ORCID Profile
0000-0003-0436-4680
Current Organisations
First Light Fusion Ltd
,
University of Oxford
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Astronomical and Space Sciences | Galactic Astronomy | Cosmology and Extragalactic Astronomy
Publisher: Cambridge University Press (CUP)
Date: 2016
DOI: 10.1017/PASA.2016.37
Abstract: We describe the performance of the Boolardy Engineering Test Array, the prototype for the Australian Square Kilometre Array Pathfinder telescope. Boolardy Engineering Test Array is the first aperture synthesis radio telescope to use phased array feed technology, giving it the ability to electronically form up to nine dual-polarisation beams. We report the methods developed for forming and measuring the beams, and the adaptations that have been made to the traditional calibration and imaging procedures in order to allow BETA to function as a multi-beam aperture synthesis telescope. We describe the commissioning of the instrument and present details of Boolardy Engineering Test Array’s performance: sensitivity, beam characteristics, polarimetric properties, and image quality. We summarise the astronomical science that it has produced and draw lessons from operating Boolardy Engineering Test Array that will be relevant to the commissioning and operation of the final Australian Square Kilometre Array Path telescope.
Publisher: Oxford University Press (OUP)
Date: 09-12-2021
Abstract: We present neutral hydrogen (H i) absorption spectra of the black hole candidate X-ray binary (XRB) MAXI J1348–630 using the Australian Square Kilometre Array Pathfinder (ASKAP) and MeerKAT. The ASKAP H i spectrum shows a maximum negative radial velocity (with respect to the local standard of rest) of −31 ± 4 km s−1 for MAXI J1348–630, as compared to −50 ± 4 km s−1 for a stacked spectrum of several nearby extragalactic sources. This implies a most probable distance of $2.2^{+0.5}_{-0.6}$ kpc for MAXI J1348–630, and a strong upper limit of the tangent point distance at 5.3 ± 0.1 kpc. Our preferred distance implies that MAXI J1348–630 reached 17 ± 10 per cent of the Eddington luminosity at the peak of its outburst, and that the source transited from the soft to the hard X-ray spectral state at 2.5 ± 1.5 per cent of the Eddington luminosity. The MeerKAT H i spectrum of MAXI J1348–630 (obtained from the older, low-resolution 4k mode) is consistent with the re-binned ASKAP spectrum, highlighting the potential of the eventual capabilities of MeerKAT for XRB spectral line studies.
Publisher: Oxford University Press (OUP)
Date: 09-12-2019
Abstract: We present 1–10 GHz radio continuum flux density, spectral index, polarization, and rotation measure (RM) images of the youngest known Galactic supernova remnant (SNR) G1.9+0.3, using observations from the Australia Telescope Compact Array. We have conducted an expansion study spanning eight epochs between 1984 and 2017, yielding results consistent with previous expansion studies of G1.9+0.3. We find a mean radio continuum expansion rate of (0.78 ± 0.09) per cent yr−1 (or ∼8900 km s−1 at an assumed distance of 8.5 kpc), although the expansion rate varies across the SNR perimetre. In the case of the most recent epoch between 2016 and 2017, we observe faster-than-expected expansion of the northern region. We find a global spectral index for G1.9+0.3 of −0.81 ± 0.02 (76 MHz–10 GHz). Towards the northern region, however, the radio spectrum is observed to steepen significantly (∼−1). Towards the two so-called (east and west) ‘ears’ of G1.9+0.3, we find very different RM values of 400–600 and 100–200 rad m2, respectively. The fractional polarization of the radio continuum emission reaches (19 ± 2) per cent, consistent with other, slightly older, SNRs such as Cas A.
