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The distribution of gas and metals in the circumgalactic medium (CGM) plays a critical role in how galaxies evolve. The MUSE-ALMA Haloes survey combines MUSE, ALMA, and HST observations to constrain the properties of the multiphase gas in the CGM and the galaxies associated with the gas probed in absorption. In this paper, we analyse the properties of galaxies associated with 32 strong |${\rm H\, {\small I}}$| Ly-α absorbers at redshift 0.2 ≲ z ≲ 1.4. We detect 79 galaxies within ±500 kms−1 of the absorbers in our 19 MUSE fields. These associated galaxies are found at physical distances from 5.7 kpc and reach star formation rates as low as 0.1 M⊙ yr−1. The significant number of associated galaxies allows us to map their physical distribution on the Δ v and b plane. Building on previous studies, we examine the physical and nebular properties of these associated galaxies and find the following: (i) 27/32 absorbers have galaxy counterparts and more than 50 per cent of the absorbers have two or more associated galaxies, (ii) the |${\rm H\, {\small I}}$| column density of absorbers is anticorrelated with the impact parameter (scaled by virial radius) of the nearest galaxy as expected from simulations, (iii) the metallicity of associated galaxies is typically larger than the absorber metallicity, which decreases at larger impact parameters. It becomes clear that while strong |${\rm H\, {\small I}}$| absorbers are typically associated with more than a single galaxy, we can use them to statistically map the gas and metal distribution in the CGM. [ABSTRACT FROM AUTHOR]

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 sample 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 (W 1− W 2 > 0.5). Therefore, our sample 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 (z median = 0.82), while those dominated by host galaxy colours in mid-infrared have lower redshifts (z median = 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. [ABSTRACT FROM AUTHOR]

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 sample 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 sample 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. [ABSTRACT FROM AUTHOR]

We report the results of a survey for H  i 21-cm absorption at |$z$|  ≲ 0.4 in a new sample of radio sources with the Giant Metrewave Radio Telescope. Of the 11 sources for which there are good data, we obtain zero detections, where four are expected upon accounting for the ionizing photon rates and sensitivity. Adding these to the previously published values, we confirm that the non-detection of 21-cm absorption in active sources at high redshift is due to photo-ionization of the gas rather than excitation by 21-cm photons (significant at 6.09σ and 2.90σ, respectively). We also confirm a strong correlation between the absorption strength and the reddening of the source, suggesting that dust plays a significant role in shielding the gas from the ambient ultraviolet field. An anticorrelation between the 21-cm detection rate and the radio turnover frequency is also found, which runs contrary to what is expected on the basis that the higher the turnover frequency, the more compact the source. It is, however, consistent with the hypothesis that the turnover frequency is related to the electron density, supported by a correlation between the turnover frequency and ionizing photon rate. [ABSTRACT FROM AUTHOR]

Cold neutral gas is a key ingredient for growing the stellar and central black hole mass in galaxies throughout cosmic history. We have used the Atacama Large Millimetre Array to detect a rare example of redshifted 12CO (2–1) absorption in PKS B1740–517, a young (t ∼ 1.6 × 103 yr) and luminous (⁠|$L_{\rm 5\, GHz} \approx 6.6 \times 10^{43}$|  erg s−1) radio galaxy at |$z$|  = 0.44 that is undergoing a tidal interaction with at least one lower mass companion. The coincident H  i 21-cm and molecular absorption have very similar line profiles and reveal a reservoir of cold gas (M gas ∼ 107−108 M⊙), likely distributed in a disc or ring within a few kiloparsecs of the nucleus. A separate H  i component is kinematically distinct and has a very narrow line width (Δ |$v$| FWHM ≲ 5 km s−1), consistent with a single diffuse cloud of cold (T k ∼ 100 K) atomic gas. The 12CO (2–1) absorption is not associated with this component, which suggests that the cloud is either much smaller than 100 pc along our sight line and/or located in low-metallicity gas that was possibly tidally stripped from the companion. We argue that the gas reservoir in PKS B1740–517 may have accreted on to the host galaxy ∼ 50 Myr before the young radio AGN was triggered, but has only recently reached the nucleus. This is consistent with the paradigm that powerful luminous radio galaxies are triggered by minor mergers and interactions with low-mass satellites and represent a brief, possibly recurrent, active phase in the life cycle of massive early-type galaxies. [ABSTRACT FROM AUTHOR]

We report the discovery of an unusual stellar system SMSS J130522.47-293113.0. The optical spectrum is dominated by a blue continuum together with emission lines of hydrogen, neutral, and ionized helium, and the NIII, CIII blend at ~4640-4650 Å. The emission-line profiles vary in strength and position on time-scales as short as 1 d, while optical photometry reveals fluctuations of as much as ~0.2mag in g on time-scales as short as 10-15 min. The system is a weak X-ray source (f0.3-10 = (1.2 ± 0.1) × 10-13 ergs cm2 s-1 in the 0.3-10 keV band) but is not detected at radio wavelengths (3σ upper limit of 50 μJy at 5.5 GHz). The most intriguing property of the system, however, is the existence of two 'blobs', a few arcsec in size, that are symmetrically located 3.'8 (2.2 pc for our preferred system distance of ~2 kpc) each side of the central object. The blobs are detected in optical and near-IR broad-band images but do not show any excess emission in Hα images. We discuss the interpretation of the system, suggesting that the central object is most likely a nova-like CV, and that the blobs are relics of a pc-scale accretion-powered collimated outflow. [ABSTRACT FROM AUTHOR]

