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Astronomical and Space Sciences | Cosmology and Extragalactic Astronomy
Publisher: American Astronomical Society
Date: 30-09-2021
Publisher: Wiley
Date: 02-2016
Abstract: The Lockman Hole Project is a wide international collaboration aimed at exploiting the multi‐band extensive and deep information available for the Lockman Hole region, with the aim of better characterizing the physical and evolutionary properties of the various source populations detected in deep radio fields. Recent observations with the LOw‐Frequency ARray (LOFAR) extends the multi‐frequency radio information currently available for the Lockman Hole (from 350 MHz up to 15 GHz) down to 150 MHz, allowing us to explore a new radio spectral window for the faint radio source population. These LOFAR observations allow us to study the population of sources with spectral peaks at lower radio frequencies, providing insight into the evolution of GPS and CSS sources. In this general framework, I present preliminary results from 150 MHz LOFAR observations of the Lockman Hole field. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Publisher: Oxford University Press (OUP)
Date: 20-07-2016
Publisher: Oxford University Press (OUP)
Date: 25-10-2021
Abstract: We present results from a search for the H i 21-cm line in absorption towards 16 bright radio sources with the six-antenna commissioning array of the Australian Square Kilometre Array Pathfinder. Our targets were selected from the 2-Jy s le, a flux-limited survey of the southern radio sky with extensive multiwavelength follow-up. Two sources were detected in H i absorption including a new detection towards the bright Fanaroff–Riley Type II radio galaxy PKS 0409−75 at a redshift of $z$ = 0.674. The H i absorption line is blueshifted by ∼3300 km s−1 compared to the optical redshift of the host galaxy of PKS 0409−75 at $z$ = 0.693. Deep optical imaging and spectroscopic follow-up with the GMOS instrument on the Gemini-South telescope reveal that the H i absorption is associated with a galaxy in front of the southern radio lobe with a stellar mass of 3.2–6.8 × 1011 M⊙, a star formation rate of ∼1.24 M⊙ yr−1, and an estimated H i column density of 2.16 × 1021 cm−2, assuming a spin temperature of Tspin = 500 K and source covering factor of Cf = 0.3. Using polarization measurements of PKS 0409−75 from the literature, we estimate the magnetic field of the absorbing galaxy to be ∼14.5 $\\mu$G, consistent with field strengths observed in nearby spiral galaxies but larger than expected for an elliptical galaxy. Results from this pilot study can inform future surveys as new wide-field telescopes allow us to search for 21-cm H i absorption towards all bright radio sources as opposed to smaller targeted s les.
Publisher: Springer International Publishing
Date: 2018
Publisher: Cambridge University Press (CUP)
Date: 09-2014
DOI: 10.1017/S1743921315002343
Abstract: The tight correlations observed between galaxies and their SMBH provides compelling evidence that the evolution of the galaxy and its central black hole are strongly linked. This is generally attributed to feedback mechanisms which, according to simulations, often take the form of outflows of gas, quenching star formation in the host galaxy and halting accretion onto the central black hole. While there are a number of plausible ways that outflows could be produced, recent results have shown that in some cases radio jets could be responsible for driving fast outflows of gas. One such ex le is seen in the nearby radio galaxy 3C293. In this talk I will present results from JVLA radio observations where we detect fast outflows (~1200 km/s) of neutral gas which are being driven by the radio-jet approximately 0.5 kpc from the central core, providing direct evidence for jet-ISM interaction. This is accompanied with recent IFU observations showing that ionised gas outflows are also being driven by the radio jet. Pinpointing the location of these outflows enables us to derive crucial parameters, such as the mass outflow rates and kinetic energy involved, which we can compare to predictions from galaxy evolution simulations.