Publisher: Oxford University Press (OUP)
Date: 25-10-2021
Abstract: We present results from a search for the H i 21-cm line in absorption towards 16 bright radio sources with the six-antenna commissioning array of the Australian Square Kilometre Array Pathfinder. Our targets were selected from the 2-Jy s le, a flux-limited survey of the southern radio sky with extensive multiwavelength follow-up. Two sources were detected in H i absorption including a new detection towards the bright Fanaroff–Riley Type II radio galaxy PKS 0409−75 at a redshift of $z$ = 0.674. The H i absorption line is blueshifted by ∼3300 km s−1 compared to the optical redshift of the host galaxy of PKS 0409−75 at $z$ = 0.693. Deep optical imaging and spectroscopic follow-up with the GMOS instrument on the Gemini-South telescope reveal that the H i absorption is associated with a galaxy in front of the southern radio lobe with a stellar mass of 3.2–6.8 × 1011 M⊙, a star formation rate of ∼1.24 M⊙ yr−1, and an estimated H i column density of 2.16 × 1021 cm−2, assuming a spin temperature of Tspin = 500 K and source covering factor of Cf = 0.3. Using polarization measurements of PKS 0409−75 from the literature, we estimate the magnetic field of the absorbing galaxy to be ∼14.5 $\\mu$G, consistent with field strengths observed in nearby spiral galaxies but larger than expected for an elliptical galaxy. Results from this pilot study can inform future surveys as new wide-field telescopes allow us to search for 21-cm H i absorption towards all bright radio sources as opposed to smaller targeted s les.
Publisher: Oxford University Press (OUP)
Date: 18-12-2021
Abstract: Determining the spatial distribution and intrinsic physical properties of neutral hydrogen on cosmological scales is one of the key goals of next-generation radio surveys. We use the EAGLE galaxy formation simulations to assess the properties of d ed Lyman α absorbers (DLAs) that are associated with galaxies and their underlying dark matter haloes between 0 ≤ z ≤ 2. We find that the covering fraction of DLAs increases at higher redshift a significant fraction of neutral atomic hydrogen (H i) resides in the outskirts of galaxies with stellar mass ≥1010 M⊙ and the covering fraction of DLAs in the circumgalactic medium (CGM) is enhanced relative to that of the interstellar medium (ISM) with increasing halo mass. Moreover, we find that the mean density of the H i in galaxies increases with increasing stellar mass, while the DLAs in high- and low-halo mass systems have higher column densities than those in galaxies with intermediate halo masses (∼1012 M⊙ at z = 0). These high-impact CGM DLAs in high-stellar mass systems tend to be metal poor, likely tracing smooth accretion. Overall, our results point to the CGM playing an important role in DLA studies at high redshift (z ≥ 1). However, their properties are impacted both by numerical resolution and the detailed feedback prescriptions employed in cosmological simulations, particularly that of active galactic nuclei.
Publisher: Oxford University Press (OUP)
Date: 19-07-2016
Publisher: Oxford University Press (OUP)
Date: 05-10-2016
Publisher: Oxford University Press (OUP)
Date: 10-2020
Abstract: OH absorption is currently the only viable way to detect OH molecules in non-masing galaxies at cosmological distances. There have been only six such detections at z & 0.05 to date and so it is hard to put a statistically robust constraint on OH column densities in distant galaxies. We carried out a pilot OH absorption survey towards eight associated and one intervening H i 21-cm absorbers using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We were able to constrain the OH abundance relative to H i ([OH]/[H i]) to be lower than 10−6 ∼ 10−8 for redshifts z∈ [0.1919, 0.2241]. Although no in idual detection was made, stacking three associated absorbers free of RFI provides a sensitive OH column density 3σ upper-limit $\\sim 1.57 \\times 10^{14} (T_x^{\\rm OH}/10\\,\\mathrm{ K})(1/f_\\mathrm{ c}^{\\rm OH})\\mathrm{ cm}^{-2}$, which corresponds to a [OH]/[H i] & 5.45 × 10−8. Combining with archival data, we show that associated absorbers have a slightly lower OH abundance than intervening absorbers. Our results are consistent with a trend of decreasing OH abundance with decreasing redshift.
Publisher: Oxford University Press (OUP)
Date: 21-09-2019
Abstract: We are just starting to understand the physical processes driving the dramatic change in cosmic star formation rate between z ∼ 2 and the present day. A quantity directly linked to star formation is the molecular gas density, which should be measured through independent methods to explore variations due to cosmic variance and systematic uncertainties. We use intervening CO absorption lines in the spectra of mm-bright background sources to provide a census of the molecular gas mass density of the Universe. The data used in this work are taken from ALMACAL, a wide and deep survey utilizing the ALMA calibrator archive. While we report multiple Galactic absorption lines and one intrinsic absorber, no extragalactic intervening molecular absorbers are detected. However, due to the large redshift path surveyed (Δz = 182), we provide constraints on the molecular column density distribution function beyond z ∼ 0. In addition, we probe column densities of N(H2) 1016 atoms cm−2, 5 orders of magnitude lower than in previous studies. We use the cosmological hydrodynamical simulation IllustrisTNG to show that our upper limits of $\\rho ({\\rm H}_2)\\lesssim 10^{8.3}\\, \\text{M}_{\\odot }\\, \\text{Mpc}^{-3}$ at 0 z ≤ 1.7 already provide new constraints on current theoretical predictions of the cold molecular phase of the gas. These results are in agreement with recent CO emission-line surveys and are complementary to those studies. The combined constraints indicate that the present decrease of the cosmic star formation rate history is consistent with an increasing depletion of molecular gas in galaxies compared to z ∼ 2.
