ORCID Profile
0000-0002-8057-0294
Current Organisation
University of Western Australia
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Astronomical and Space Sciences | Astronomical and Space Instrumentation | Cosmology and Extragalactic Astronomy | Galactic Astronomy | Astronomy And Astrophysics | Signal Processing | Space and Solar Physics | Ionospheric And Magnetospheric Physics | Stellar Astronomy and Planetary Systems | General Relativity and Gravitational Waves
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Publisher: Oxford University Press (OUP)
Date: 21-03-2003
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: EDP Sciences
Date: 10-2016
Publisher: American Astronomical Society
Date: 06-2000
DOI: 10.1086/301374
Publisher: American Astronomical Society
Date: 09-2008
DOI: 10.1086/590330
Publisher: Oxford University Press (OUP)
Date: 09-10-2017
Publisher: Oxford University Press (OUP)
Date: 21-06-2017
Publisher: Oxford University Press (OUP)
Date: 20-02-2019
Publisher: Springer Science and Business Media LLC
Date: 21-03-2019
Publisher: American Astronomical Society
Date: 12-07-2005
DOI: 10.1086/432836
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: American Astronomical Society
Date: 02-2023
Abstract: We use the single-dish radio telescope Five-hundred meter Aperture Spherical Telescope (FAST) to map the H i in the tidally interacting NGC 4631 group with a resolution of 3.′24 (7 kpc), reaching a 5 σ column density limit of 10 17.9 cm −2 assuming a line width of 20 km s −1 . Taking the existing interferometric H i image from the Hydrogen Accretion in LOcal GAlaxieS project of Westerbork Synthesis Radio Telescope as a reference, we are able to identify and characterize a significant excess of large-scale, low-density, and diffuse H i in the group. This diffuse H i extends more than 120 kpc across, and accounts for more than one-fourth of the total H i detected by FAST in and around the galaxy NGC 4631. In the region of the tidal tails, the diffuse H i has a typical column density above 10 19.5 cm −2 , and is highly turbulent with a velocity dispersion of around 50 km s −1 . It increases in column density with the dense H i , and tends to be associated with the kinematically hotter part of the dense H i . Through simple modeling, we find that the majority of the diffuse H i in the tail region is likely to induce cooling out of the hot intragalactic medium (IGM) instead of evaporating or being radiatively ionized. Given these relations of gas in different phases, the diffuse H i may represent a condensing phase of the IGM. Ongoing and past active tidal interactions may have produced the wide-spreading H i distribution, and triggered the gas accretion to NGC 4631 through the phase of the diffuse H i .
Publisher: Oxford University Press (OUP)
Date: 11-04-2001
Publisher: American Astronomical Society
Date: 06-10-2006
DOI: 10.1086/508227
Publisher: Oxford University Press (OUP)
Date: 21-11-2005
Publisher: Springer Netherlands
Date: 2007
Publisher: American Astronomical Society
Date: 09-10-2009
Publisher: Oxford University Press (OUP)
Date: 02-2013
DOI: 10.1093/MNRAS/STT002
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: American Astronomical Society
Date: 08-10-2009
Publisher: Oxford University Press (OUP)
Date: 04-2010
Publisher: Oxford University Press (OUP)
Date: 2003
Publisher: American Astronomical Society
Date: 20-08-1998
DOI: 10.1086/306010
Publisher: American Astronomical Society
Date: 12-1991
DOI: 10.1086/170806
Publisher: Cambridge University Press (CUP)
Date: 2019
DOI: 10.1017/PASA.2019.37
Abstract: This work makes available a further $2\,860~\text{deg}^2$ of the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey, covering half of the accessible galactic plane, across 20 frequency bands s ling 72–231 MHz, with resolution $4\,\text{arcmin}-2\,\text{arcmin}$ . Unlike previous GLEAM data releases, we used multi-scale CLEAN to better deconvolve large-scale galactic structure. For the galactic longitude ranges $345^\circ l 67^\circ$ , $180^\circ l 240^\circ$ , we provide a compact source catalogue of 22 037 components selected from a 60-MHz bandwidth image centred at 200 MHz, with RMS noise $\approx10-20\,\text{mJy}\,\text{beam}^{-1}$ and position accuracy better than 2 arcsec. The catalogue has a completeness of 50% at ${\approx}120\,\text{mJy}$ , and a reliability of 99.86%. It covers galactic latitudes $1^\circ\leq|b|\leq10^\circ$ towards the galactic centre and $|b|\leq10^\circ$ for other regions, and is available from Vizier images covering $|b|\leq10^\circ$ for all longitudes are made available on the GLEAM Virtual Observatory (VO).server and SkyView.
Publisher: Cambridge University Press (CUP)
Date: 04-1995
DOI: 10.1017/S1323358000019986
Abstract: This paper describes the first results from a 20 deg 2 mosaic of the Small Magellanic Cloud (SMC) in the λ 21-cm line of neutral hydrogen. The mosaic consists of 320 separate pointings with the 375-m array of the Australia Telescope Compact Array. The angular resolution is 1′· 5 (26 pc, for a distance of 60 kpc) and the velocity resolution is l·6kms −1 . The images reveal a structure of remarkable complexity, with much of the spatial power contained in high-brightness temperature compact knots and filaments. Numerous wind-blown ‘bubbles’ and ‘supershells’ are evident in the data, both inside and outside the stellar confines of the SMC. Some high-density H I regions are seen to correlate with H α regions, indicating sites of current star formation. However, many high-column-density H I regions are devoid of optical emission and may represent regions of future star formation. These regions may be under-abundant in diffuse molecular gas due to the high radiation field and low metallicity of the SMC.
Publisher: American Astronomical Society
Date: 17-01-2012
Publisher: Cambridge University Press (CUP)
Date: 2019
DOI: 10.1017/PASA.2019.33
Abstract: We examined the latest data release from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey covering 345° l 60° and 180° l 240°, using these data and that of the Widefield Infrared Survey Explorer to follow up proposed candidate Supernova Remnant (SNR) from other sources. Of the 101 candidates proposed in the region, we are able to definitively confirm ten as SNRs, tentatively confirm two as SNRs, and reclassify five as H ii regions. A further two are detectable in our images but difficult to classify the remaining 82 are undetectable in these data. We also investigated the 18 unclassified Multi-Array Galactic Plane Imaging Survey (MAGPIS) candidate SNRs, newly confirming three as SNRs, reclassifying two as H ii regions, and exploring the unusual spectra and morphology of two others.
Publisher: Cambridge University Press (CUP)
Date: 2019
DOI: 10.1017/PASA.2019.34
Abstract: We have detected 27 new supernova remnants (SNRs) using a new data release of the GLEAM survey from the Murchison Widefield Array telescope, including the lowest surface brightness SNR ever detected, G 0.1 – 9.7. Our method uses spectral fitting to the radio continuum to derive spectral indices for 26/27 candidates, and our low-frequency observations probe a steeper spectrum population than previously discovered. None of the candidates have coincident WISE mid-IR emission, further showing that the emission is non-thermal. Using pulsar associations we derive physical properties for six candidate SNRs, finding G 0.1 – 9.7 may be younger than 10 kyr. Sixty per cent of the candidates subtend areas larger than 0.2 deg 2 on the sky, compared to 25% of previously detected SNRs. We also make the first detection of two SNRs in the Galactic longitude range 220°–240°.
Publisher: EDP Sciences
Date: 27-07-2015
Publisher: American Astronomical Society
Date: 14-07-2020
Publisher: Oxford University Press (OUP)
Date: 13-08-2015
Publisher: American Astronomical Society
Date: 08-2012
Publisher: Cambridge University Press (CUP)
Date: 1999
DOI: 10.1071/AS99008
Abstract: The H I Parkes All Sky Survey (HIPASS) is a blind search for extragalactic neutral hydrogen, covering the whole of the southern sky. We present the latest H I mass function (HIMF) constructed from a s le of 263 galaxies with declinations −62°. Standard Σ1/ V max and maximum likelihood techniques are used in the analysis. No upturn in the low-mass end of the HIMF is yet seen, though our selection procedure presently conspires against the lowest-mass galaxies.
Publisher: Oxford University Press (OUP)
Date: 14-08-2017
Publisher: American Astronomical Society
Date: 11-1990
DOI: 10.1086/169383
Publisher: American Astronomical Society
Date: 09-08-2018
Publisher: Oxford University Press (OUP)
Date: 17-03-2020
Abstract: The search for emission from weakly interacting massive particle (WIMP) dark matter annihilation and decay has become a multipronged area of research not only targeting a erse selection of astrophysical objects, but also taking advantage of the entire electromagnetic spectrum. The decay of WIMP particles into standard model particles has been suggested as a possible channel for synchrotron emission to be detected at low radio frequencies. Here, we present the stacking analysis of a s le of 33 dwarf spheroidal (dSph) galaxies with low-frequency (72–231 MHz) radio images from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. We produce radial surface brightness profiles of images centred upon each dSph galaxy with background radio sources masked. We remove 10 fields from the stacking due to contamination from either poorly subtracted, bright radio sources or strong background gradients across the field. The remaining 23 dSph galaxies are stacked in an attempt to obtain a statistical detection of any WIMP-induced synchrotron emission in these systems. We find that the stacked radial brightness profile does not exhibit a statistically significant detection above the 95 per cent confidence level of ∼1.5 mJy beam−1. This novel technique shows the potential of using low-frequency radio images to constrain fundamental properties of particle dark matter.
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: Springer Netherlands
Date: 2008
Publisher: Oxford University Press (OUP)
Date: 14-06-2018
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.10
Abstract: The entire southern sky (Declination, $\delta 30^{\circ}$ ) has been observed using the Murchison Widefield Array (MWA), which provides radio imaging of $\sim$ 2 arcmin resolution at low frequencies (72–231 MHz). This is the GaLactic and Extragalactic All-sky MWA (GLEAM) Survey, and we have previously used a combination of visual inspection, cross-checks against the literature, and internal matching to identify the ‘brightest’ radio-sources ( $S_{\mathrm{151\,MHz}} $ Jy) in the extragalactic catalogue (Galactic latitude, $|b| ^{\circ}$ ). We refer to these 1 863 sources as the GLEAM 4-Jy (G4Jy) S le, and use radio images (of ${\leq}45$ arcsec resolution), and multi-wavelength information, to assess their morphology and identify the galaxy that is hosting the radio emission (where appropriate). Details of how to access all of the overlays used for this work are available at vw26/G4Jy . Alongside this we conduct further checks against the literature, which we document here for in idual sources. Whilst the vast majority of the G4Jy S le are active galactic nuclei with powerful radio-jets, we highlight that it also contains a nebula, two nearby, star-forming galaxies, a cluster relic, and a cluster halo. There are also three extended sources for which we are unable to infer the mechanism that gives rise to the low-frequency emission. In the G4Jy catalogue we provide mid-infrared identifications for 86% of the sources, and flag the remainder as: having an uncertain identification (129 sources), having a faint/uncharacterised mid-infrared host (126 sources), or it being inappropriate to specify a host (2 sources). For the subset of 129 sources, there is ambiguity concerning candidate host-galaxies, and this includes four sources (B0424–728, B0703–451, 3C 198, and 3C 403.1) where we question the existing identification.
Publisher: Oxford University Press (OUP)
Date: 06-06-2013
DOI: 10.1093/MNRAS/STT810
Publisher: American Astronomical Society
Date: 2002
DOI: 10.1086/338092
Publisher: American Astronomical Society
Date: 04-1995
DOI: 10.1086/117388
Publisher: American Astronomical Society
Date: 12-1999
DOI: 10.1086/301116
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: Springer Netherlands
Date: 2008
Publisher: Springer Science and Business Media LLC
Date: 2013
DOI: 10.1038/NATURE11734
Abstract: The nucleus of the Milky Way is known to harbour regions of intense star formation activity as well as a supermassive black hole. Recent observations have revealed regions of γ-ray emission reaching far above and below the Galactic Centre (relative to the Galactic plane), the so-called 'Fermi bubbles'. It is uncertain whether these were generated by nuclear star formation or by quasar-like outbursts of the central black hole and no information on the structures' magnetic field has been reported. Here we report observations of two giant, linearly polarized radio lobes, containing three ridge-like substructures, emanating from the Galactic Centre. The lobes each extend about 60 degrees in the Galactic bulge, closely corresponding to the Fermi bubbles, and are permeated by strong magnetic fields of up to 15 microgauss. We conclude that the radio lobes originate in a biconical, star-formation-driven (rather than black-hole-driven) outflow from the Galaxy's central 200 parsecs that transports a huge amount of magnetic energy, about 10(55) ergs, into the Galactic halo. The ridges wind around this outflow and, we suggest, constitute a 'phonographic' record of nuclear star formation activity over at least ten million years.