Publisher: Oxford University Press (OUP)
Date: 12-2014
Publisher: American Astronomical Society
Date: 02-07-2010
Publisher: American Astronomical Society
Date: 29-10-2018
Publisher: Oxford University Press (OUP)
Date: 24-02-2020
Abstract: Past studies of compact active galactic nuclei (AGNs), the dominant population at high radio frequencies, selected them using flat spectral index criteria. This biases the s le due to the steepening of AGN spectra at high radio frequencies. We improve upon this by selecting 3610 compact AGNs using their angular size information ($\\lesssim$0.15 arcsec scale) from the Australia Telescope 20 GHz (AT20G) high-angular resolution catalogue. We cross-match these against the Wide-field Infrared Survey Explorer AllWISE catalogue and present a catalogue with 3300 (91 per cent) matches, 91 (3 per cent) rejects, and 219 (6 per cent) non-detections that are excellent high-redshift candidates. Of the matched compact AGNs, 92 per cent exhibit QSO mid-infrared colours (W1−W2 & 0.5). Therefore, our s le of high frequency compact sources has a very high rate of identification with mid-infrared QSOs. We find counterparts for 88 per cent of 387 compact steep-spectrum (CSS) sources in the AT20G survey, 82 ± 5 per cent of which exhibit QSO mid-infrared colours and have moderate redshifts (zmedian = 0.82), while those dominated by host galaxy colours in mid-infrared have lower redshifts (zmedian = 0.13). The latter classified into late- and early-type galaxies using their mid-infrared colours shows a majority (68 ± 4 per cent) have colours characteristic of late-type galaxies. Thus, we find that a larger fraction of these CSS sources are embedded in hosts with higher gas densities than average early-type galaxies. We compare mid-infrared colours of our AGNs against those reported for AGNs primarily selected using non-radio techniques. This shows that mid-infrared SED of high frequency selected compact radio AGN is comparatively less red, possibly due to contributions from their hosts.
Publisher: Oxford University Press (OUP)
Date: 17-03-2016
DOI: 10.1093/MNRAS/STW638
Abstract: Due to their steep spectra, low-frequency observations of Fanaroff-Riley type II (FR II) radio galaxies potentially provide key insights in to the morphology, energetics and spectrum of these powerful radio sources. However, limitations imposed by the previous generation of radio interferometers at metre wavelengths have meant that this region of parameter space remains largely unexplored. In this paper, the first in a series examining FR IIs at low frequencies, we use LOFAR (LOw Frequency ARray) observations between 50 and 160 MHz, along with complementary archival radio and X-ray data, to explore the properties of two FR II sources, 3C 452 and 3C 223. We find that the morphology of 3C 452 is that of a standard FR II rather than of a double-double radio galaxy as had previously been suggested, with no remnant emission being observed beyond the active lobes. We find that the low-frequency integrated spectra of both sources are much steeper than expected based on traditional assumptions and, using synchrotron/inverse-Compton model fitting, show that the total energy content of the lobes is greater than previous estimates by a factor of around 5 for 3C 452 and 2 for 3C 223. We go on to discuss possible causes of these steeper-than-expected spectra and provide revised estimates of the internal pressures and magnetic field strengths for the intrinsically steep case. We find that the ratio between the equipartition magnetic field strengths and those derived through synchrotron/inverse-Compton model fitting remains consistent with previous findings and show that the observed departure from equipartition may in some cases provide a solution to the spectral versus dynamical age disparity.
Publisher: Oxford University Press (OUP)
Date: 24-10-2019
Publisher: Oxford University Press (OUP)
Date: 14-01-2014
Publisher: Cambridge University Press (CUP)
Date: 10-2014
DOI: 10.1017/S1743921314003780
Abstract: Until recently, the radio sky above 5 GHz was relatively unexplored. This has changed with the completion of the Australia Telescope 20 GHz survey (AT20G Murphy et al ., 2010) a blind survey of the southern sky down to a limiting flux density of 40 mJy. The AT20G survey provides by far the largest and most complete s le of high-frequency radio sources yet obtained, offering new insights into the nature of the high-frequency active galaxy population. Whilst the radio data provides a unique s le of objects, these data alone are insufficient to completely constrain models of radio source properties and the evolution of radio galaxies. Complementary multiwavelength data is vital in understanding the physical properties of the central black hole. In this talk I will provide a brief overview of the AT20G survey, followed by a discussion of the multiwavelength properties of the high-frequency source population. In particular, I will focus on the optical properties of AT20G sources, which are very different to those of a low-frequency selected s le, along with the gamma-ray properties where we find a correlation between high-frequency radio flux density and gamma-ray flux density. By studying the multiwavelength properties of a large s le of high-frequency radio sources we gain a unique perspective on the inner dynamics of some of the most active AGN.
