticular galaxy IC 5181.
Start Date: 07-2003
End Date: 06-2006
Amount: $193,035.00
Funder: Australian Research Council
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End Date: 12-2024
Amount: $510,000.00
Funder: Australian Research Council
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End Date: 10-2014
Amount: $835,200.00
Funder: Australian Research Council
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End Date: 05-2015
Amount: $556,800.00
Funder: Australian Research Council
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End Date: 06-2027
Amount: $1,275,295.00
Funder: Australian Research Council
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End Date: 08-2016
Amount: $350,000.00
Funder: Australian Research Council
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End Date: 12-2024
Amount: $30,300,000.00
Funder: Australian Research Council
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