Publisher: American Astronomical Society
Date: 05-2023
Publisher: Oxford University Press (OUP)
Date: 2019
DOI: 10.1093/MNRAS/STZ565
Publisher: American Astronomical Society
Date: 04-2022
Abstract: We perform a profile analysis of the combined H i data cube of the Large Magellanic Cloud (LMC) from observations with the Australia Telescope Compact Array and the Parkes radio telescope. For the profile analysis, we use a newly developed algorithm that decomposes in idual line profiles into an optimal number of Gaussian components based on a Bayesian nested s ling. The decomposed Gaussian components are then classified into kinematically cold, warm, and hot gas components based on their velocity dispersion. The estimated masses of the kinematically cold, warm, and hot gas components are ∼12.2%, ∼58.3%, and ∼29.5% of the total H i mass of the LMC, respectively. Our analysis reveals the highly complex H i structure and kinematics of the LMC that are seen in previous studies but in a more quantitative manner. We also extract the undisturbed H i gas bulk motions and derive new H i gas bulk rotation curves of the LMC by applying a 2D tilted-ring analysis. In contrast to previously derived H i rotation curves, the newly derived bulk rotation curves are much more consistent with the carbon star kinematics, with rotation velocity linearly increasing in the inner part and reaching a maximum of ∼60 km s −1 at the outermost measured radius. By comparing the lower bulk rotation curves with previous studies, we conclude that there is a lower dynamical contribution of dark matter in the central part of the LMC.
Publisher: American Astronomical Society
Date: 09-02-2015
Publisher: EDP Sciences
Date: 12-1996
DOI: 10.1051/AAS:1996287
Publisher: Oxford University Press (OUP)
Date: 06-2004
Publisher: Cambridge University Press (CUP)
Date: 1993
DOI: 10.1017/S1323358000025972
Abstract: The radio emission associated with SN 1987A appears to be synchrotron emission resulting from the acceleration of electrons at the interface between the outward moving shock wave and clumps of circumstellar material. The Australia Telescope Compact Array is now able to resolve this region, which has dimensions of ~ arcsec, revealing a slight (10%) asphericity in the distribution of the low density gas within the [OIII] circumstellar ring. Assuming that the radio emission arises from a region just behind the shock front, we deduce a mean radial expansion velocity, from 1987 to 1992, of 29 200 kms. First observed contact of the shock with the [OIII] circumstellar ring could occur as early as mid-1993, depending on the deceleration in the intervening gas. This will probably be closely followed by shock-excited optical lines, a strong X-ray outburst and a further increase in the radio emission.
Publisher: American Astronomical Society
Date: 30-12-2010
Publisher: Springer Science and Business Media LLC
Date: 10-1990
DOI: 10.1038/347650A0
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: 02-10-2021
Abstract: We use the 21-cm emission-line data from the Deep Investigation of Neutral Gas Origin-Very Large Array (DINGO-VLA) project to study the atomic hydrogen gas H i of the Universe at redshifts z & 0.1. Results are obtained using a stacking analysis, combining the H i signals from 3622 galaxies extracted from 267 VLA pointings in the G09 field of the Galaxy and Mass Assembly Survey (GAMA). Rather than using a traditional one-dimensional spectral stacking method, a three-dimensional cubelet stacking method is used to enable deconvolution and the accurate recovery of average galaxy fluxes from this high-resolution interferometric data set. By probing down to galactic scales, this experiment also overcomes confusion corrections that have been necessary to include in previous single-dish studies. After stacking and deconvolution, we obtain a 30σ H i mass measurement from the stacked spectrum, indicating an average H i mass of ${\\rm{M_{\\rm{{H}\\,\\small{I}}}}}=(1.67\\pm 0.18)\\times 10^{9}~{\\rm{{\\rm M}_{\\odot }}}$. The corresponding cosmic density of neutral atomic hydrogen is ${\\rm{\\Omega _{\\rm{{H}\\,\\small{I}}}}}=(0.38\\pm 0.04)\\times 10^{-3}$ at redshift of z = 0.051. These values are in good agreement with earlier results, implying there is no significant evolution of $\\Omega _{\\rm{{H}\\,\\small{I}}}$ at lower redshifts.
Publisher: IOP Publishing
Date: 11-2002
DOI: 10.1086/343220
Publisher: Oxford University Press (OUP)
Date: 22-02-2018
DOI: 10.1093/MNRAS/STY479
Publisher: EDP Sciences
Date: 22-02-2005
Publisher: Oxford University Press (OUP)
Date: 12-2007
Publisher: American Astronomical Society
Date: 06-11-2019
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: 19-01-2017
DOI: 10.1093/MNRAS/STX155
Publisher: Oxford University Press (OUP)
Date: 17-04-2013
DOI: 10.1093/MNRAS/STT471
Publisher: Oxford University Press (OUP)
Date: 11-1998
Publisher: Oxford University Press (OUP)
Date: 06-2004
Publisher: Oxford University Press (OUP)
Date: 18-10-2012
Publisher: Springer Netherlands
Date: 2007
Publisher: Oxford University Press (OUP)
Date: 06-09-2017
Publisher: American Astronomical Society
Date: 20-12-2000
DOI: 10.1086/317865
Publisher: American Astronomical Society
Date: 12-2008
DOI: 10.1086/590546
Publisher: Oxford University Press (OUP)
Date: 23-01-2021
Abstract: In this paper, we introduce a method for stacking data cubelets extracted from interferometric surveys of galaxies in the redshifted 21-cm H},i line. Unlike the traditional spectral stacking technique, which stacks one-dimensional spectra extracted from data cubes, we examine a method based on image domain stacks that makes deconvolution possible. To test the validity of this assumption, we mock a s le of 3622 equatorial galaxies extracted from the GAMA survey, recently imaged as part of a DINGO-VLA project. We first examine the accuracy of the method using a noise-free simulation and note that the stacked image and flux estimation are dramatically improved compared to traditional stacking. The extracted H i mass from the deconvolved image agrees with the average input mass to within 3 per cent. However, with traditional spectral stacking, the derived H i is incorrect by greater than a factor of 2. For a more realistic case of a stack with finite S/N, we also produced 20 different noise realizations to closely mimic the properties of the DINGO-VLA interferometric survey. We recovered the predicted average H i mass to within ∼4 per cent. Compared with traditional spectral stacking, this technique extends the range of science applications where stacking can be used, and is especially useful for characterizing the emission from extended sources with interferometers.
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: 26-11-2016
Publisher: American Astronomical Society
Date: 10-01-2007
DOI: 10.1086/508799
Publisher: American Astronomical Society
Date: 13-04-2010
Publisher: Oxford University Press (OUP)
Date: 14-04-2018
DOI: 10.1093/MNRAS/STY928
Publisher: Oxford University Press (OUP)
Date: 2005
Publisher: American Astronomical Society
Date: 05-1997
DOI: 10.1086/118377
Publisher: Oxford University Press (OUP)
Date: 05-04-2017
DOI: 10.1093/MNRAS/STX830
Publisher: American Astronomical Society
Date: 06-1998
DOI: 10.1086/300367
Publisher: American Astronomical Society
Date: 29-11-2011
Publisher: Oxford University Press (OUP)
Date: 21-07-2017
Publisher: Oxford University Press (OUP)
Date: 08-06-2016
Publisher: American Astronomical Society
Date: 03-1990
DOI: 10.1086/185673
Publisher: Oxford University Press (OUP)
Date: 10-06-2019
Abstract: Measurements of the growth rate of structure, fσ8, in the low-redshift Universe allow stringent tests of the cosmological model. In this work, we provide new constraints on fσ8 at an effective redshift of z = 0.03 using the combined density and velocity fields measured by the 2MTF and 6dFGSv surveys. We do this by applying a new estimator of the redshift-space density and momentum (density-weighted velocity) power spectra, developed in the first paper of this series, to measured redshifts and peculiar velocities from these data sets. We combine this with models of the density and momentum power spectra in the presence of complex survey geometries and with an ensemble of simulated galaxy catalogues that match the survey selection functions and galaxy bias. We use these simulations to estimate the errors on our measurements and identify possible systematics. In particular, we are able to identify and remove biases caused by the non-Gaussianity of the power spectra by applying the Box-Cox transformation to the power spectra prior to fitting. After thorough validation of our methods we recover a constraint of $f\\sigma _8(z_{\\mathrm{eff}}=0.03)=0.404^{+0.082}_{-0.081}$ from the combined 2MTF and 6dFGSv data. This measurement is fully consistent with the expectations of general relativity and the Λ cold dark matter cosmological model. It is also comparable and complementary to constraints using different techniques on similar data, affirming the usefulness of our method for extracting cosmology from velocity fields.
Publisher: Oxford University Press (OUP)
Date: 22-10-2020
Abstract: The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has started the Commensal Radio Astronomy FasT Survey (CRAFTS). In this paper, we use the technical parameters of FAST derived from commissioning observations to simulate the completeness function for extragalactic H i survey of CRAFTS, H i galaxies from two kinds of mock catalogues are selected. One is generated by Monte Carlo simulation based on the interpolated mass–velocity width function of the ALFALFA $100{{\\ \\rm per\\ cent}}$ (a.k.a. α.100) catalogue. The other is constructed by semi-analytical N-body simulation based on the ΛCDM model. Our results suggest that a two-pass CRAFTS extragalactic H i survey will be able to detect nearly 4.8 × 105 galaxies, from which the ‘faint end’ slope of the H i mass function (HIMF) can be recovered to $\\mathrm{10^{7}\\, M_{\\odot }}$ and the ‘knee mass’ of the HIMF can be measured to a redshift of 0.1. Considering the radio frequency interference status and sensitivity limitation, CRAFTS will be efficient in detecting H i galaxies at redshifts below 0.1, which implies a tremendous potential in exploring the galaxy interactions in different environments and the spatial distribution of H i galaxies in the local universe.
Publisher: Cambridge University Press (CUP)
Date: 2017
DOI: 10.1017/PASA.2017.45
Abstract: We present first results from pilot observations using a phased array feed (PAF) mounted on the Parkes 64-m radio telescope. The observations presented here cover a frequency range from 1 150 to 1 480 MHz and are used to show the ability of PAFs to suppress standing wave problems by a factor of ~10, which afflict normal feeds. We also compare our results with previous HIPASS observations and with previous H i images of the Large Magellanic Cloud. Drift scan observations of the GAMA G23 field resulted in direct H i detections at z = 0.0043 and z = 0.0055 of HIPASS galaxies J2242-30 and J2309-30. Our new measurements generally agree with archival data in spectral shape and flux density, with small differences being due to differing beam patterns. We also detect signal in the stacked H i data of 1 094 in idually undetected galaxies in the GAMA G23 field in the redshift range 0.05 ⩽ z ⩽ 0.075. Finally, we use the low standing wave ripple and wide bandwidth of the PAF to set a 3σ upper limit to any positronium recombination line emission from the Galactic Centre of .09 K, corresponding to a recombination rate of .0 × 10 45 s −1 .