Publisher: Oxford University Press (OUP)
Date: 25-08-2015
Publisher: Oxford University Press (OUP)
Date: 17-01-2018
DOI: 10.1093/MNRAS/STY026
Publisher: Oxford University Press (OUP)
Date: 07-11-2016
Publisher: Oxford University Press (OUP)
Date: 05-09-2016
Publisher: Oxford University Press (OUP)
Date: 10-10-2011
Publisher: American Astronomical Society
Date: 24-09-2020
Publisher: American Astronomical Society
Date: 10-2023
Publisher: EDP Sciences
Date: 10-2017
Publisher: Oxford University Press (OUP)
Date: 12-05-2014
DOI: 10.1093/MNRAS/STU708
Publisher: Cambridge University Press (CUP)
Date: 08-2018
DOI: 10.1017/S1743921319003491
Abstract: Radio jets can play multiple roles in the feedback loop by regulating the accretion of the gas, by enhancing gas turbulence, and by driving gas outflows. Numerical simulations are beginning to make detailed predictions about these processes. Using high resolution VLBI observations we test these predictions by studying how radio jets of different power and in different phases of evolution affect the properties and kinematics of the surrounding H I gas. Consistent with predictions, we find that young (or recently restarted) radio jets have stronger impact as shown by the presence of H I outflows. The outflowing medium is clumpy with clouds of with sizes up to a few tens of pc and mass ∼ 10 4 M ȯ ) already in the region close to the nucleus ( 100 pc), making the jet interact strongly and shock the surrounding gas. We present a case of a low-power jet where, as suggested by the simulations, the injection of energy may produce an increase in the turbulence of the medium instead of an outflow.
Publisher: Oxford University Press (OUP)
Date: 21-03-2022
Abstract: We present results from MUSE observations of a 21-cm ${\\rm H\\, {\\small I}}$ absorption system detected with the Australian Square Kilometre Array Pathfinder radio telescope at redshift z = 0.4503 towards the z = 1.71 quasar PKS 1610-771. We identify four galaxies (A, B, X, and Y) at the same redshift as the 21-cm ${\\rm H\\, {\\small I}}$ D ed Lyman-α (DLA) absorption system, with impact parameters ranging from less than 10 kpc to almost 200 kpc from the quasar sightline. ${\\rm Ca\\, {\\small II}}$ and ${\\rm Na\\, {\\small I}}$ absorption is seen in the MUSE spectrum of the background QSO, with velocities coinciding with the initial ${\\rm H\\, {\\small I}}$ 21-cm detection, but tracing less dense and warmer gas. This metal-line component aligns with the rotating ionized disc of galaxy B (impact parameter 18 kpc from the QSO) and appears to be corotating with the galaxy disc. In contrast, the 21-cm ${\\rm H\\, {\\small I}}$ absorber is blueshifted relative to the galaxies nearest the absorber and has the opposite sign to the velocity field of galaxy B. Since galaxies A and B are separated by only 17 kpc on the sky and 70 km s−1 in velocity, it appears likely that the 21-cm detection traces extragalactic clouds of gas formed from their interaction. This system reveals that the cold 100 K neutral gas critical for star formation can be associated with complex structures beyond the galaxy disc, and is a first case study made in preparation for future large 21-cm absorption surveys like the ASKAP First Large Absorption Survey in ${\\rm H\\, {\\small I}}$.
Publisher: Oxford University Press (OUP)
Date: 11-02-2014
Publisher: Oxford University Press (OUP)
Date: 04-04-2012
Publisher: Oxford University Press (OUP)
Date: 25-08-2010
Publisher: Oxford University Press (OUP)
Date: 10-11-2018
Publisher: Oxford University Press (OUP)
Date: 28-06-2019
Abstract: The Parkes Pulsar Timing Array (PPTA) project monitors two dozen millisecond pulsars (MSPs) in order to undertake a variety of fundamental physics experiments using the Parkes 64-m radio telescope. Since 2017 June, we have been undertaking commensal searches for fast radio bursts (FRBs) during the MSP observations. Here, we report the discovery of four FRBs (171209, 180309, 180311, and 180714). The detected events include an FRB with the highest signal-to-noise ratio ever detected at the Parkes Observatory, which exhibits unusual spectral properties. All four FRBs are highly polarized. We discuss the future of commensal searches for FRBs at Parkes.