Publisher: Oxford University Press (OUP)
Date: 22-01-2013
DOI: 10.1093/MNRAS/STS678
Publisher: Oxford University Press (OUP)
Date: 21-02-2017
DOI: 10.1093/MNRAS/STX408
Publisher: Oxford University Press (OUP)
Date: 24-10-2019
Publisher: American Association for the Advancement of Science (AAAS)
Date: 22-12-2017
Abstract: The gravitational wave event GW170817 was caused by the merger of two neutron stars (see the Introduction by Smith). In three papers, teams associated with the GROWTH (Global Relay of Observatories Watching Transients Happen) project present their observations of the event at wavelengths from x-rays to radio waves. Evans et al. used space telescopes to detect GW170817 in the ultraviolet and place limits on its x-ray flux, showing that the merger generated a hot explosion known as a blue kilonova. Hallinan et al. describe radio emissions generated as the explosion slammed into the surrounding gas within the host galaxy. Kasliwal et al. present additional observations in the optical and infrared and formulate a model for the event involving a cocoon of material expanding at close to the speed of light, matching the data at all observed wavelengths. Science , this issue p. 1565 , p. 1579 , p. 1559 see also p. 1554
Publisher: Oxford University Press (OUP)
Date: 29-10-2019
Publisher: American Association for the Advancement of Science (AAAS)
Date: 22-12-2017
Abstract: The gravitational wave event GW170817 was caused by the merger of two neutron stars (see the Introduction by Smith). In three papers, teams associated with the GROWTH (Global Relay of Observatories Watching Transients Happen) project present their observations of the event at wavelengths from x-rays to radio waves. Evans et al. used space telescopes to detect GW170817 in the ultraviolet and place limits on its x-ray flux, showing that the merger generated a hot explosion known as a blue kilonova. Hallinan et al. describe radio emissions generated as the explosion slammed into the surrounding gas within the host galaxy. Kasliwal et al. present additional observations in the optical and infrared and formulate a model for the event involving a cocoon of material expanding at close to the speed of light, matching the data at all observed wavelengths. Science , this issue p. 1565 , p. 1579 , p. 1559 see also p. 1554
Publisher: Oxford University Press (OUP)
Date: 21-04-2015
DOI: 10.1093/MNRAS/STV504
Publisher: American Astronomical Society
Date: 22-05-2017
Publisher: Cambridge University Press (CUP)
Date: 08-2012
DOI: 10.1017/S1743921313000926
Abstract: HI absorption-line studies provide a unique probe of the gas distribution and kinematics in galaxies well beyond the local universe ( z ≳ 0.3). HI absorption-line surveys with next-generation radio telescopes will provide the first large-scale studies of HI in a redshift regime which is poorly understood. However, we currently lack the understanding to infer galaxy properties from absorption-line observations alone. To address this issue, we are conducting a search for intervening HI absorption in a s le of 20 nearby galaxies. Our aim is to investigate how the detection rate varies with distance from the galaxy. We target sight-lines to bright continuum sources, which intercept known gas-rich galaxies, selected from the HIPASS Bright Galaxy Catalogue (Koribalski et al. 2004). In our pilot s le, six galaxies with impact parameters 20 kpc, we do not detect any absorption lines — although all are detected in 21cm emission. This indicates that an absorption non-detection cannot simply be interpreted as an absence of neutral gas – see Fig. 1. Our detection rate is low compared to previous surveys e.g. Gupta et al. (2010). This is, at least partially, due to the high resolution of the observations reducing the flux of the background source, which will also be an issue in future surveys, such as ASKAP-FLASH.