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: 12-2004
DOI: 10.1086/425154
Publisher: American Astronomical Society
Date: 07-2001
DOI: 10.1086/321453
Publisher: Springer Science and Business Media LLC
Date: 31-07-2008
Publisher: American Astronomical Society
Date: 24-04-2015
Publisher: American Astronomical Society
Date: 07-10-2014
Publisher: Oxford University Press (OUP)
Date: 28-12-2015
Publisher: American Astronomical Society
Date: 20-06-2013
Publisher: American Astronomical Society
Date: 20-02-2001
DOI: 10.1086/319021
Publisher: American Astronomical Society
Date: 03-12-2014
Publisher: American Astronomical Society
Date: 07-1993
DOI: 10.1086/172877
Publisher: Oxford University Press (OUP)
Date: 28-08-2021
Abstract: We apply a spectral stacking technique to Westerbork Synthesis Radio Telescope observations to measure the neutral atomic hydrogen content (H i) of nearby galaxies in and around galaxy groups at z & 0.11. Our s le includes 577 optically selected galaxies (120 isolated galaxies and 457 satellites) covering stellar masses between 1010 and 1011.5 M⊙, cross-matched with Yang’s group catalogue, with angular and redshift positions from the Sloan Digital Sky Survey. We find that the satellites in the centres of groups have lower H i masses at fixed stellar mass and morphology (characterized by the inverse concentration index) relative to those at larger radii. These trends persist for satellites in both high-mass ($M_{\\rm halo} \\gt 10^{13.5}\\, h^{-1}\\, \\mathrm{M}_{\\odot }$) and low-mass ($M_{\\rm halo} \\leqslant 10^{13.5}\\, h^{-1}\\, \\mathrm{M}_{\\odot }$) groups, but disappear if we only consider group members in low local density (Σ & 5 gal Mpc−2) environments. Similar trends are found for the specific star formation rate. Interestingly, we find that the radial trends of decreasing H i mass with decreasing group-centric radius extend beyond the group virial radius, as isolated galaxies close to larger groups lack H i compared with those located more than ∼3.0 R180 away from the centre of their nearest group. We also measure these trends in the late-type subs le and obtain similar results. Our results suggest that the H i reservoir of galaxies can be affected before galaxies become group satellites, indicating the existence of pre-processing in the infalling isolated galaxies.
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: Oxford University Press (OUP)
Date: 06-1996
Publisher: IOP Publishing
Date: 11-1979
Publisher: Oxford University Press (OUP)
Date: 21-01-1999
Publisher: Oxford University Press (OUP)
Date: 10-2002
Publisher: Springer Science and Business Media LLC
Date: 07-2020
Publisher: Oxford University Press (OUP)
Date: 28-09-2017
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: Cambridge University Press (CUP)
Date: 02-2017
DOI: 10.1017/S1743921317004719
Abstract: Supernova (SN) 1987A has provided a unique opportunity to study how SN ejecta evolve in 30 years time scale. We report our ALMA spectral observations of SN 1987A, taken in 2014, 2015 and 2016, with detections of CO, 28 SiO, HCO + and SO, with weaker lines of 29 SiO. We find a dip in the SiO line profiles, suggesting that the ejecta morphology is likely elongated. The difference of the CO and SiO line profiles is consistent with hydrodynamic simulations, which show that Rayleigh-Taylor instabilities causes mixing of gas, with heavier elements much more disturbed, making more elongated structure. Using 28 SiO and its isotopologues, Si isotope ratios were estimated for the first time in SN 1987A. The estimated ratios appear to be consistent with theoretical predictions of inefficient formation of neutron rich atoms at lower metallicity, such as observed in the Large Magellanic Cloud (about half a solar metallicity). The deduced large HCO + mass and small SiS mass, which are inconsistent to the predictions of chemical model, might be explained by some mixing of elements immediately after the explosion. The mixing might have made some hydrogen from the envelope to sink into carbon and oxygen-rich zone during early days after the explosion, enabling the formation of a substantial mass of HCO + . Oxygen atoms may penetrate into silicon and sulphur zone, suppressing formation of SiS. Our ALMA observations open up a new window to investigate chemistry, dynamics and explosive-nucleosynthesis in supernovae.
Publisher: Cambridge University Press (CUP)
Date: 2017
DOI: 10.1017/PASA.2017.54
Abstract: The Murchison Widefield Array (MWA), located in Western Australia, is one of the low-frequency precursors of the international Square Kilometre Array (SKA) project. In addition to pursuing its own ambitious science programme, it is also a testbed for wide range of future SKA activities ranging from hardware, software to data analysis. The key science programmes for the MWA and SKA require very high dynamic ranges, which challenges calibration and imaging systems. Correct calibration of the instrument and accurate measurements of source flux densities and polarisations require precise characterisation of the telescope’s primary beam. Recent results from the MWA GaLactic Extragalactic All-sky Murchison Widefield Array (GLEAM) survey show that the previously implemented Average Embedded Element (AEE) model still leaves residual polarisations errors of up to 10–20% in Stokes Q. We present a new simulation-based Full Embedded Element (FEE) model which is the most rigorous realisation yet of the MWA’s primary beam model. It enables efficient calculation of the MWA beam response in arbitrary directions without necessity of spatial interpolation. In the new model, every dipole in the MWA tile (4 × 4 bow-tie dipoles) is simulated separately, taking into account all mutual coupling, ground screen, and soil effects, and therefore accounts for the different properties of the in idual dipoles within a tile. We have applied the FEE beam model to GLEAM observations at 200–231 MHz and used false Stokes parameter leakage as a metric to compare the models. We have determined that the FEE model reduced the magnitude and declination-dependent behaviour of false polarisation in Stokes Q and V while retaining low levels of false polarisation in Stokes U.
Publisher: Oxford University Press (OUP)
Date: 07-06-2010
Publisher: American Astronomical Society
Date: 20-01-2007
DOI: 10.1086/509104
Publisher: Oxford University Press (OUP)
Date: 12-06-2018
Publisher: Oxford University Press (OUP)
Date: 06-1987
Publisher: Cambridge University Press (CUP)
Date: 2002
DOI: 10.1071/AS01042
Abstract: The development of the radio remnant of SN 1987A has been followed using the Australia Telescope Compact Array since its first detection in 1990 August. The remnant has been observed at four frequencies, 1.4, 2.4, 4.8, and 8.6 GHz, at intervals of 4–6 weeks since the first detection. These data are combined with the 843 MHz data set of Ball et al. (2001) obtained at Molonglo Observatory to study the spectral and temporal variations of the emission. These observations show that the remnant continues to increase in brightness, with a larger rate of increase at recent times. They also show that the radio spectrum is becoming flatter, with the spectral index changing from −0.97 to −0.88 over the 11 years. In addition, at roughly yearly intervals since 1992, the remnant has been imaged at 9 GHz using super-resolution techniques to obtain an effective synthesised beamwidth of about 0″.5. The imaging observations confirm the shell morphology of the radio remnant and show that it continues to expand at ˜3000 km s −1 . The bright regions of radio emission seen on the limb of the shell do not appear to be related to the optical hot spots which have subsequently appeared in surrounding circumstellar material.
Publisher: Oxford University Press (OUP)
Date: 11-2004
Publisher: EDP Sciences
Date: 05-2019
DOI: 10.1051/0004-6361/201834230
Abstract: Aims. In this paper we discuss the radio continuum and X-ray properties of the so-far poorly studied Galactic supernova remnant (SNR) G5.9 + 3.1. Methods. We present the radio spectral energy distribution (SED) of the Galactic SNR G5.9 + 3.1 obtained with the Murchison Widefield Array (MWA). Combining these new observations with the surveys at other radio continuum frequencies, we discuss the integrated radio continuum spectrum of this particular remnant. We have also analyzed an archival XMM-Newton observation, which represents the first detection of X-ray emission from this remnant. Results. The SNR SED is very well explained by a simple power-law relation. The synchrotron radio spectral index of G5.9 + 3.1 is estimated to be 0.42 ± 0.03 and the integrated flux density at 1 GHz to be around 2.7 Jy. Furthermore, we propose that the identified point radio source, located centrally inside the SNR shell, is most probably a compact remnant of the supernova explosion. The shell-like X-ray morphology of G5.9 + 3.1 as revealed by XMM-Newton broadly matches the spatial distribution of the radio emission, where the radio-bright eastern and western rims are also readily detected in the X-ray while the radio-weak northern and southern rims are weak or absent in the X-ray. Extracted MOS1+MOS2+PN spectra from the whole SNR as well as the north, east, and west rims of the SNR are fit successfully with an optically thin thermal plasma model in collisional ionization equilibrium with a column density N H ~ 0.80 × 10 22 cm −2 and fitted temperatures spanning the range kT ~ 0.14–0.23 keV for all of the regions. The derived electron number densities n e for the whole SNR and the rims are also roughly comparable (ranging from ~0.20 f −1∕2 to ~0.40 f −1∕2 cm −3 , where f is the volume filling factor). We also estimate the swept-up mass of the X-ray emitting plasma associated with G5.9+3.1 to be ~46 f −1∕2 M ⊙ .
Publisher: Oxford University Press (OUP)
Date: 23-02-2015
DOI: 10.1093/MNRAS/STV079
Publisher: American Astronomical Society
Date: 20-11-2019
Publisher: American Astronomical Society
Date: 17-08-2009
Publisher: Oxford University Press (OUP)
Date: 29-04-2015
DOI: 10.1093/MNRAS/STV751
Publisher: Oxford University Press (OUP)
Date: 09-02-2018
DOI: 10.1093/MNRAS/STY346
Publisher: Oxford University Press (OUP)
Date: 15-11-2017
Publisher: American Astronomical Society
Date: 19-02-2004
DOI: 10.1086/382728
Publisher: Cambridge University Press (CUP)
Date: 2008
DOI: 10.1071/AS08003
Publisher: Cambridge University Press (CUP)
Date: 2018
DOI: 10.1017/PASA.2018.37
Abstract: We describe the motivation and design details of the ‘Phase II’ upgrade of the Murchison Widefield Array radio telescope. The expansion doubles to 256 the number of antenna tiles deployed in the array. The new antenna tiles enhance the capabilities of the Murchison Widefield Array in several key science areas. Seventy-two of the new tiles are deployed in a regular configuration near the existing array core. These new tiles enhance the surface brightness sensitivity of the array and will improve the ability of the Murchison Widefield Array to estimate the slope of the Epoch of Reionisation power spectrum by a factor of ∼3.5. The remaining 56 tiles are deployed on long baselines, doubling the maximum baseline of the array and improving the array u, v coverage. The improved imaging capabilities will provide an order of magnitude improvement in the noise floor of Murchison Widefield Array continuum images. The upgrade retains all of the features that have underpinned the Murchison Widefield Array’s success (large field of view, snapshot image quality, and pointing agility) and boosts the scientific potential with enhanced imaging capabilities and by enabling new calibration strategies.
Publisher: Oxford University Press (OUP)
Date: 25-09-2014
Publisher: American Astronomical Society
Date: 13-09-2018
Publisher: Oxford University Press (OUP)
Date: 10-2006
Publisher: Oxford University Press (OUP)
Date: 21-04-2010
Publisher: American Astronomical Society
Date: 20-03-2003
DOI: 10.1086/344477
Publisher: Oxford University Press (OUP)
Date: 03-02-2020
Abstract: We use spectral stacking to measure the contribution of galaxies of different masses and in different hierarchies to the cosmic atomic hydrogen (H i) mass density in the local Universe. Our s le includes 1793 galaxies at z & 0.11 observed with the Westerbork Synthesis Radio Telescope, for which Sloan Digital Sky Survey spectroscopy and hierarchy information are also available. We find a cosmic H i mass density of $\\Omega _{\\rm H\\, \\small {I} } = (3.99 \\pm 0.54)\\times 10^{-4} \\, h_{70}^{-1}$ at 〈 z〉 = 0.065. For the central and satellite galaxies, we obtain $\\Omega _{\\rm H\\, {\\small {I}}}$ of $(3.51 \\pm 0.49)\\times 10^{-4} \\, h_{70}^{-1}$ and $(0.90 \\pm 0.16)\\times 10^{-4} \\, h_{70}^{-1}$, respectively. We show that galaxies above and below stellar masses of ∼109.3 M⊙ contribute in roughly equal measure to the global value of $\\Omega _{\\rm H\\, \\small {I} }$. While consistent with estimates based on targeted H i surveys, our results are in tension with previous theoretical work. We show that these differences are, at least partly, due to the empirical recipe used to set the partition between atomic and molecular hydrogen in semi-analytical models. Moreover, comparing our measurements with the cosmological semi-analytic models of galaxy formation Shark and GALFORM reveals gradual stripping of gas via ram pressure works better to fully reproduce the properties of satellite galaxies in our s le than strangulation. Our findings highlight the power of this approach in constraining theoretical models and confirm the non-negligible contribution of massive galaxies to the H i mass budget of the local Universe.