Publisher: American Astronomical Society
Date: 24-08-2023
Abstract: We present a comprehensive catalog of observations and stellar population properties for 23 highly secure host galaxies of fast radio bursts (FRBs). Our s le comprises 6 repeating FRBs and 17 apparent nonrepeaters. We present 82 new photometric and 8 new spectroscopic observations of these hosts. Using stellar population synthesis modeling and employing nonparametric star formation histories (SFHs), we find that FRB hosts have a median stellar mass of ≈10 9.9 M ⊙ , mass-weighted age ≈5.1 Gyr, and ongoing star formation rate ≈1.3 M ⊙ yr −1 but span wide ranges in all properties. Classifying the hosts by degree of star formation, we find that 87% (20 of 23 hosts) are star-forming, two are transitioning, and one is quiescent. The majority trace the star-forming main sequence of galaxies, but at least three FRBs in our s le originate in less-active environments (two nonrepeaters and one repeater). Across all modeled properties, we find no statistically significant distinction between the hosts of repeaters and nonrepeaters. However, the hosts of repeating FRBs generally extend to lower stellar masses, and the hosts of nonrepeaters arise in more optically luminous galaxies. While four of the galaxies with the clearest and most prolonged rises in their SFHs all host repeating FRBs, demonstrating heightened star formation activity in the last ≲100 Myr, one nonrepeating host shows this SFH as well. Our results support progenitor models with short delay channels (i.e., magnetars formed via core-collapse supernova) for most FRBs, but the presence of some FRBs in less-active environments suggests a fraction form through more delayed channels.
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: American Association for the Advancement of Science (AAAS)
Date: 09-08-2019
Abstract: Fast radio bursts (FRBs) are brief radio emissions from distant astronomical sources. Some are known to repeat, but most are single bursts. Nonrepeating FRB observations have had insufficient positional accuracy to localize them to an in idual host galaxy. We report the interferometric localization of the single-pulse FRB 180924 to a position 4 kiloparsecs from the center of a luminous galaxy at redshift 0.3214. The burst has not been observed to repeat. The properties of the burst and its host are markedly different from those of the only other accurately localized FRB source. The integrated electron column density along the line of sight closely matches models of the intergalactic medium, indicating that some FRBs are clean probes of the baryonic component of the cosmic web.
Publisher: Oxford University Press (OUP)
Date: 03-02-2023
Abstract: We present new upgraded Giant Metrewave Radio Telescope H i 21-cm observations of the ultra-luminous infrared galaxy IRAS 10565 + 2448, previously reported to show blueshifted, broad, and shallow H i absorption indicating an outflow. Our higher spatial resolution observations have localized this blueshifted outflow, which is ∼ 1.36 kpc southwest of the radio centre and has a blueshifted velocity of $\\sim 148\\, \\rm km\\, s^{-1}$ and a full width at half maximum of $\\sim 581\\, \\rm km\\, s^{-1}$. The spatial extent and kinematic properties of the H i outflow are consistent with the previously detected cold molecular outflows in IRAS 10565 + 2448, suggesting that they likely have the same driving mechanism and are tracing the same outflow. By combining the multiphase gas observations, we estimate a total outflowing mass rate of at least $140\\, \\rm M_\\odot \\, yr^{-1}$ and a total energy loss rate of at least $8.9\\times 10^{42}\\, \\rm erg\\, s^{-1}$, where the contribution from the ionized outflow is negligible, emphasizing the importance of including both cold neutral and molecular gas when quantifying the impact of outflows. We present evidence of the presence of a radio jet and argue that this may play a role in driving the observed outflows. The modest radio luminosity $L_{\\rm 1.4GHz}\\, \\sim 1.3\\times 10^{23}\\, {\\rm W\\, Hz^{-1}}$ of the jet in IRAS 10565 + 2448 implies that the jet contribution to driving outflows should not be ignored in low radio luminosity active galactic nuclei.
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.27
Abstract: The putative host galaxy of FRB 20171020A was first identified as ESO 601-G036 in 2018, but as no repeat bursts have been detected, direct confirmation of the host remains elusive. In light of recent developments in the field, we re-examine this host and determine a new association confidence level of 98%. At 37 Mpc, this makes ESO 601-G036 the third closest FRB host galaxy to be identified to date and the closest to host an apparently non-repeating FRB (with an estimated repetition rate limit of $ $ $0.011$ bursts per day above $10^{39}$ erg). Due to its close distance, we are able to perform detailed multi-wavelength analysis on the ESO 601-G036 system. Follow-up observations confirm ESO 601-G036 to be a typical star-forming galaxy with H i and stellar masses of $\\log_{10}\\!(M_{\\rm{H\\,{\\small I}}} / M_\\odot) \\sim 9.2$ and $\\log_{10}\\!(M_\\star / M_\\odot) = 8.64^{+0.03}_{-0.15}$ , and a star formation rate of $\\text{SFR} = 0.09 \\pm 0.01\\,{\\rm M}_\\odot\\,\\text{yr}^{-1}$ . We detect, for the first time, a diffuse gaseous tail ( $\\log_{10}\\!(M_{\\rm{H\\,{\\small I}}} / M_\\odot) \\sim 8.3$ ) extending to the south-west that suggests recent interactions, likely with the confirmed nearby companion ESO 601-G037. ESO 601-G037 is a stellar shred located to the south of ESO 601-G036 that has an arc-like morphology, is about an order of magnitude less massive, and has a lower gas metallicity that is indicative of a younger stellar population. The properties of the ESO 601-G036 system indicate an ongoing minor merger event, which is affecting the overall gaseous component of the system and the stars within ESO 601-G037. Such activity is consistent with current FRB progenitor models involving magnetars and the signs of recent interactions in other nearby FRB host galaxies.