Publisher: Oxford University Press (OUP)
Date: 26-02-2016
DOI: 10.1093/MNRAS/STW089
Publisher: Oxford University Press (OUP)
Date: 07-01-2019
DOI: 10.1093/MNRAS/STZ038
Publisher: Oxford University Press (OUP)
Date: 07-11-2016
Publisher: Wiley
Date: 02-2016
Abstract: At present neutral atomic hydrogen (H I ) gas in galaxies at redshifts above z ∼ 0.3 (the extent of 21 cm emission surveys in in idual galaxies) and below z ∼ 1.7 (where the Lyman‐ α line is not observable with ground‐based telescopes) has remained largely unexplored. The advent of precursor telescopes to the Square Kilometre Array will allow us to conduct the first systematic radio‐selected 21 cm absorption surveys for H I over these redshifts. While H I absorption is a tracer of the reservoir of cold neutral gas in galaxies available for star formation, it can also be used to reveal the extreme kinematics associated with jet‐driven neutral outflows in radio‐loud active galactic nuclei. Using the six‐antenna Boolardy Engineering Test Array of the Australian Square Kilometre Array Pathfinder, we have demonstrated that in a single frequency tuning we can detect H I absorption over a broad range of redshifts between z = 0.4 and 1.0. As part of our early science and commissioning program, we are now carrying out a search for absorption towards a s le of the brightest GPS and CSS sources in the southern sky. These intrinsically compact sources present us with an opportunity to study the circumnuclear region of recently re‐started radio galaxies, in some cases showing direct evidence of mechanical feedback through jetdriven outflows. With the sensitivity of the full ASKAP array we will be able to study the kinematics of atomic gas in a few thousand radio galaxies, testing models of radio jet feedback well beyond the nearby Universe. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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: 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: Cambridge University Press (CUP)
Date: 2012
DOI: 10.1071/AS11040
Abstract: The large spectral bandwidth and wide field of view of the Australian SKA Pathfinder radio telescope will open up a completely new parameter space for large extragalactic HI surveys. Here we focus on identifying and parametrising HI absorption lines which occur in the line of sight towards strong radio continuum sources. We have developed a method for simultaneously finding and fitting HI absorption lines in radio data by using multi-nested s ling, a Bayesian Monte Carlo algorithm. The method is tested on a simulated ASKAP data cube, and is shown to be reliable at detecting absorption lines in low signal-to-noise data without the need to smooth or alter the data. Estimation of the local Bayesian evidence statistic provides a quantitative criterion for assigning significance to a detection and selecting between competing analytical line-profile models.
Publisher: Springer Science and Business Media LLC
Date: 10-2018
DOI: 10.1038/S41586-018-0588-Y
Abstract: Despite considerable efforts over the past decade, only 34 fast radio bursts-intense bursts of radio emission from beyond our Galaxy-have been reported
Publisher: Oxford University Press (OUP)
Date: 12-02-2016
Publisher: Oxford University Press (OUP)
Date: 24-09-2022
Abstract: We present radio [1.3 GHz MeerKAT, 4–8 GHz Karl G. Jansky Very Large Array (VLA), and 15.5 GHz Arcminute Microkelvin Imager Large Array (AMI-LA)] and X-ray (Swift and MAXI) data from the 2019 outburst of the candidate Black Hole X-ray Binary (BHXB) EXO 1846−031. We compute a Hardness–Intensity diagram, which shows the characteristic q-shaped hysteresis of BHXBs in outburst. EXO 1846−031 was monitored weekly with MeerKAT and approximately daily with AMI-LA. The VLA observations provide sub-arcsecond-resolution images at key points in the outburst, showing moving radio components. The radio and X-ray light curves broadly follow each other, showing a peak on ∼MJD 58702, followed by a short decline before a second peak between ∼MJD 58731–58739. We estimate the minimum energy of these radio flares from equipartition, calculating values of Emin ∼ 4 × 1041 and 5 × 1042 erg, respectively. The exact date of the return to ‘quiescence’ is missed in the X-ray and radio observations, but we suggest that it likely occurred between MJD 58887 and 58905. From the Swift X-ray flux on MJD 58905 and assuming the soft-to-hard transition happened at 0.3–3 per cent Eddington, we calculate a distance range of 2.4–7.5 kpc. We computed the radio:X-ray plane for EXO 1846−031 in the ‘hard’ state, showing that it is most likely a ‘radio-quiet’ BH, preferentially at 4.5 kpc. Using this distance and a jet inclination angle of θ = 73°, the VLA data place limits on the intrinsic jet speed of βint = 0.29c, indicating subluminal jet motion.