Publisher: Oxford University Press (OUP)
Date: 11-07-2000
Publisher: Oxford University Press (OUP)
Date: 21-04-2006
Publisher: American Astronomical Society
Date: 06-2007
DOI: 10.1086/517867
Publisher: Cambridge University Press (CUP)
Date: 06-1996
DOI: 10.1017/S1323358000020919
Abstract: Several extragalactic H I surveys using a λ 21 cm 13-beam focal plane array will begin in early 1997 using the Parkes 64 m telescope. These surveys are designed to detect efficiently nearby galaxies that have failed to be identified optically because of low optical surface brightness or high optical extinction. We discuss scientific and technical aspects of the multibeam receiver, including astronomical objectives, feed, receiver and correlator design and data acquisition. A comparison with other telescopes shows that the Parkes multibeam receiver has significant speed advantages for any large-area λ 21 cm galaxy survey in the velocity range range 0–14000 km s −1 .
Publisher: EDP Sciences
Date: 09-2017
Publisher: EDP Sciences
Date: 09-2018
DOI: 10.1051/0004-6361/201833358
Abstract: We report the detection of a new Galactic bubble at the interface between the halo and the Galactic disc. We suggest that the nearby Lupus complex and parts of the Ophiuchus complex constitute the denser parts of the structure. This young bubble, ≲3 Myr old, could be the remnant of a supernova and it expands inside a larger HI loop that has been created by the outflows of the Upper Scorpius OB association. An HI cavity filled with hot X-ray gas is associated with the structure, which is consistent with the Galactic chimney scenario. The X-ray emission extends beyond the west and north-west edges of the bubble, suggesting that hot gas outflows are breaching the cavity, possibly through the fragmented Lupus complex. Analyses of the polarised radio synchrotron and of the polarised dust emission of the region suggest the connection of the Galactic centre spur with the young Galactic bubble. A distribution of HI clumps that spatially corresponds well to the cavity boundaries was found at V LSR ≃−100 km s −1 . Some of these HI clumps are forming jets, which may arise from the fragmented part of the bubble. We suggest that these clumps might be “dripping” cold clouds from the shell walls inside the cavity that is filled with hot ionised gas. It is possible that some of these clumps are magnetised and were then accelerated by the compressed magnetic field at the edge of the cavity. Such a mechanism would challenge the Galactic accretion and fountain model, where high-velocity clouds are considered to be formed at high Galactic latitude from hot gas flows from the Galactic plane.
Publisher: Oxford University Press (OUP)
Date: 19-07-2018
Publisher: American Astronomical Society
Date: 20-03-2004
DOI: 10.1086/381869
Publisher: American Astronomical Society
Date: 09-2000
DOI: 10.1086/301542
Publisher: American Astronomical Society
Date: 13-08-2014
Publisher: American Astronomical Society
Date: 07-2006
DOI: 10.1086/504685
Publisher: American Astronomical Society
Date: 06-09-2019
Publisher: Oxford University Press (OUP)
Date: 24-09-2013
Publisher: American Astronomical Society
Date: 04-2000
DOI: 10.1086/301303
Publisher: American Astronomical Society
Date: 31-10-2018
Publisher: American Astronomical Society
Date: 20-09-2006
DOI: 10.1086/504681
Publisher: American Astronomical Society
Date: 10-02-2006
DOI: 10.1086/498706
Publisher: American Astronomical Society
Date: 09-1994
DOI: 10.1086/117117
Publisher: Oxford University Press (OUP)
Date: 26-07-2012
Publisher: Oxford University Press (OUP)
Date: 03-03-2018
DOI: 10.1093/MNRAS/STY564
Publisher: Cambridge University Press (CUP)
Date: 2014
DOI: 10.1017/PASA.2013.36
Abstract: Archival data from the HI Parkes All-Sky Survey (HIPASS) and the HI Zone of Avoidance (HIZOA) survey have been carefully reprocessed into a new 1.4 GHz continuum map of the sky south of δ = +25°. The wide sky coverage, high sensitivity of 40 mK (limited by confusion), resolution of 14.4 arcmin (compared to 51 arcmin for the Haslam et al. 408 MHz and 35 arcmin for the Reich et al. 1.4 GHz surveys), and low level of artefacts make this map ideal for numerous studies, including: merging into interferometer maps to complete large-scale structures decomposition of thermal and non-thermal emission components from Galactic and extragalactic sources and comparison of emission regions with other frequencies. The new map is available for download.
Publisher: Oxford University Press (OUP)
Date: 17-08-2017
Publisher: American Astronomical Society
Date: 20-06-2007
DOI: 10.1086/517986
Publisher: American Astronomical Society
Date: 10-11-2014
Publisher: Oxford University Press (OUP)
Date: 21-07-2006
Publisher: Oxford University Press (OUP)
Date: 18-12-2014
Publisher: Cambridge University Press (CUP)
Date: 1998
DOI: 10.1071/AS98132
Abstract: The recently completed HI mosaic survey of the Large Magellanic Cloud (Kim et al. 1997) reveals complex structure in the interstellar medium, including filaments, arcs, holes and shells. We have catalogued giant and supergiant HI shells and searched for correlations with H α emission, using a new image taken with a camera lens mounted on the 16-inch telescope at Siding Spring Observatory.
Publisher: Oxford University Press (OUP)
Date: 1989
Publisher: Oxford University Press (OUP)
Date: 07-07-2006
Publisher: Springer Netherlands
Date: 2008
Publisher: Oxford University Press (OUP)
Date: 04-2013
DOI: 10.1093/MNRAS/STT555
Publisher: Cambridge University Press (CUP)
Date: 2008
DOI: 10.1071/AS07054
Abstract: With the ATNF Mopra telescope we are performing a survey in the 12 CO(1–0) line to map the molecular gas in the Large Magellanic Cloud. For some regions we also obtained interferometric maps of the high density gas tracers HCO + and HCN with the Australia Telescope Compact Array. Here we discuss the properties of the elongated molecular complex that stretches about 2 kpc southward from 30 Doradus. Our data suggest that the complex, which we refer to as the ‘molecular ridge’, is not a coherent feature but consists of many smaller clumps that share the same formation history. Likely triggers of molecular-cloud formation are shocks and shearing forces that are present in the surrounding south-eastern H i overdensity region, a region influenced by strong ram pressure and tidal forces. The molecular ridge is at the western edge of the the overdensity region where a bifurcated velocity structure transitions into a single disk velocity component. We find that the 12 CO(1–0) and H i emission peaks in the molecular ridge are typically near each other but never coincide. A likely explanation is the conversion of warmer, low-opacity H i to colder, high-opacity H i from which H 2 subsequently forms. On smaller scales we find that very dense molecular gas, as traced by interferometric HCO + and HCN maps, is associated with star formation along shocked filaments and with rims of expanding shell-like structures, both created by feedback from massive stars.
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: American Astronomical Society
Date: 02-03-2018
Publisher: American Astronomical Society
Date: 04-2009
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: 06-08-2015
Publisher: Oxford University Press (OUP)
Date: 07-2005
Publisher: Oxford University Press (OUP)
Date: 18-06-2018
Publisher: IOP Publishing
Date: 03-2021
DOI: 10.1088/1674-4527/21/2/30
Abstract: We report results from a neutral hydrogen (H i ) intensity mapping survey conducted with a Phased Array Feed (PAF) on the Parkes telescope. The survey was designed to cover ∼ 380 deg 2 over the redshift range 0.3 z 1 (a volume of ∼ 1.5 Gpc 3 ) in four fields covered by the WiggleZ Dark Energy Survey. The results presented here target a narrow redshift range of 0.73 z 0.78 where the effect of radio frequency interference (RFI) was less problematic. The data reduction and simulation pipeline was described, with an emphasis on flagging of RFI and correction for signal loss in the data reduction process, particularly due to the foreground subtraction methodology. A cross-correlation signal was detected between the H i intensity maps and the WiggleZ redshift data, with a mean litude of ⟨Δ T b δ opt ⟩ = 1.32 ± 0.42 mK (statistical errors only). A future Parkes cryogenic PAF is expected to detect the cross-correlation signal with higher accuracy than previously possible and allow measurement of the cosmic H i density at redshifts up to unity.
Publisher: American Astronomical Society
Date: 21-07-2008
Publisher: American Astronomical Society
Date: 2005
DOI: 10.1086/426320
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2021.5
Abstract: We present the South Galactic Pole (SGP) data release from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. These data combine both years of GLEAM observations at 72–231 MHz conducted with the Murchison Widefield Array (MWA) and cover an area of 5 113 $\\mathrm{deg}^{2}$ centred on the SGP at $20^{\\mathrm{h}} 40^{\\mathrm{m}} \\mathrm{RA} 05^{\\mathrm{h}} 04^{\\mathrm{m}}$ and $-48^{\\circ} \\mathrm{Dec} -2^{\\circ} $ . At 216 MHz, the typical rms noise is ${\\approx}5$ mJy beam –1 and the angular resolution ${\\approx}2$ arcmin. The source catalogue contains a total of 108 851 components above $5\\sigma$ , of which 77% have measured spectral indices between 72 and 231 MHz. Improvements to the data reduction in this release include the use of the GLEAM Extragalactic catalogue as a sky model to calibrate the data, a more efficient and automated algorithm to deconvolve the snapshot images, and a more accurate primary beam model to correct the flux scale. This data release enables more sensitive large-scale studies of extragalactic source populations as well as spectral variability studies on a one-year timescale.
Publisher: Oxford University Press (OUP)
Date: 29-10-2019
Publisher: Oxford University Press (OUP)
Date: 02-1987
Publisher: Oxford University Press (OUP)
Date: 27-09-2023
Publisher: Oxford University Press (OUP)
Date: 04-1988
Publisher: Oxford University Press (OUP)
Date: 23-07-2018
Publisher: American Astronomical Society
Date: 2006
DOI: 10.1086/508185
Publisher: Oxford University Press (OUP)
Date: 11-2005
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: American Astronomical Society
Date: 30-07-2010
Publisher: American Astronomical Society
Date: 20-06-2000
DOI: 10.1086/308953
Publisher: Oxford University Press (OUP)
Date: 11-11-2009
Publisher: Oxford University Press (OUP)
Date: 10-1995
Publisher: Oxford University Press (OUP)
Date: 05-2005
Publisher: Cambridge University Press (CUP)
Date: 1991
DOI: 10.1017/S1323358000023961
Abstract: III Zw 35 is a pair of galaxies characterised by intense OH maser emission, and powerful far-infrared and radio continuum. We have made a detailed study of the galaxy pair based on optical, infrared and radio observations. The brighter northern component is identified as a LINER or Seyfert galaxy and contains an active nuclear region from which radio continuum, OH maser and thermal dust emission are detected. We propose that the northern component has a compact active nucleus deeply embedded in an obscured region of diameter ~ 210 pc within which enhanced star-formation occurs. The lower luminosity, southern component is of low mass and is undergoing starburst activity over an extended region of diameter ~ 5.5 kpc. The origin of the starburst and non-thermal activity appears to be an interaction between the two components.
Publisher: Oxford University Press (OUP)
Date: 19-03-2015
DOI: 10.1093/MNRAS/STV273
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: American Astronomical Society
Date: 13-08-2009
Publisher: EDP Sciences
Date: 10-2018
DOI: 10.1051/0004-6361/201832768
Abstract: We have analyzed the southern sky emission in linear polarization at 2.3 GHz as observed by the S -band Polarization All Sky Survey ( S-PASS ). Our purpose is to study the properties of the diffuse Galactic polarized synchrotron as a contaminant to B -mode observations of the cosmic microwave background (CMB) polarization. We studied the angular distribution of the S-PASS signal at intermediate and high Galactic latitudes by means of the polarization angular power spectra. The power spectra, computed in the multipole interval 20 ≤ ℓ ≤ 1000, show a decay of the spectral litude as a function of multipole for ℓ ≲ 200, typical of the diffuse emission. At smaller angular scales, power spectra are dominated by the radio point source radiation. We find that, at low multipoles, spectra can be approximated by a power law C ℓ EE,BB ∝ ℓ α , with α ≃ −3, and characterized by a B -to- E ratio of about 0.5. We measured the polarized synchrotron spectral energy distribution (SED) in harmonic space, by combining S-PASS power spectra with low frequency WMAP and Planck ones, and by fitting their frequency dependence in six multipole bins, in the range 20 ≤ ℓ ≤ 140. Results show that the recovered SED, in the frequency range 2.3–33 GHz, is compatible with a power law with β s = −3.22 ± 0.08, which appears to be constant over the considered multipole range and in the different Galactic cuts. Combining the S-PASS total polarized intensity maps with those coming from WMAP and Planck we derived a map of the synchrotron spectral index β s at angular resolution of 2° on about 30% of the sky. The recovered β s distribution peaks at the value around −3.2. It exibits an angular power spectrum which can be approximated with a power law C ℓ ∝ ℓ γ with γ ≃ −2.6. We also measured a significant spatial correlation between synchrotron and thermal dust signals, as traced by the Planck 353 GHz channel. This correlation reaches about 40% on the larger angular scales, decaying considerably at the degree scales. Finally, we used the S-PASS maps to assess the polarized synchrotron contamination to CMB observations of the B -modes at higher frequencies. We ided the sky in small patches (with f sky ≃ 1%) and find that, at 90 GHz, the minimal contamination, in the cleanest regions of the sky, is at the level of an equivalent tensor-to-scalar ratio r synch ≃ 10 −3 . Moreover, by combining S-PASS data with Planck 353 GHz observations, we recover a map of the minimum level of total polarized foreground contamination to B -modes, finding that there is no region of the sky, at any frequency, where this contamination lies below equivalent tenor-to-scalar ratio r FG ≃ 10 −3 . This result confirms the importance of observing both high and low frequency foregrounds in CMB B -mode measurements.