Publisher: EDP Sciences
Date: 22-06-2015
Publisher: EDP Sciences
Date: 09-2018
DOI: 10.1051/0004-6361/201833108
Abstract: The energetic feedback that is generated by radio jets in active galactic nuclei (AGNs) has been suggested to be able to produce fast outflows of atomic hydrogen (H I ) gas, which can be studied in absorption at high spatial resolution. We have used the Very Large Array (VLA) and a global very long baseline interferometry (VLBI) array to locate and study in detail the H I outflow discovered with the Westerbork Synthesis Radio Telescope (WSRT) in the restarted radio galaxy 3C 236. Based on the VLA data, we confirm a blueshifted wing of the H I with a width of ~1000 km s −1 . This H I outflow is partially recovered by the VLBI observation. In particular, we detect four clouds with masses of 0.28 − 1.5 × 10 4 M ⊙ with VLBI that do not follow the regular rotation of most of the H I . Three of these clouds are located, in projection, against the nuclear region on scales of ≲40 pc, while the fourth is cospatial to the southeast lobe at a projected distance of ~270 pc. Their velocities are between 150 and 640 km s −1 blueshifted with respect to the velocity of the disk-related H I . These findings suggest that the outflow is at least partly formed by clouds, as predicted by some numerical simulations, and that it originates already in the inner (few tens of pc) region of the radio galaxy. Our results indicate that the entire outflow might consist of many clouds, possibly with comparable properties as those clearly detected, but distributed at larger radii from the nucleus where the lower brightness of the lobe does not allow us to detect them. However, we cannot rule out a diffuse component of the outflow. Because 3C 236 is a low-excitation radio galaxy, it is less likely that the optical AGN is able to produce strong radiative winds. This leaves the radio jet as the main driver for the H I outflow.
Publisher: American Astronomical Society
Date: 17-01-2022
Abstract: We present the localization and host galaxies of one repeating and two apparently nonrepeating fast radio bursts (FRBs). FRB 20180301A was detected and localized with the Karl G. Jansky Very Large Array to a star-forming galaxy at z = 0.3304. FRB20191228A and FRB20200906A were detected and localized by the Australian Square Kilometre Array Pathfinder to host galaxies at z = 0.2430 and z = 0.3688, respectively. We combine these with 13 other well-localized FRBs in the literature, and analyze the host galaxy properties. We find no significant differences in the host properties of repeating and apparently nonrepeating FRBs. FRB hosts are moderately star forming, with masses slightly offset from the star-forming main sequence. Star formation and low-ionization nuclear emission-line region emission are major sources of ionization in FRB host galaxies, with the former dominant in repeating FRB hosts. FRB hosts do not track stellar mass and star formation as seen in field galaxies (more than 95% confidence). FRBs are rare in massive red galaxies, suggesting that progenitor formation channels are not solely dominated by delayed channels which lag star formation by gigayears. The global properties of FRB hosts are indistinguishable from core-collapse supernovae and short gamma-ray bursts hosts, and the spatial offset (from galaxy centers) of FRBs is mostly inconsistent with that of the Galactic neutron star population (95% confidence). The spatial offsets of FRBs (normalized to the galaxy effective radius) also differ from those of globular clusters in late- and early-type galaxies with 95% confidence.