Publisher: Oxford University Press (OUP)
Date: 22-06-2017
Publisher: Wiley
Date: 11-2021
Abstract: Recent studies have shown that both 21 cm HI absorption and soft X‐ray absorption serve as excellent tracers of the dense and dusty gas near the active nucleus of young radio galaxies, offering new insight into the physical nature of the circumnuclear medium. To date, a correlation between the column densities derived using these absorption processes have been observed within Compact Steep Spectrum and Gigahertz‐Peaked Spectrum radio sources. While it is possible that this correlation exists within the broader radio population, many s les of radio galaxies make this difficult to test due to selection effects. This paper explores the possibility of a correlation in the broader radio population by analyzing a historic s le of 168 radio sources compiled from the literature in such a way so as to minimize selection bias. From this historic s le, we conclude that there is some evidence for a correlation between HI and soft X‐ray absorption outside of peaked spectrum sources, but that the selection bias toward these sources makes further analysis difficult using current s les. We discuss this in the context of the SEAFOG project and how forthcoming data will change the landscape of future absorption studies.
Publisher: Oxford University Press (OUP)
Date: 05-09-2019
Abstract: Obscuration of quasars by accreted gas and dust, or dusty intervening galaxies, can cause active galactic nuclei (AGN) to be missed in optically selected surveys. Radio observations can overcome this dust bias. In particular, radio surveys searching for H i absorption inform us on how the AGN can impact on the cold neutral gas medium within the host galaxy, or the population of intervening galaxies through the observed line of sight gas kinematics. We present the results of an H i absorption line survey at 0.4 & z & 1 towards 34 obscured quasars with the Australian SKA Pathfinder (ASKAP) commissioning array. We detect three H i absorption lines, with one of these systems previously unknown. Through optical follow-up for two sources, we find that in all detections the H i gas is associated with the AGN, and hence that these AGN are obscured by material within their host galaxies. Most of our s le are compact, and in addition, are either gigahertz peaked spectrum (GPS), or steep spectrum (CSS) sources, both thought to represent young or recently re-triggered radio AGN. The radio spectral energy distribution classifications for our s le agree with galaxy evolution models in which the obscured AGN has only recently become active. Our associated H i detection rate for GPS and compact SS sources matches those of other surveys towards such sources. We also find shallow and asymmetric H i absorption features, which agrees with previous findings that the cold neutral medium in compact radio galaxies is typically kinematically disturbed by the AGN.
Publisher: Oxford University Press (OUP)
Date: 08-08-2016
Publisher: American Astronomical Society
Date: 16-07-2015
Publisher: American Astronomical Society
Date: 10-2023
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: 31-08-2020
Abstract: We have used the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope to search for intervening 21 cm neutral hydrogen (H i) absorption along the line of sight to 53 bright radio continuum sources. Our observations are sensitive to H i column densities typical of D ed Lyman Alpha absorbers (DLAs) in cool gas with an H i spin temperature below about 300–500 K. The six-dish Boolardy Engineering Test Array (BETA) and twelve-antenna Early Science array (ASKAP-12) covered a frequency range corresponding to redshift 0.4 & z & 1.0 and 0.37 & z & 0.77, respectively, for the H i line. Fifty of the 53 radio sources observed have reliable optical redshifts, giving a total redshift path Δz = 21.37. This was a spectroscopically untargeted survey, with no prior assumptions about the location of the lines in redshift space. Four intervening H i lines were detected, two of them new. In each case, the estimated H i column density lies above the DLA limit for H i spin temperatures above 50–80 K, and we estimate a DLA number density at redshift z ∼ 0.6 of $n(z)=0.19^{+0.15 }_{ -0.09}$. This value lies somewhat above the general trend of n(z) with redshift seen in optical DLA studies. Although the current s le is small, it represents an important proof of concept for the much larger 21 cm First Large Absorption Survey in H i (FLASH) project to be carried out with the full 36-antenna ASKAP telescope, probing a total redshift path $\\Delta z\\sim \\, 50,000$.