Publisher: American Astronomical Society
Date: 15-10-2012
Publisher: Oxford University Press (OUP)
Date: 12-10-2020
Abstract: We present an analysis of the sky distribution of neutral hydrogen (H i) deficiency and spectral asymmetry for galaxies detected by the H i Parkes All-Sky Survey (HIPASS) as a function of projected environment density. Previous studies of galaxy H i deficiency using HIPASS were sensitive to galaxies that are extremely H i rich or poor. We use an updated binning statistic for measuring the global sky distribution of H i deficiency that is sensitive to the average deficiencies. Our analysis confirms the result from previous studies that galaxies residing in denser environments, such as Virgo, are on average more H i deficient than galaxies at lower densities. However, many other in idual groups and clusters are not found to be on average significantly H i poor, in contradiction to previous work. In terms of H i spectral asymmetries, we do not recover any significant trend of increasing asymmetry with environment density as found for other galaxy s les. We also investigate the correlation between H i asymmetry and deficiency, but find no variation in the mean asymmetry of galaxies that are H i rich, normal, or poor. This indicates that there is either no dependence of asymmetry on H i deficiency, or a galaxy’s H i deficiency only has a small influence on the measured H i asymmetry that we are unable to observe using only integrated spectra.
Publisher: Oxford University Press (OUP)
Date: 07-2005
Publisher: Springer Berlin Heidelberg
Date: 1998
DOI: 10.1007/BFB0104776
Publisher: Oxford University Press (OUP)
Date: 12-1989
Publisher: Cambridge University Press (CUP)
Date: 06-2007
DOI: 10.1017/S1743921307014421
Abstract: We present the Northern HIPASS Optical/Infrared Catalogue (NOIRCAT), an optical/near-infrared counterpart catalogue for the Northern HIPASS catalogue (NHICAT). Of the 1002 sources in NHICAT, 655 (66%) have optical counterparts with matching optical velocities. A further 87 sources have optical counterparts with matching velocities from previous radio emission line surveys. Assuming a dark galaxy to be an isolated H I source with no detectable stars, no candidate dark galaxies have been confirmed.
Publisher: Oxford University Press (OUP)
Date: 22-10-2019
Publisher: EDP Sciences
Date: 29-05-2014
Publisher: American Astronomical Society
Date: 02-11-2009
Publisher: Oxford University Press (OUP)
Date: 29-06-2018
Publisher: Oxford University Press (OUP)
Date: 12-1987
Publisher: Oxford University Press (OUP)
Date: 04-04-2012
Publisher: Oxford University Press (OUP)
Date: 15-11-1993
Publisher: American Astronomical Society
Date: 20-10-1999
DOI: 10.1086/307854
Publisher: Elsevier BV
Date: 03-2011
Publisher: Oxford University Press (OUP)
Date: 30-11-2016
Publisher: EDP Sciences
Date: 10-2010
Publisher: Cambridge University Press (CUP)
Date: 2017
DOI: 10.1017/PASA.2017.26
Abstract: The current generation of experiments aiming to detect the neutral hydrogen signal from the Epoch of Reionisation (EoR) is likely to be limited by systematic effects associated with removing foreground sources from target fields. In this paper, we develop a model for the compact foreground sources in one of the target fields of the MWA’s EoR key science experiment: the ‘EoR1’ field. The model is based on both the MWA’s GLEAM survey and GMRT 150 MHz data from the TGSS survey, the latter providing higher angular resolution and better astrometric accuracy for compact sources than is available from the MWA alone. The model contains 5 049 sources, some of which have complicated morphology in MWA data, Fornax A being the most complex. The higher resolution data show that 13% of sources that appear point-like to the MWA have complicated morphology such as double and quad structure, with a typical separation of 33 arcsec. We derive an analytic expression for the error introduced into the EoR two-dimensional power spectrum due to peeling close double sources as single point sources and show that for the measured source properties, the error in the power spectrum is confined to high k ⊥ modes that do not affect the overall result for the large-scale cosmological signal of interest. The brightest 10 mis-modelled sources in the field contribute 90% of the power bias in the data, suggesting that it is most critical to improve the models of the brightest sources. With this hybrid model, we reprocess data from the EoR1 field and show a maximum of 8% improved calibration accuracy and a factor of two reduction in residual power in k -space from peeling these sources. Implications for future EoR experiments including the SKA are discussed in relation to the improvements obtained.
Publisher: Oxford University Press (OUP)
Date: 21-12-2021
Abstract: The Arecibo Ultra-Deep Survey (AUDS) is a blind H i survey aimed at detecting galaxies beyond the local Universe in the 21-cm emission line of neutral hydrogen (H i). The Arecibo L-band Feed Array (ALFA) was used to image an area of 1.35 deg2 to a redshift depth of 0.16, using a total on-source integration time of over 700 h. The long integration time and small observation area makes it one of the most sensitive H i surveys, with a noise level of ∼75 μJy per 21.4 kHz (equivalent to 4.5 km s−1 at redshift z = 0). We detect 247 galaxies in the survey, more than doubling the number already detected in AUDS60. The mass range of detected galaxies is $\\log (M_{\\rm H\\,{\\small I}}~[h_{70}^{-2}\\, {\\rm M}_\\odot ]) = 6.32\\!-\\!10.76$. A modified maximum likelihood method is employed to construct an H i mass function (HIMF). The best fitting Schechter parameters are low-mass slope α = −1.37 ± 0.05, characteristic mass $\\log (M^*~[h_{70}^{-2}\\, {\\rm M}_\\odot ]) = 10.15 \\pm 0.09$, and density $\\Phi _* = (2.41 \\pm 0.57) \\times 10^{-3} h_{70}^3$ Mpc−3 dex−1. The s le was ided into low- and high-redshift bins to investigate the evolution of the HIMF. No change in low-mass slope α was measured, but an increased characteristic mass M*, was noted in the higher redshift s le. Using Sloan Digital Sky Survey data to define relative galaxy number density, the dependence of the HIMF with environment was also investigated in the two AUDS regions. We find no significant variation in α or M*. In the surveyed region, we measured a cosmic H i density $\\Omega _{\\rm H\\,{\\small I}} = (3.55 \\pm 0.30) \\times 10^{-4}\\, h_{70}^{-1}$. There appears to be no evolutionary trend in $\\Omega _{\\rm H\\,{\\small I}}$ above 2σ significance between redshifts of 0 and 0.16.
Publisher: Sissa Medialab
Date: 20-06-2014
DOI: 10.22323/1.207.0090
Publisher: Oxford University Press (OUP)
Date: 21-03-2009
Publisher: Oxford University Press (OUP)
Date: 05-11-2014
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: Oxford University Press (OUP)
Date: 25-07-2011
Publisher: American Astronomical Society
Date: 28-01-2013
Publisher: Oxford University Press (OUP)
Date: 27-06-2012
Publisher: Oxford University Press (OUP)
Date: 21-05-2013
DOI: 10.1093/MNRAS/STT747
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.9
Abstract: The Murchison Widefield Array (MWA) has observed the entire southern sky (Declination, $\delta 30^{\circ}$ ) at low radio frequencies, over the range 72–231MHz. These observations constitute the GaLactic and Extragalactic All-sky MWA (GLEAM) Survey, and we use the extragalactic catalogue (EGC) (Galactic latitude, $|b| ^{\circ}$ ) to define the GLEAM 4-Jy (G4Jy) S le. This is a complete s le of the ‘brightest’ radio sources ( $S_{\textrm{151\,MHz}} \,\text{Jy}$ ), the majority of which are active galactic nuclei with powerful radio jets. Crucially, low-frequency observations allow the selection of such sources in an orientation-independent way (i.e. minimising the bias caused by Doppler boosting, inherent in high-frequency surveys). We then use higher-resolution radio images, and information at other wavelengths, to morphologically classify the brightest components in GLEAM. We also conduct cross-checks against the literature and perform internal matching, in order to improve s le completeness (which is estimated to be $ .5$ %). This results in a catalogue of 1863 sources, making the G4Jy S le over 10 times larger than that of the revised Third Cambridge Catalogue of Radio Sources (3CRR $S_{\textrm{178\,MHz}} .9\,\text{Jy}$ ). Of these G4Jy sources, 78 are resolved by the MWA (Phase-I) synthesised beam ( $\sim2$ arcmin at 200MHz), and we label 67% of the s le as ‘single’, 26% as ‘double’, 4% as ‘triple’, and 3% as having ‘complex’ morphology at $\sim1\,\text{GHz}$ (45 arcsec resolution). We characterise the spectral behaviour of these objects in the radio and find that the median spectral index is $\alpha=-0.740 \pm 0.012$ between 151 and 843MHz, and $\alpha=-0.786 \pm 0.006$ between 151MHz and 1400MHz (assuming a power-law description, $S_{\nu} \propto \nu^{\alpha}$ ), compared to $\alpha=-0.829 \pm 0.006$ within the GLEAM band. Alongside this, our value-added catalogue provides mid-infrared source associations (subject to 6” resolution at 3.4 $\mu$ m) for the radio emission, as identified through visual inspection and thorough checks against the literature. As such, the G4Jy S le can be used as a reliable training set for cross-identification via machine-learning algorithms. We also estimate the angular size of the sources, based on their associated components at $\sim1\,\text{GHz}$ , and perform a flux density comparison for 67 G4Jy sources that overlap with 3CRR. Analysis of multi-wavelength data, and spectral curvature between 72MHz and 20GHz, will be presented in subsequent papers, and details for accessing all G4Jy overlays are provided at vw26/G4Jy .
Publisher: Cambridge University Press (CUP)
Date: 1997
DOI: 10.1071/AS97111
Abstract: The parameters of the H I Parkes All-Sky Surveys (HIPASS), as proposed by the Multibeam Survey Working Group, are described, as are the advantages and disadvantages of various multibeam observing techniques, including telescope scanning. The best techniques, in terms of minimising the variance in image sensitivity, are calculated. Some of the observing techniques may be applicable to other multibeam surveys.
Publisher: Oxford University Press (OUP)
Date: 10-2009
Publisher: Springer Science and Business Media LLC
Date: 29-10-2018
Publisher: Oxford University Press (OUP)
Date: 08-1997
Publisher: American Astronomical Society
Date: 15-01-2010
Publisher: American Astronomical Society
Date: 22-06-2017
Publisher: American Astronomical Society
Date: 10-1993
DOI: 10.1086/173223
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.2
Abstract: We describe an ultra-wide-bandwidth, low-frequency receiver recently installed on the Parkes radio telescope. The receiver system provides continuous frequency coverage from 704 to 4032 MHz. For much of the band ( ${\\sim}60\\%$ ), the system temperature is approximately 22 K and the receiver system remains in a linear regime even in the presence of strong mobile phone transmissions. We discuss the scientific and technical aspects of the new receiver, including its astronomical objectives, as well as the feed, receiver, digitiser, and signal processor design. We describe the pipeline routines that form the archive-ready data products and how those data files can be accessed from the archives. The system performance is quantified, including the system noise and linearity, beam shape, antenna efficiency, polarisation calibration, and timing stability.