Publisher: American Astronomical Society
Date: 28-06-2012
Publisher: EDP Sciences
Date: 02-2017
Publisher: Oxford University Press (OUP)
Date: 18-08-2022
Abstract: We present the results of a search for associated 21 cm H i absorption at redshift 0.42 & z & 1.00 in radio-loud galaxies from three Galaxy And Mass Assembly (GAMA) survey fields. These observations were carried out as part of a pilot survey for the Australian SKA Pathfinder (ASKAP) First Large Absorption Survey in H i (FLASH). From a s le of 326 radio sources with 855.5 MHz peak flux density above 10 mJy, we detected two associated H i absorption systems, in SDSS J090331+010847 at z = 0.522 and SDSS J113622+004852 at z = 0.563. Both galaxies are massive (stellar mass $\\gt 10^{11}\\, \\mathrm{M}_\\odot$) and have optical spectra characteristic of luminous red galaxies, though spectral energy distribution fitting implies that SDSS J113622+004852 contains a dust-obscured starburst with star formation rate ∼69 M⊙ yr−1. The H i absorption lines have a high optical depth, with τpk of 1.77 ± 0.16 for SDSS J090331+010847 (the highest value for any z & 0.1 associated system found to date) and 0.14 ± 0.01 for SDSS J113622+004852. In the redshift range probed by our ASKAP observations, the detection rate for associated H i absorption lines (with τpk & 0.1 and at least 3σ significance) is $2.9_{-2.6}^{+9.7}$ per cent. Although the current s le is small, this rate is consistent with a trend seen in other studies for a lower detection rate of associated 21 cm H i absorption systems at higher redshift. We also searched for OH absorption lines at 0.67 & z & 1.34, but no detection was made in the 145 radio sources searched.
Publisher: Wiley
Date: 11-2021
Abstract: GHz‐Peaked Spectrum (GPS) and compact steep spectrum (CSS) sources are thought to represent a young and/or confined sub‐population of radio‐loud active galactic nuclei (AGN) that are yet to evacuate their surrounding ambient interstellar gas. By studying the gaseous environments of these objects, we can gain an insight into the inter‐dependent relationship between galaxies and their supermassive black holes (SMBHs). The First Large Absorption Survey in Hi (FLASH) will build a census of the neutral atomic hydrogen ( Hi ) gas in galaxies at intermediate cosmological redshifts. FLASH is expected to detect at least several hundred Hi absorbers associated with GPS and CSS sources. These absorbers provide an important probe of the abundance and kinematics of line‐of‐sight neutral gas toward radio AGN, in some cases revealing gas associated with infalling clouds and outflows. Observations are now complete for the first phase of the FLASH Pilot Survey and early analysis has already yielded several detections, including the GPS source PKS 2311‐477. Optical imaging of this galaxy reveals an interacting system that could have supplied the neutral gas seen in absorption and triggered the radio‐loud AGN. FLASH will provide a statistically significant s le with which the prevalence of such gas‐rich interactions among compact radio galaxies can be investigated.
Publisher: EDP Sciences
Date: 11-2014
Publisher: EDP Sciences
Date: 30-10-2015
Publisher: Cambridge University Press (CUP)
Date: 08-2009
DOI: 10.1017/S1743921310006411
Abstract: The recently completed AT20G survey provides the largest and most complete s le of high-frequency selected radio sources yet obtained, and offers new insights into the nature of the high-frequency active galaxy population. Here we focus on the optical properties of this survey which highlights the difference of the AT20G source population compared to other radio-selected AGN s les.
Publisher: EDP Sciences
Date: 06-07-2108
Publisher: Oxford University Press (OUP)
Date: 06-07-2017
Publisher: Oxford University Press (OUP)
Date: 11-01-2010
Publisher: Oxford University Press (OUP)
Date: 03-10-2017
Publisher: EDP Sciences
Date: 02-2019
DOI: 10.1051/0004-6361/201833559
Abstract: The LOFAR Two-metre Sky Survey (LoTSS) is an ongoing sensitive, high-resolution 120–168 MHz survey of the entire northern sky for which observations are now 20% complete. We present our first full-quality public data release. For this data release 424 square degrees, or 2% of the eventual coverage, in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45°00′00″ to 57°00′00″) were mapped using a fully automated direction-dependent calibration and imaging pipeline that we developed. A total of 325 694 sources are detected with a signal of at least five times the noise, and the source density is a factor of ∼10 higher than the most sensitive existing very wide-area radio-continuum surveys. The median sensitivity is S 144 MHz = 71 μ Jy beam −1 and the point-source completeness is 90% at an integrated flux density of 0.45 mJy. The resolution of the images is 6″ and the positional accuracy is within 0.2″. This data release consists of a catalogue containing location, flux, and shape estimates together with 58 mosaic images that cover the catalogued area. In this paper we provide an overview of the data release with a focus on the processing of the LOFAR data and the characteristics of the resulting images. In two accompanying papers we provide the radio source associations and deblending and, where possible, the optical identifications of the radio sources together with the photometric redshifts and properties of the host galaxies. These data release papers are published together with a further ∼20 articles that highlight the scientific potential of LoTSS.