Publisher: Oxford University Press (OUP)
Date: 09-04-2015
DOI: 10.1093/MNRAS/STV597
Publisher: Oxford University Press (OUP)
Date: 25-01-2017
DOI: 10.1093/MNRAS/STX214
Publisher: Oxford University Press (OUP)
Date: 29-01-2018
DOI: 10.1093/MNRAS/STY228
Publisher: Oxford University Press (OUP)
Date: 31-12-2016
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: 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: Oxford University Press (OUP)
Date: 24-09-2015
Publisher: Oxford University Press (OUP)
Date: 03-03-2018
Publisher: Springer Science and Business Media LLC
Date: 29-10-2018
Publisher: Oxford University Press (OUP)
Date: 24-08-2015
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: EDP Sciences
Date: 08-2021
DOI: 10.1051/0004-6361/202040232
Abstract: We report a detailed CO(1−0) survey of a galaxy protocluster field at z = 2.16, based on 475 h of observations with the Australia Telescope Compact Array. We constructed a large mosaic of 13 in idual pointings, covering an area of 21 arcmin 2 and ±6500 km s −1 range in velocity. We obtained a robust s le of 46 CO(1−0) detections spanning z = 2.09 − 2.22, constituting the largest s le of molecular gas measurements in protoclusters to date. The CO emitters show an overdensity at z = 2.12 − 2.21, suggesting a galaxy super-protocluster or a protocluster connected to large-scale filaments of ∼120 cMpc in size. We find that 90% of CO emitters have distances .′5−4′ to the center galaxy, indicating that small area surveys would miss the majority of gas reservoirs in similar structures. Half of the CO emitters have velocities larger than escape velocities, which appears gravitationally unbound to the cluster core. These unbound sources are barely found within the R 200 radius around the center, which is consistent with a picture in which the cluster core is collapsed while outer regions are still in formation. Compared to other protoclusters, this structure contains a relatively higher number of CO emitters with relatively narrow line widths and high luminosities, indicating galaxy mergers. We used these CO emitters to place the first constraint on the CO luminosity function and molecular gas density in an overdense environment. The litude of the CO luminosity function is 1.6 ± 0.5 orders of magnitude higher than that observed for field galaxy s les at z ∼ 2, and one order of magnitude higher than predictions for galaxy protoclusters from semi-analytical SHARK models. We derive a high molecular gas density of 0.6 − 1.3 × 10 9 M ⊙ cMpc −3 for this structure, which is consistent with predictions for cold gas density of massive structures from hydro-dynamical DIANOGA simulations.
Publisher: Oxford University Press (OUP)
Date: 06-05-2016
DOI: 10.1093/MNRAS/STW974
Publisher: Oxford University Press (OUP)
Date: 03-2016
DOI: 10.1093/MNRAS/STW186
Publisher: Cambridge University Press (CUP)
Date: 2019
DOI: 10.1017/PASA.2019.16
Abstract: We have observed the G23 field of the Galaxy AndMass Assembly (GAMA) survey using the Australian Square Kilometre Array Pathfinder (ASKAP) in its commissioning phase to validate the performance of the telescope and to characterise the detected galaxy populations. This observation covers ~48 deg 2 with synthesised beam of 32.7 arcsec by 17.8 arcsec at 936MHz, and ~39 deg 2 with synthesised beam of 15.8 arcsec by 12.0 arcsec at 1320MHz. At both frequencies, the root-mean-square (r.m.s.) noise is ~0.1 mJy/beam. We combine these radio observations with the GAMA galaxy data, which includes spectroscopy of galaxies that are i-band selected with a magnitude limit of 19.2. Wide-field Infrared Survey Explorer (WISE) infrared (IR) photometry is used to determine which galaxies host an active galactic nucleus (AGN). In properties including source counts, mass distributions, and IR versus radio luminosity relation, the ASKAP-detected radio sources behave as expected. Radio galaxies have higher stellar mass and luminosity in IR, optical, and UV than other galaxies. We apply optical and IR AGN diagnostics and find that they disagree for ~30% of the galaxies in our s le. We suggest possible causes for the disagreement. Some cases can be explained by optical extinction of the AGN, but for more than half of the cases we do not find a clear explanation. Radio sources aremore likely (~6%) to have an AGN than radio quiet galaxies (~1%), but the majority of AGN are not detected in radio at this sensitivity.