Publisher: Cambridge University Press (CUP)
Date: 05-1996
DOI: 10.1017/S1323358000020798
Abstract: There are several excellent reasons for studying the Magellanic Clouds at millimetre wavelengths with a telescope such as the AT Mopra antenna: • The Magellanic Clouds are the nearest young, gas-rich galaxies to the Galaxy. They are therefore ideal places to study the processes which lead to star formation, and for comparing these processes with Galactic processes. • The distances of the Clouds are well established at close to 50 kpc for the LMC and 60 kpc for the SMC. • The Mopra beam at 2·6 mm (CO) corresponds to ~10 pc, which is comparable with the size of molecular clouds and complexes in the LMC and SMC (e.g. Rubio et al. 1993). The Mopra beam is also complementary to that obtainable at low frequencies with the AT Compact Array for continuum and HI studies (e.g. the 750 m configuration at 21 cm will give a resolution of ~12pc).
Publisher: Oxford University Press (OUP)
Date: 08-04-2019
DOI: 10.1093/MNRAS/STZ971
Publisher: American Astronomical Society
Date: 10-2003
DOI: 10.1086/376980
Publisher: Oxford University Press (OUP)
Date: 25-07-2019
Abstract: Using a spectral stacking technique, we measure the neutral hydrogen (H i) properties of a s le of galaxies at z 0.11 across 35 pointings of the Westerbork Synthesis Radio Telescope. The radio data contain 1895 galaxies with redshifts and positions known from the Sloan Digital Sky Survey. We carefully quantified the effects of s le bias, aperture used to extract spectra, sidelobes and weighting technique and use our data to provide a new estimate for the cosmic H i mass density. We find a cosmic H i mass density of $\\Omega _{\\rm H\\,{\\small I}} = (4.02 \\pm 0.26)\\times 10^{-4} h_{70}^{-1}$ at 〈z〉 = 0.066, consistent with measurements from blind H i surveys and other H i stacking experiments at low redshifts. The combination of the small interferometer beam size and the large survey volume makes our result highly robust against systematic effects due to confusion at small scales and cosmic variance at large scales. Splitting into three sub-s les with 〈z〉 = 0.038, 0.067, and 0.093 shows no significant evolution of the H i gas content at low redshift.
Publisher: Oxford University Press (OUP)
Date: 12-09-2017
Publisher: Oxford University Press (OUP)
Date: 06-2012
Publisher: Oxford University Press (OUP)
Date: 03-12-2013
Publisher: American Astronomical Society
Date: 20-11-1997
DOI: 10.1086/311000
Publisher: Oxford University Press (OUP)
Date: 03-03-2020
Abstract: We present an analysis of morphological, kinematic, and spectral asymmetries in observations of atomic neutral hydrogen (H i) gas from the Local Volume H i Survey (LVHIS), the VLA Imaging of Virgo in Atomic Gas (VIVA) survey, and the Hydrogen Accretion in Local Galaxies Survey. With the aim of investigating the impact of the local environment density and stellar mass on the measured H i asymmetries in future large H i surveys, we provide recommendations for the most meaningful measures of asymmetry for use in future analysis. After controlling for stellar mass, we find signs of statistically significant trends of increasing asymmetries with local density. The most significant trend we measure is for the normalized flipped spectrum residual (Aspec), with mean LVHIS and VIVA values of 0.204 ± 0.011 and 0.615 ± 0.068 at average weighted 10th nearest-neighbour galaxy number densities of log (ρ10/Mpc−3) = −1.64 and 0.88, respectively. Looking ahead to the Widefield ASKAP L-band Legacy All-sky Blind survey on the Australian Square Kilometre Array Pathfinder, we estimate that the number of detections will be sufficient to provide coverage over 5 orders of magnitude in both local density and stellar mass increasing the dynamic range and accuracy with which we can probe the effect of these properties on the asymmetry in the distribution of atomic gas in galaxies.
Publisher: Oxford University Press (OUP)
Date: 02-03-2011
Publisher: Cambridge University Press (CUP)
Date: 2017
DOI: 10.1017/PASA.2017.31
Abstract: The SKA and its pathfinders will enable studies of H i emission at higher redshifts than ever before. In moving beyond the local Universe, this will require the use of cosmologically appropriate formulae that have traditionally been simplified to their low-redshift approximations. In this paper, we summarise some of the most important relations for tracing H i emission in the SKA era, and present an online calculator to assist in the planning and analysis of observations ( hifi.icrar.org ).
Publisher: American Astronomical Society
Date: 20-04-1997
DOI: 10.1086/303917
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: Cambridge University Press (CUP)
Date: 1997
DOI: 10.1071/AS97246
Abstract: We report a search for the NH 3 (J,K) = (1,1) inversion line in the Large Magellanic Cloud (LMC) using the Parkes 64–m telescope. Candidate positions were chosen with the help of recent H i data from the Australia Telescope Compact Array and published 12 CO data from the Swedish–ESO Submillimetre Telescope. No detections of NH 3 in emission were found at the positions surveyed. Upper limits are approximately 25 to 74 mK.
Publisher: Cambridge University Press (CUP)
Date: 2017
DOI: 10.1017/PASA.2017.5
Abstract: The S -band Polarisation All-Sky Survey has observed the entire southern sky using the 64-m Parkes radio telescope at 2.3 GHz with an effective bandwidth of 184 MHz. The surveyed sky area covers all declinations δ ⩽ 0°. To analyse compact sources, the survey data have been re-processed to produce a set of 107 Stokes I maps with 10.75 arcmin resolution and the large scale emission contribution filtered out. In this paper, we use these Stokes I images to create a total intensity southern-sky extragalactic source catalogue at 2.3 GHz. The source catalogue contains 23 389 sources and covers a sky area of 16 600 deg 2 , excluding the Galactic plane for latitudes | b | 10°. Approximately, 8% of catalogued sources are resolved. S -band Polarisation All-Sky Survey source positions are typically accurate to within 35 arcsec. At a flux density of 225 mJy, the S -band Polarisation All-Sky Survey source catalogue is more than 95% complete, and ~ 94% of S -band Polarisation All-Sky Survey sources brighter than 500 mJy beam −1 have a counterpart at lower frequencies.
Publisher: Springer Berlin Heidelberg
Date: 2007
Publisher: World Scientific Pub Co Pte Ltd
Date: 12-2016
DOI: 10.1142/S2251171716410075
Abstract: HIPSR (HI-Pulsar) is a digital signal processing system for the Parkes 21-cm Multibeam Receiver that provides larger instantaneous bandwidth, increased dynamic range, and more signal processing power than the previous systems in use at Parkes. The additional computational capacity enables finer spectral resolution in wideband HI observations and real-time detection of Fast Radio Bursts during pulsar surveys. HIPSR uses a heterogeneous architecture, consisting of FPGA-based signal processing boards connected via high-speed Ethernet to high performance compute nodes. Low-level signal processing is conducted on the FPGA-based boards, and more complex signal processing routines are conducted on the GPU-based compute nodes. The development of HIPSR was driven by two main science goals: to provide large bandwidth, high-resolution spectra suitable for 21-cm stacking and intensity mapping experiments and to upgrade the Berkeley–Parkes–Swinburne Recorder (BPSR), the signal processing system used for the High Time Resolution Universe (HTRU) Survey and the Survey for Pulsars and Extragalactic Radio Bursts (SUPERB).
Publisher: Oxford University Press (OUP)
Date: 10-02-2016
DOI: 10.1093/MNRAS/STW105
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: American Astronomical Society
Date: 09-02-2016
Publisher: Cambridge University Press (CUP)
Date: 2015
DOI: 10.1017/PASA.2015.29
Abstract: We compare first-order (refractive) ionospheric effects seen by the MWA with the ionosphere as inferred from GPS data. The first-order ionosphere manifests itself as a bulk position shift of the observed sources across an MWA field of view. These effects can be computed from global ionosphere maps provided by GPS analysis centres, namely the CODE. However, for precision radio astronomy applications, data from local GPS networks needs to be incorporated into ionospheric modelling. For GPS observations, the ionospheric parameters are biased by GPS receiver instrument delays, among other effects, also known as receiver DCBs. The receiver DCBs need to be estimated for any non-CODE GPS station used for ionosphere modelling. In this work, single GPS station-based ionospheric modelling is performed at a time resolution of 10 min. Also the receiver DCBs are estimated for selected Geoscience Australia GPS receivers, located at Murchison Radio Observatory, Yarragadee, Mount Magnet and Wiluna. The ionospheric gradients estimated from GPS are compared with that inferred from MWA. The ionospheric gradients at all the GPS stations show a correlation with the gradients observed with the MWA. The ionosphere estimates obtained using GPS measurements show promise in terms of providing calibration information for the MWA.
Publisher: Cambridge University Press (CUP)
Date: 2015
DOI: 10.1017/PASA.2015.26
Abstract: GLEAM, the GaLactic and Extragalactic All-sky MWA survey, is a survey of the entire radio sky south of declination + 25° at frequencies between 72 and 231 MHz, made with the MWA using a drift scan method that makes efficient use of the MWA’s very large field-of-view. We present the observation details, imaging strategies, and theoretical sensitivity for GLEAM. The survey ran for two years, the first year using 40-kHz frequency resolution and 0.5-s time resolution the second year using 10-kHz frequency resolution and 2 s time resolution. The resulting image resolution and sensitivity depends on observing frequency, sky pointing, and image weighting scheme. At 154 MHz, the image resolution is approximately 2.5 × 2.2/cos (δ + 26.7°) arcmin with sensitivity to structures up to ~ 10° in angular size. We provide tables to calculate the expected thermal noise for GLEAM mosaics depending on pointing and frequency and discuss limitations to achieving theoretical noise in Stokes I images. We discuss challenges, and their solutions, that arise for GLEAM including ionospheric effects on source positions and linearly polarised emission, and the instrumental polarisation effects inherent to the MWA’s primary beam.
Publisher: Oxford University Press (OUP)
Date: 30-07-2016
Publisher: American Astronomical Society
Date: 07-2004
DOI: 10.1086/421744
Publisher: American Astronomical Society
Date: 12-03-2009
Publisher: Oxford University Press (OUP)
Date: 05-08-2019
Abstract: We investigate the possible presence of neutral hydrogen (H i) in intergalactic filaments at very low redshift (z ∼ 0.08), by stacking a set of 274 712 2dFGRS galaxy pairs over 21-cm maps obtained with dedicated observations conducted with the Parkes radio telescope, over a total sky area of approximately 1300 deg2 covering two patches in the northern and in the southern Galactic hemispheres. The stacking is performed by combining local maps in which each pair is brought to a common reference frame the resulting signal from the edge galaxies is then removed to extract the filament residual emission. We repeat the analysis on maps cleaned removing either 10 or 20 foreground modes in a principal component analysis. Our study does not reveal any clear H i excess in the considered filaments in either case we determine upper limits on the total filament H i brightness temperature at $T_{\\rm b} \\lesssim 10.3 \\, \\mu \\text{K}$ for the 10-mode and at $T_{\\rm b} \\lesssim 4.8 \\, \\mu \\text{K}$ for the 20-mode removed maps at the 95 per cent confidence level. These estimates translate into upper limits for the local filament H i density parameter, $\\Omega _{\\rm HI}^{\\rm (f)} \\lesssim 7.0\\times 10^{-5}$ and $\\Omega _{\\rm HI}^{\\rm (f)} \\lesssim 3.2\\times 10^{-5}$, respectively, and for the H i column density, $N_{\\rm HI} \\lesssim 4.6\\times 10^{15}\\, \\text{cm}^{-2}$ and $N_{\\rm HI} \\lesssim 2.1\\times 10^{15}\\, \\text{cm}^{-2}$, respectively. These column density constraints are consistent with previous detections of H i in the warm-hot intergalactic medium obtained observing broad Ly α absorption systems. This work shows for the first time how such constraints can be achieved using the stacking of galaxy pairs on 21-cm maps.