Publisher: Oxford University Press (OUP)
Date: 13-08-2013
Publisher: EDP Sciences
Date: 03-2021
DOI: 10.1051/0004-6361/202037677
Abstract: Massive outflows of neutral atomic hydrogen (H I ) have been observed in absorption in a number of radio galaxies and are considered a signature of active galactic nucleus (AGN) feedback. These outflows on kiloparsec scales have not been investigated in great detail as they require high-angular-resolution observations to be spatially resolved. In some radio AGN, they are likely to be the result of the radio jets interacting with the interstellar medium. We have used the global very-long-baseline-interferometry (VLBI) array to map the H I outflow in a small s le of young and restarted radio galaxies that we previously observed with the Very Large Array and the Westerbork Synthesis Radio Telescope at a lower resolution. Here we report on our findings for 4C 52.37 and 3C 293 and we discuss the s le including the previously published 4C 12.50 and 3C 236 . For 4C 52.37 , we present the first ever H I VLBI observations, which recovered the majority of the outflowing H I gas in the form of clouds toward the central 100 pc of the AGN. The clouds are blueshifted by up to ∼600 km s −1 with respect to the systemic velocity. 3C 293 is largely resolved out in our VLBI observation, but toward the VLBI core we detect some outflowing H I gas blueshifted with respect to the systemic velocity by up to ∼300 km s −1 . We also find indications of outflowing gas toward the other parts of the western lobe suggesting that the H I outflow is extended. Overall, we find that the fraction of H I gas recovered by our VLBI observations varies significantly within our s le, ranging from complete ( 4C 12.50 ) to marginal ( 3C 293 ). However, in all cases we find evidence for a clumpy structure of both the outflowing and the quiescent gas, consistent with predictions from numerical simulations. All the outflows include at least a component of relatively compact clouds with masses in the range of 10 4 − 10 5 M ⊙ . The outflowing clouds are often already observed at a few tens of parsecs (in projection) from the core. We find indications that the H I outflow might have a diffuse component, especially in larger sources. Our results support the interpretation that we observe these AGNs at different stages in the evolution of the interaction between the jet and the interstellar medium and this is reflected in the properties of the outflowing gas as predicted by numerical simulations.
Publisher: Oxford University Press (OUP)
Date: 05-2017
Publisher: American Astronomical Society
Date: 06-2020
Publisher: Oxford University Press (OUP)
Date: 04-08-2023
Abstract: FRB 20210912A is a fast radio burst (FRB), detected and localized to subarcsecond precision by the Australian Square Kilometre Array Pathfinder. No host galaxy has been identified for this burst despite the high precision of its localization and deep optical and infrared follow-up, to 5σ limits of R = 26.7 mag and Ks = 24.9 mag with the Very Large Telescope. The combination of precise radio localization and deep optical imaging has almost always resulted in the secure identification of a host galaxy, and this is the first case in which the line of sight is not obscured by the Galactic disc. The dispersion measure of this burst, DMFRB = 1233.696 ± 0.006 pc cm−3, allows for a large source redshift of z & 1 according to the Macquart relation. It could thus be that the host galaxy is consistent with the known population of FRB hosts, but is too distant to detect in our observations (z & 0.7 for a host like that of the first repeating FRB source, FRB 20121102A) that it is more nearby with a significant excess in DMhost, and thus dimmer than any known FRB host or, least likely, that the FRB is truly hostless. We consider each possibility, making use of the population of known FRB hosts to frame each scenario. The fact of the missing host has ramifications for the FRB field: even with high-precision localization and deep follow-up, some FRB hosts may be difficult to detect, with more distant hosts being the less likely to be found. This has implications for FRB cosmology, in which high-redshift detections are valuable.