Publisher: Oxford University Press (OUP)
Date: 06-07-2017
Publisher: Oxford University Press (OUP)
Date: 14-01-2016
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.50
Abstract: We present WALLABY pilot data release 1, the first public release of H i pilot survey data from the Wide-field ASKAP L-band Legacy All-sky Blind Survey (WALLABY) on the Australian Square Kilometre Array Pathfinder. Phase 1 of the WALLABY pilot survey targeted three $60\\,\\mathrm{deg}^{2}$ regions on the sky in the direction of the Hydra and Norma galaxy clusters and the NGC 4636 galaxy group, covering the redshift range of $z \\lesssim 0.08$ . The source catalogue, images and spectra of nearly 600 extragalactic H i detections and kinematic models for 109 spatially resolved galaxies are available. As the pilot survey targeted regions containing nearby group and cluster environments, the median redshift of the s le of $z \\approx 0.014$ is relatively low compared to the full WALLABY survey. The median galaxy H i mass is $2.3 \\times 10^{9}\\,{\\rm M}_{{\\odot}}$ . The target noise level of $1.6\\,\\mathrm{mJy}$ per 30 ′′ beam and $18.5\\,\\mathrm{kHz}$ channel translates into a $5 \\sigma$ H i mass sensitivity for point sources of about $5.2 \\times 10^{8} \\, (D_{\\rm L} / \\mathrm{100\\,Mpc})^{2} \\, {\\rm M}_{{\\odot}}$ across 50 spectral channels ( ${\\approx} 200\\,\\mathrm{km \\, s}^{-1}$ ) and a $5 \\sigma$ H i column density sensitivity of about $8.6 \\times 10^{19} \\, (1 + z)^{4}\\,\\mathrm{cm}^{-2}$ across 5 channels ( ${\\approx} 20\\,\\mathrm{km \\, s}^{-1}$ ) for emission filling the 30 ′′ beam. As expected for a pilot survey, several technical issues and artefacts are still affecting the data quality. Most notably, there are systematic flux errors of up to several 10% caused by uncertainties about the exact size and shape of each of the primary beams as well as the presence of sidelobes due to the finite deconvolution threshold. In addition, artefacts such as residual continuum emission and bandpass ripples have affected some of the data. The pilot survey has been highly successful in uncovering such technical problems, most of which are expected to be addressed and rectified before the start of the full WALLABY survey.
Publisher: Oxford University Press (OUP)
Date: 04-04-2013
DOI: 10.1093/MNRAS/STT438
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: Cambridge University Press (CUP)
Date: 2019
DOI: 10.1017/PASA.2019.1
Abstract: The Commensal Real-time Australian Square Kilometre Array Pathfinder Fast Transients survey is the first extensive astronomical survey using phased array feeds. Since January 2017, it has been searching for fast radio bursts in fly’s eye mode. Here, we present a calculation of the sensitivity and total exposure of the survey that detected the first 20 of these bursts, using the pulsars B1641-45 and B0833-45 as calibrators. The beamshape, antenna-dependent system noise, and the effects of radio-frequency interference and fluctuations during commissioning are quantified. Effective survey exposures and sensitivities are calculated as a function of the source counts distribution. Statistical ‘stat’ and systematics ‘sys’ effects are treated separately. The implied fast radio burst rate is significantly lower than the 37 sky −1 day −1 calculated using nominal exposures and sensitivities for this same s le by Shannon et al. (2018). At the Euclidean (best-fit) power-law index of −1.5 (−2.2), the rate is $12.7_{-2.2}^{+3.3}$ (sys) ± 3.6 (stat) sky −1 day −1 ( $20.7_{-1.7}^{+2.1}$ (sys) ± 2.8 (stat) sky −1 day −1 ) above a threshold of 56.6 ± 6.6(sys) Jy ms (40.4 ± 1.2(sys) Jy ms). This strongly suggests that these calculations be performed for other FRB-hunting experiments, allowing meaningful comparisons to be made between them.
Publisher: Oxford University Press (OUP)
Date: 21-04-2016
DOI: 10.1093/MNRAS/STW943
Publisher: Oxford University Press (OUP)
Date: 13-03-2014
DOI: 10.1093/MNRAS/STU289
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: 04-05-2018
Publisher: Oxford University Press (OUP)
Date: 10-05-2012
Publisher: American Association for the Advancement of Science (AAAS)
Date: 02-12-2016
Abstract: The massive Spiderweb galaxy is surrounded by molecular gas as it goes through its formation process.
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.
Publisher: Oxford University Press (OUP)
Date: 12-10-2023
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 11-2010
End Date: 12-2014
Amount: $835,200.00
Funder: Australian Research Council
View Funded Activity