Publisher: Springer Science and Business Media LLC
Date: 02-1989
DOI: 10.1038/337625A0
Publisher: Oxford University Press (OUP)
Date: 09-11-2018
Publisher: Oxford University Press (OUP)
Date: 12-01-2013
DOI: 10.1093/MNRAS/STS637
Publisher: American Astronomical Society
Date: 08-2002
DOI: 10.1086/341582
Publisher: Oxford University Press (OUP)
Date: 10-1992
Publisher: American Astronomical Society
Date: 06-2003
DOI: 10.1086/374944
Publisher: Springer Science and Business Media LLC
Date: 1992
DOI: 10.1038/355147A0
Publisher: American Astronomical Society
Date: 04-1996
DOI: 10.1086/177000
Publisher: Cambridge University Press (CUP)
Date: 1999
DOI: 10.1071/AS99035
Abstract: The H I Parkes Zone of Avoidance Survey is a 21 cm blind search with the multibeam receiver on the 64-m radiotelescope, looking for galaxies hidden behind the southern Milky Way. The first, shallow (15 mJy rms) phase of the survey has uncovered 107 galaxies, two-thirds of which were previously unknown. The addition of these galaxies to existing extragalactic catalogues allows the connectivity of a very long, thin filament across the Zone of Avoidance within 3500 km s −1 to become evident. No local, hidden, very massive objects were uncovered. With similar results in the north (the Dwingeloo Obscured Galaxies Survey) our census of the most dynamically important H I -rich nearby galaxies is now complete, at least for those objects whose HI profiles are not totally buried in the Galactic H I signal. Tests are being devised to better quantify this remaining ZOA for blind HI searches. The full survey is ongoing, and is expected to produce a catalogue of thousands of objects when it is finished.
Publisher: American Astronomical Society
Date: 23-12-2019
Publisher: American Astronomical Society
Date: 10-2023
Publisher: Cambridge University Press (CUP)
Date: 1999
DOI: 10.1071/AS99152
Abstract: The Square Kilometre Array Radio Telescope is the next generation radio telescope. An international project is currently under way to design and build an instrument having an effective collecting area two orders of magnitude greater than that of any existing telescope. A number of separate studies are presently investigating how to design the Square Kilometre Array to best carry out the kinds of observations desired by the astronomical community. We present a summary of one of these studies, a workshop called The ‘Sub-microJansky Radio Sky’ held at the ATNF, Sydney, on 17 June 1998. This workshop addressed the nature of the radio sky at the very faint flux densities likely to be attainable by the Square Kilometre Array. In particular, each speaker investigated a separate population of radio sources and how the expected appearance of that population at such faint flux densities would dictate how to refine some of the design constraints for the Square Kilometre Array.
Publisher: Oxford University Press (OUP)
Date: 06-08-2021
Abstract: We have searched for weak fast radio burst (FRB) events using a data base containing 568 736 756 transient events detected using the Parkes radio telescope between 1997 and 2001. In order to classify these pulses, and to identify likely FRB candidates, we used a machine-learning algorithm based on ResNet. We identified 81 new candidate FRBs and provide details of their positions, event times, and dispersion measures. These events were detected in only one beam of the Parkes multibeam receiver. We used a relatively low S/N cut-off threshold when selecting these bursts and some have dispersion measures only slightly exceeding the expected Galactic contribution. We therefore present these candidate FRBs as a guide for follow-up observations in the search for repeating FRBs.
Publisher: American Astronomical Society
Date: 12-1998
DOI: 10.1086/300633
Publisher: Oxford University Press (OUP)
Date: 15-03-2017
DOI: 10.1093/MNRAS/STX642
Publisher: American Astronomical Society
Date: 07-2001
DOI: 10.1086/321735
Publisher: Oxford University Press (OUP)
Date: 12-04-2018
DOI: 10.1093/MNRAS/STY741
Publisher: Oxford University Press (OUP)
Date: 21-06-1997
Publisher: Oxford University Press (OUP)
Date: 11-1998
Publisher: Oxford University Press (OUP)
Date: 17-07-2014
Publisher: Oxford University Press (OUP)
Date: 22-09-2018
Publisher: Oxford University Press (OUP)
Date: 11-02-2003
Publisher: American Astronomical Society
Date: 10-1990
DOI: 10.1086/185846
Publisher: American Astronomical Society
Date: 27-05-2008
Publisher: Oxford University Press (OUP)
Date: 30-06-2015
Publisher: Oxford University Press (OUP)
Date: 04-1988
Publisher: American Astronomical Society
Date: 15-03-2013
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: Springer Science and Business Media LLC
Date: 11-1993
DOI: 10.1038/366136A0
Publisher: Cambridge University Press (CUP)
Date: 2004
DOI: 10.1071/AS04038
Abstract: We validate the baryonic Tully–Fisher (TF) relation by exploring the Tully–Fisher (TF) and BTF properties of optically and H i -selected disk galaxies. The data includes galaxies from Sakai et al. (2000) calibrator s le, McGaugh et al. (2000: M2000) I -band s le, and 18 newly acquired H i -selected field dwarf galaxies observed with the ANU 2.3-m telescope and the ATNF Parkes telescope (Gurovich 2005a). As in M2000, we re-cast the TF and BTF relations as relationships between baryon mass and W 20 . First we report some numerical errors in M2000. Then, we calculate weighted bi-variate linear fits to the data, and finally we compare the fits of the intrinsically fainter dwarfs with the brighter galaxies of Sakai et al. (2000). With regards to the local calibrator disk galaxies of Sakai et al. (2000), our results suggest that the BTF relation is indeed tighter than the TF relation and that the slopes of the BTF relations are statistically flatter than the equivalent TF relations. Further, for the fainter galaxies which include the I -band M2000 and H i -selected galaxies of Gurovich's s le, we calculate a break from a simple power law model because of what appears to be real cosmic scatter. Not withstanding this point, the BTF models are marginally better models than the equivalent TF ones with slightly smaller Χ red 2 values.
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: 08-04-2019
DOI: 10.1093/MNRAS/STZ956
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: 10-2002
DOI: 10.1086/342546
Publisher: American Astronomical Society
Date: 08-01-2008
DOI: 10.1086/528683
Publisher: Oxford University Press (OUP)
Date: 30-03-2019
DOI: 10.1093/MNRAS/STZ710
Publisher: American Astronomical Society
Date: 11-1996
DOI: 10.1086/118155
Publisher: Oxford University Press (OUP)
Date: 21-08-2003
Publisher: Oxford University Press (OUP)
Date: 10-09-2018
Publisher: Cambridge University Press (CUP)
Date: 2012
DOI: 10.1071/AS11013
Abstract: This is a design study into the capabilities of the Australian Square Kilometre Array Pathfinder in performing a full-sky low redshift neutral hydrogen survey, termed WALLABY, and the potential cosmological constraints one can attain from measurement of the galaxy power spectrum. We find that the full sky survey will likely attain 6 × 10 5 redshifts which, when combined with expected Planck CMB data, will constrain the Dark Energy equation of state to 20%, representing a coming of age for radio observations in creating cosmological constraints.
Publisher: American Astronomical Society
Date: 04-1995
DOI: 10.1086/117401
Publisher: Oxford University Press (OUP)
Date: 30-11-2019
Publisher: Oxford University Press (OUP)
Date: 09-2002
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: 15-09-1992
Publisher: Cambridge University Press (CUP)
Date: 2016
DOI: 10.1017/PASA.2016.19
Abstract: We have compiled a catalogue of H ii regions detected with the Murchison Widefield Array between 72 and 231 MHz. The multiple frequency bands provided by the Murchison Widefield Array allow us identify the characteristic spectrum generated by the thermal Bremsstrahlung process in H ii regions. We detect 306 H ii regions between 260° l 340° and report on the positions, sizes, peak, integrated flux density, and spectral indices of these H ii regions. By identifying the point at which H ii regions transition from the optically thin to thick regime, we derive the physical properties including the electron density, ionised gas mass, and ionising photon flux, towards 61 H ii regions. This catalogue of H ii regions represents the most extensive and uniform low frequency survey of H ii regions in the Galaxy to date.
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.16
Abstract: The FAST Ultra-Deep Survey (FUDS) is a blind survey that aims for the direct detection of H i in galaxies at redshifts $z .42$ . The survey uses the multibeam receiver on the Five-hundred-metre Aperture Spherical Telescope (FAST) to map six regions, each of size $0.72\\ \\textrm{deg}^2$ at high sensitivity ( ${\\sim}50\\,\\mu \\textrm{Jy}$ ) and high-frequency resolution (23 kHz). The survey will enable studies of the evolution of galaxies and their H i content with an eventual s le size of ${\\sim}1\\,000$ . We present the science goals, observing strategy, the effects of radio frequency interference at the FAST site, our mitigation strategies and the methods for calibration, data reduction and imaging as applied to initial data. The observations and reductions for the first field, FUDS0, are completed, with around 128 H i galaxies detected in a preliminary analysis. Ex le spectra are given in this paper, including a comparison with data from the overlapping GAL2577 field of Arecibo Ultra-Deep Survey.
Publisher: Springer Science and Business Media LLC
Date: 1990
DOI: 10.1038/343045A0
Publisher: American Astronomical Society
Date: 06-2006
DOI: 10.1086/503629
Publisher: Elsevier BV
Date: 08-1995
DOI: 10.1016/0167-8140(95)01599-C
Abstract: Dose-response relationships have been studied using an ordinal visual scale and reflectance spectrophotometry data from 123 treatment sites on 110 patients treated with 10 dose fractions over 12-14 days. Dose rates varied between 3 and 240 Gy/h and total doses of between 25 and 41 Gy were given using teletherapy apparatus. We found qualitative scoring of erythematous skin reactions to be subject to considerable inter- and intra-observer variation. Reflectance spectrophotometry provided more reproducible information, some of which was undetectable by naked eye. Baseline erythema readings were significantly higher in male patients and at anatomical sites of previous heavy UV exposure. In addition, a pronounced decline in erythema readings during the second week of therapy and 'reciprocal vicinity' (abscopal) effects adjacent to the field, undetected by the eye, were observed in a subset of patients. Meaningful dose-response relationships could be derived only from reflectance data with peak change from the pretreatment baseline measure providing the best discrimination. Peak erythema measures following treatment were found to depend on the age and gender of the patient as well as the treatment site and its baseline erythema measurement. This was independent of the total dose administered or the instantaneous dose rate at which it was delivered. The rate of erythema development was also dose rate dependent but only weakly dependent on the biological dose intensity (Gy equiv./day) of the treatment course. The data raise the question of whether irradiation-induced erythema is exclusively a secondary phenomenon occurring as a result of basal cell killing. The short repair half time value of 0.06 h obtained by direct analysis is perplexing and may reflect a dose rate-dependent physiological vasodilatory response to irradiation and/or a multi-component cellular repair process.
Publisher: Oxford University Press (OUP)
Date: 02-11-2015
Publisher: American Astronomical Society
Date: 05-1996
DOI: 10.1086/177222
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: American Astronomical Society
Date: 02-2002
DOI: 10.1086/338088
Publisher: Cambridge University Press (CUP)
Date: 1991
DOI: 10.1017/S1323358000025091
Abstract: The prompt radio emission associated with SN 1987A appeared and disappeared within the space of a few days. The next radio emission is expected as the high velocity ejecta expand into the circumstellar material. The evidence from the timing of the initial UV-flash is that this stage may occur shortly. We have therefore begun to monitor the field around SNR 1987A at high sensitivity with the Australia Telescope Compact Array. At λ 6cm, an upper limit to the radio emission of 180 μ Jy has been obtained. Continued observations are planned.
Publisher: Oxford University Press (OUP)
Date: 05-09-2019
DOI: 10.1093/MNRAS/STZ806
Abstract: We present the S-Band Polarization All Sky Survey (S-PASS), a survey of polarized radio emission over the southern sky at Dec. & −1° taken with the Parkes radio telescope at 2.3 GHz. The main aim was to observe at a frequency high enough to avoid strong depolarization at intermediate Galactic latitudes (still present at 1.4 GHz) to study Galactic magnetism, but low enough to retain le signal-to-noise ratio (S/N) at high latitudes for extragalactic and cosmological science. We developed a new scanning strategy based on long azimuth scans and a corresponding map-making procedure to make recovery of the overall mean signal of Stokes Q and U possible, a long-standing problem with polarization observations. We describe the scanning strategy, map-making procedure and validation tests. The overall mean signal is recovered with a precision better than 0.5 per cent. The maps have a mean sensitivity of 0.81 mK on beam-size scales and show clear polarized signals, typically to within a few degrees of the Galactic plane, with le S/N everywhere (the typical signal in low-emission regions is 13 mK and 98.6 per cent of pixels have S/N & 3). The largest depolarization areas are in the inner Galaxy, associated with the Sagittarius Arm. We have also computed a rotation measure map combining S-PASS with archival data from the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck experiments. A Stokes I map has been generated, with sensitivity limited to the confusion level of 9 mK.