Publisher: Oxford University Press (OUP)
Date: 21-04-2017
DOI: 10.1093/MNRAS/STX959
Publisher: Oxford University Press (OUP)
Date: 15-07-2019
Abstract: With the Australian Square Kilometre Array Pathfinder (ASKAP) we monitored the black hole candidate X-ray binary MAXI J1535–571 over seven epochs from 2017 September 21 to October 2. Using ASKAP observations, we studied the H i absorption spectrum from gas clouds along the line of sight and thereby constrained the distance to the source. The maximum negative radial velocities measured from the H i absorption spectra for MAXI J1535–571 and an extragalactic source in the same field of view are −69 ± 4 and −89 ± 4 km s−1, respectively. This rules out the far kinematic distance ($9.3^{+0.5}_{-0.6}$ kpc), giving a most likely distance of $4.1^{+0.6}_{-0.5}$ kpc, with a strong upper limit of the tangent point at $6.7^{+0.1}_{-0.2}$ kpc. At our preferred distance, the peak unabsorbed luminosity of MAXI J1535–571 was per cent of the Eddington luminosity, and shows that the soft-to-hard spectral state transition occurred at the very low luminosity of (1.2–3.4) × 10−5 times the Eddington luminosity. Finally, this study highlights the capabilities of new wide-field radio telescopes to probe Galactic transient outbursts, by allowing us to observe both a target source and a background comparison source in a single telescope pointing.
Publisher: Oxford University Press (OUP)
Date: 23-11-2015
Publisher: American Association for the Advancement of Science (AAAS)
Date: 11-10-2019
Abstract: Fast radio bursts (FRBs) are millisecond flashes of radio emission from distant galaxies. It has only recently become possible to locate single bursts precisely enough to determine the host galaxy. Prochaska et al. have observed and localized a FRB using a radio interferometer. The line of sight to the host galaxy coincidentally passes through the outskirts of a closer foreground galaxy. By analyzing the propagation of the FRB, the authors put constraints on the density and magnetization of gas in the outskirts of the foreground galaxy. The technique provides complementary information to existing methods using background quasars. Science , this issue p. 231
Publisher: Cambridge University Press (CUP)
Date: 10-2013
DOI: 10.1017/S1743921314003494
Abstract: We are performing a multi-frequency radio analysis of a well-known deep field: the Lockman Hole, which is one of the best studied sky regions in different wavebands. This will provide us with important complementary data (for ex le redshifts) to the radio data, allowing us to characterize the physical and evolutionary properties of the various classes of sources composing the faint radio population. LOFAR imaging of the Lockman Hole can play an important role in this project, allowing, for the very first time, to observe the sub-mJy source population at very low frequencies (30-200 MHz), where self-absorption phenomena are expected to be very important. Here we present some preliminary results.
Publisher: Oxford University Press (OUP)
Date: 09-04-2020
Abstract: We present early science results from the First Large Absorption Survey in H i (FLASH), a spectroscopically blind survey for 21-cm absorption lines in cold hydrogen (H i) gas at cosmological distances using the Australian Square Kilometre Array Pathfinder (ASKAP). We have searched for H i absorption towards 1253 radio sources in the GAMA 23 field, covering redshifts between z = 0.34 and 0.79 over a sky area of approximately 50 deg2. In a purely blind search, we did not obtain any detections of 21-cm absorbers above our reliability threshold. Assuming a fiducial value for the H i spin temperature of Tspin = 100 K and source covering fraction cf = 1, the total comoving absorption path-length sensitive to all D ed Lyman α Absorbers (DLAs NH i ≥ 2 × 1020 cm−2) is ΔX = 6.6 ± 0.3 (Δz = 3.7 ± 0.2) and super-DLAs (NH i ≥ 2 × 1021 cm−2) is ΔX = 111 ± 6 (Δz= 63 ± 3). We estimate upper limits on the H i column density frequency distribution function that are consistent with measurements from prior surveys for redshifted optical DLAs, and nearby 21-cm emission and absorption. By cross-matching our s le of radio sources with optical spectroscopic identifications of galaxies in the GAMA 23 field, we were able to detect 21-cm absorption at z = 0.3562 towards NVSS J224500−343030, with a column density of $N_{\\rm H\\,\\small{I}} = (1.2 \\pm 0.1) \\times 10^{20}\\, (T_{\\rm spin}/100\\, \\mathrm{K})$ cm−2. The absorber is associated with GAMA J22450.05−343031.7, a massive early-type galaxy at an impact parameter of 17 kpc with respect to the radio source and which may contain a massive (MH i ≳ 3 × 109 M⊙) gas disc. Such gas-rich early types are rare, but have been detected in the nearby Universe.
Publisher: Oxford University Press (OUP)
Date: 10-05-2012
Publisher: EDP Sciences
Date: 10-12-2015
Location: Australia
Start Date: 2018
End Date: 2018
Amount: $336,288.00
Funder: Australian Research Council
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