Publisher: Oxford University Press (OUP)
Date: 11-09-2006
Publisher: American Astronomical Society
Date: 25-03-2014
Publisher: Springer Science and Business Media LLC
Date: 08-1998
DOI: 10.1038/29466
Publisher: American Astronomical Society
Date: 03-2004
DOI: 10.1086/381905
Publisher: Oxford University Press (OUP)
Date: 02-2005
Publisher: Oxford University Press (OUP)
Date: 25-03-2017
DOI: 10.1093/MNRAS/STX746
Publisher: American Astronomical Society
Date: 12-1999
DOI: 10.1086/301145
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.23
Abstract: A plausible formation scenario for the Galactic globular clusters 47 Tucanae (47 Tuc) and Omega Centauri $(\\omega$ Cen) is that they are tidally stripped remnants of dwarf galaxies, in which case they are likely to have retained a fraction of their dark matter cores. In this study, we have used the ultra-wide band receiver on the Parkes telescope (Murriyang) to place upper limits on the annihilation rate of exotic Light Dark Matter particles $(\\chi)$ via the $\\chi\\chi\\rightarrow e^+e^-$ channel using measurements of the recombination rate of positronium (Ps). This is an extension of a technique previously used to search for Ps in the Galactic Centre. However, by stacking of spectral data at multiple line frequencies, we have been able to improve sensitivity. Our measurements have resulted in $3-\\sigma$ flux density (recombination rate) upper limits of 1.7 mJy $\\left(1.4\\times 10^{43}\\, \\mathrm{s}^{-1}\\right)$ and 0.8 mJy $\\left(1.1 \\times 10^{43} \\mathrm{s}^{-1}\\right)$ for 47 Tuc and $\\omega$ Cen, respectively. Within the Parkes beam at the cluster distances, which varies from 10–23 pc depending on the frequency of the recombination line, and for an assumed annihilation cross-section $\\langle\\sigma v\\rangle = 3\\times 10^{-29} \\mathrm{cm}^3\\, \\mathrm{s}^{-1}$ , we calculate upper limits to the dark matter mass and rms dark matter density of ${\\lesssim} 1.2-1.3\\times 10^5 f_n^{-0.5}$ $\\left(m_\\chi/\\mathrm{MeV\\, c}^{-2}\\right)$ $\\mathrm{M}_{\\odot}$ and ${\\lesssim} 48-54 f_n^{-0.5}$ $\\left(m_\\chi/\\mathrm{MeV\\, c}^{-2}\\right)$ $\\mathrm{M}_{\\odot} \\mathrm{pc}^{-3}$ for the clusters, where $f_n=R_n/R_p$ is the ratio of Ps recombination transitions to annihilations, estimated to be ${\\sim}0.01$ . The radio limits for $\\omega$ Cen suggest that, for a fiducial dark/luminous mass ratio of ${\\sim}0.05$ , any contribution from Light Dark Matter is small unless $\\langle\\sigma v\\rangle 7.9\\times 10^{-28}\\ \\left(m_\\chi/\\mathrm{MeV\\, c}^{-2}\\right)^2 \\mathrm{cm}^3 \\mathrm{s}^{-1}$ . Owing to the compactness and proximity of the clusters, archival 511-keV measurements suggest even tighter limits than permitted by CMB anisotropies, $\\langle\\sigma v\\rangle 8.6\\times 10^{-31}\\ (m_\\chi/\\mathrm{MeV\\, c}^{-2})^2 \\mathrm{cm}^3 \\mathrm{s}^{-1}$ . Due to the very low synchrotron radiation background, our recombination rate limits substantially improve on previous radio limits for the Milky Way.
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: American Astronomical Society
Date: 29-06-2018
Publisher: American Association for the Advancement of Science (AAAS)
Date: 11-03-2005
Abstract: We have measured the Faraday rotation toward a large s le of polarized radio sources behind the Large Magellanic Cloud (LMC) to determine the structure of this galaxy's magnetic field. The magnetic field of the LMC consists of a coherent axisymmetric spiral of field strength ∼1 microgauss. Strong fluctuations in the magnetic field are also seen on small ( .5 parsec) and large (∼100 parsecs) scales. The large bursts of recent star formation and supernova activity in the LMC argue against standard dynamo theory, adding to the growing evidence for rapid field lification in galaxies.
Publisher: American Astronomical Society
Date: 13-01-2009
Publisher: Oxford University Press (OUP)
Date: 07-02-2013
DOI: 10.1093/MNRAS/STT030
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2021.36
Abstract: The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) is a radio continuum survey at 76–227 MHz of the entire southern sky (Declination $ \\!{+}30^{\\circ}$ ) with an angular resolution of ${\\approx}2$ arcmin. In this paper, we combine GLEAM data with optical spectroscopy from the 6dF Galaxy Survey to construct a s le of 1 590 local (median $z \\approx 0.064$ ) radio sources with $S_{200\\,\\mathrm{MHz}} 55$ mJy across an area of ${\\approx}16\\,700\\,\\mathrm{deg}^{2}$ . From the optical spectra, we identify the dominant physical process responsible for the radio emission from each galaxy: 73% are fuelled by an active galactic nucleus (AGN) and 27% by star formation. We present the local radio luminosity function for AGN and star-forming (SF) galaxies at 200 MHz and characterise the typical radio spectra of these two populations between 76 MHz and ${\\sim}1$ GHz. For the AGN, the median spectral index between 200 MHz and ${\\sim}1$ GHz, $\\alpha_{\\mathrm{high}}$ , is $-0.600 \\pm 0.010$ (where $S \\propto \\nu^{\\alpha}$ ) and the median spectral index within the GLEAM band, $\\alpha_{\\mathrm{low}}$ , is $-0.704 \\pm 0.011$ . For the SF galaxies, the median value of $\\alpha_{\\mathrm{high}}$ is $-0.650 \\pm 0.010$ and the median value of $\\alpha_{\\mathrm{low}}$ is $-0.596 \\pm 0.015$ . Among the AGN population, flat-spectrum sources are more common at lower radio luminosity, suggesting the existence of a significant population of weak radio AGN that remain core-dominated even at low frequencies. However, around 4% of local radio AGN have ultra-steep radio spectra at low frequencies ( $\\alpha_{\\mathrm{low}} -1.2$ ). These ultra-steep-spectrum sources span a wide range in radio luminosity, and further work is needed to clarify their nature.
Publisher: Oxford University Press (OUP)
Date: 11-02-2003
Publisher: American Astronomical Society
Date: 20-08-1998
DOI: 10.1086/306030
Publisher: Oxford University Press (OUP)
Date: 07-06-2006
Publisher: American Astronomical Society
Date: 23-06-2004
DOI: 10.1086/423239
Publisher: American Astronomical Society
Date: 05-2022
Abstract: In the local universe, OH megamasers (OHMs) are detected almost exclusively in infrared-luminous galaxies, with a prevalence that increases with IR luminosity, suggesting that they trace gas-rich galaxy mergers. Given the proximity of the rest frequencies of OH and the hyperfine transition of neutral atomic hydrogen (H i ), radio surveys to probe the cosmic evolution of H i in galaxies also offer exciting prospects for exploiting OHMs to probe the cosmic history of gas-rich mergers. Using observations for the Looking At the Distant Universe with the MeerKAT Array (LADUMA) deep H i survey, we report the first untargeted detection of an OHM at z 0.5, LADUMA J033046.20−275518.1 (nicknamed “Nkalakatha”). The host system, WISEA J033046.26−275518.3, is an infrared-luminous radio galaxy whose optical redshift z ≈ 0.52 confirms the MeerKAT emission-line detection as OH at a redshift z OH = 0.5225 ± 0.0001 rather than H i at lower redshift. The detected spectral line has 18.4 σ peak significance, a width of 459 ± 59 km s −1 , and an integrated luminosity of (6.31 ± 0.18 [statistical] ± 0.31 [systematic]) × 10 3 L ⊙ , placing it among the most luminous OHMs known. The galaxy’s far-infrared luminosity L FIR = (1.576 ±0.013) × 10 12 L ⊙ marks it as an ultraluminous infrared galaxy its ratio of OH and infrared luminosities is similar to those for lower-redshift OHMs. A comparison between optical and OH redshifts offers a slight indication of an OH outflow. This detection represents the first step toward a systematic exploitation of OHMs as a tracer of galaxy growth at high redshifts.
Publisher: American Astronomical Society
Date: 27-03-2017
Publisher: Springer Netherlands
Date: 2008
Publisher: Oxford University Press (OUP)
Date: 21-12-2008
Publisher: AIP
Date: 2007
DOI: 10.1063/1.2803627
Publisher: Elsevier BV
Date: 06-2015
DOI: 10.1016/J.WATRES.2015.03.007
Abstract: A series of dynamic-flow kinetic experiments were conducted to assess the removal rates of aqueous Cu(2+) and Zn(2+) ions by zero-valent iron (ZVI), a promising material for inclusion in cold-climate remediation applications. The influence of experimental parameters on contaminant removal rates, including aqueous flow rate, operating temperature, and the concentrations of ZVI, salt and dissolved oxygen, was investigated. A mass transport model has been developed that accounts (i) aqueous-phase dispersion processes, (ii) film diffusion of contaminant ions to the reactive ZVI surface and (iii) the reactive removal mechanism itself. Regression to the experimental data indicated that when oxygen is present in the solution feed Cu(2+) and Zn(2+) removal processes were limited by film diffusion. In de-aerated solutions film diffusion still controls Cu(2+) removal but a first-order surface reaction provides a better model for Zn(2+) kinetics. Using air as the equilibrium feed gas, the reactive proportion of the total surface area for contaminant removal was calculated to be 97% and 64% of the active spherically-assumed geometric area associated with ZVI media for Cu(2+) and Zn(2+), respectively. Relative to a gas absorption area, determined in previous studies, the reactive proportion is less than 0.41% of the unreacted ZVI total surface area. These findings suggest that only part of the iron oxyhydroxide surface is reacting during ZVI based metal contaminant removal.
Publisher: EDP Sciences
Date: 09-2016
Publisher: American Astronomical Society
Date: 16-12-2019
Publisher: American Astronomical Society
Date: 03-1996
DOI: 10.1086/176920
Publisher: Cambridge University Press (CUP)
Date: 02-2017
DOI: 10.1017/S1743921317005312
Abstract: Supernova remnants (SNRs) are powerful particle accelerators. As a supernova (SN) blast wave propagates through the circumstellar medium (CSM), electrons and protons scatter across the shock and gain energy by entrapment in the magnetic field. The accelerated particles generate further magnetic field fluctuations and local lification, leading to cosmic ray production. The wealth of data from Supernova 1987A is providing a template of the SN-CSM interaction, and an important guide to the radio detection and identification of core-collapse SNe based on their spectral properties. Thirty years after the explosion, radio observations of SNR 1987A span from 70 MHz to 700 GHz. We review extensive observing c aigns with the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA), and follow-ups with other radio telescopes. Observations across the radio spectrum indicate rapid changes in the remnant morphology, while current ATCA and ALMA observations show that the SNR has entered a new evolutionary phase.
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: 05-2008
End Date: 12-2011
Amount: $1,430,000.00
Funder: Australian Research Council
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Amount: $160,000.00
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Amount: $556,800.00
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Amount: $1,355,000.00
Funder: Australian Research Council
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Amount: $1,150,000.00
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Amount: $556,800.00
Funder: Australian Research Council
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Funder: Australian Research Council
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Amount: $494,000.00
Funder: Australian Research Council
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End Date: 07-2014
Amount: $278,400.00
Funder: Australian Research Council
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End Date: 03-2017
Amount: $1,000,000.00
Funder: Australian Research Council
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Amount: $20,600,000.00
Funder: Australian Research Council
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Amount: $350,000.00
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Amount: $30,300,000.00
Funder: Australian Research Council
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