We report the first astrophysical application of the technique of wide-field interplanetary scintillation (IPS) with the Murchison Widefield Array (MWA). This powerful technique allows us to identify and measure sub-arcsecond compact components in low-frequency radio sources across large areas of sky without the need for long-baseline interferometry or ionospheric calibration. We present the results of a 5-min observation of a 30 × 30 deg2 MWA field at 162 MHz with 0.5 s time resolution. Of the 2550 continuum sources detected in this field, 302 (12 per cent) show rapid fluctuations caused by IPS. We find that at least 32 per cent of bright low-frequency radio sources contain a sub-arcsecond compact component that contributes over 40 per cent of the total flux density. Perhaps surprisingly, peaked-spectrum radio sources are the dominant population among the strongly scintillating, low-frequency sources in our sample. While gamma-ray active galactic nuclei are generally compact, flat-spectrum radio sources at higher frequencies (162 MHz), the properties of many of the Fermi blazars in our field are consistent with a compact component embedded within more extended low-frequency emission. The detection of a known pulsar in our field shows that the wide-field IPS technique is at the threshold of sensitivity needed to detect new pulsars using image plane analysis, and scaling the current MWA sensitivity to that expected for SKA-low implies that large IPS-based pulsar searches will be feasible with SKA. Calibration strategies for the SKA require a better knowledge of the space density of compact sources at low radio frequencies, which IPS observations can now provide. [ABSTRACT FROM AUTHOR]

Many radio galaxies show the presence of dense and dusty gas near the active nucleus. This can be traced by both 21 cm HI absorption and soft X-ray absorption, offering new insight into the physical nature of the circumnuclear medium of these distant galaxies. To better understand this relationship, we investigate soft X-ray absorption as an indicator for the detection of associated HI absorption, as part of preparation for the First Large Absorption Survey in HI to be undertaken with the Australian Square Kilometre Array Pathfinder (ASKAP). We present the results of our pilot study using the Boolardy Engineering Test Array, a precursor to ASKAP, to search for new absorption detections in radio sources brighter than 1 Jy that also feature soft X-ray absorption. Based on this pilot survey, we detected HI absorption towards the radio source PKS 1657-298 at a redshift of z = 0.42. This source also features the highest X-ray absorption ratio of our pilot sample by a factor of 3, which is consistent with our general findings that X-ray absorption predicates the presence of dense neutral gas. By comparing the X-ray properties of active galactic nuclei with and without detection of HI absorption at radio wavelengths, we find that X-ray hardness ratio and HI absorption optical depth are correlated at a statistical significance of 4.71σ. We conclude by considering the impact of these findings on future radio and X-ray absorption studies. [ABSTRACT FROM AUTHOR]

In this paper, we compare the radio emission at 1.4 GHz with optical outflow signatures of edgeon galaxies. We report observations of six edge-on star-forming galaxies in the Sydney-AAO Multiobject Integral-field spectrograph Galaxy Survey with 1.4 GHz luminosities >1 × 1021 WHz-1. Extended minor axis optical emission is detected with enhanced [N II]/H α line ratios and velocity dispersions consistent with galactic winds in three of six galaxies. These galaxies may host outflows driven by a combination of thermal and cosmic ray processes. We find that galaxies with the strongest wind signatures have extended radio morphologies. Our results form a baseline for understanding the driving mechanisms of galactic winds. [ABSTRACT FROM AUTHOR]

We report the results of a survey for HI 21-cm absorption at redshifts of z ≳ 2.6 in a new sample of radio sources with the Green Bank and Giant Metrewave Radio Telescopes. From a total of 25 targets, we report zero detections in the 16 for which optical depth limits could be obtained. Based upon the detection rate for z ≥ 0.1 associated absorption, we would expect approximately four detections. Of the 11 which have previously not been searched, there is sufficient source-frame optical/ultraviolet photometry to determine the ionizing photon rate for four. Adding these to the literature, the hypothesis that there is a critical rate ofQHI ~ 1056 ionizing photons per second (a monochromatic λ = 912 Å luminosity of LUV ~ 1023 WHz-1) is now significant at ≈7σ. This reaffirms our assertion that searching z ≳ 3 active galaxies for which optical redshifts are available selects sources in which the ultraviolet luminosity is sufficient to ionize all of the neutral gas in the host galaxy. [ABSTRACT FROM AUTHOR]

We study the environments of low- and high-excitation radio galaxies (LERGs and HERGs, respectively) in the redshift range 0.01 < z < 0.4, using a sample of 399 radio galaxies and environmental measurements from the Galaxy And Mass Assembly (GAMA) survey. In our analysis we use the fifth nearest neighbour density (Σ5) and the GAMA galaxy groups catalogue (G3Cv6) and construct control samples of galaxies matched in stellar mass and colour to the radio-detected sample. We find that LERGs and HERGs exist in different environments and that this difference is dependent on radio luminosity. High-luminosity LERGs (LNVSS ≿ 1024 WHz-1) lie in much denser environments than a matched radio-quiet control sample (about three times as dense, as measured by Σ5), and are more likely to be members of galaxy groups (82-5 +7 per cent of LERGs are in GAMA groups, compared to 58-3+3 per cent of the control sample.). In contrast, the environments of the HERGs and lower luminosity LERGs are indistinguishable from that of a matched control sample. Our results imply that high-luminosity LERGs lie in more massive haloes than non-radio galaxies of similar stellar mass and colour, in agreement with earlier studies. When we control for the preference of LERGs to be found in groups, both high- and low-luminosity LERGs are found in higher-mass haloes (~0.2 dex; at least 97 per cent significant) than the non-radio control sample. [ABSTRACT FROM AUTHOR]

H I absorption studies yield information on both active galactic nucleus (AGN) feeding and feedback processes. This AGN activity interacts with the neutral gas in compact radio sources, which are believed to represent the young or recently re-triggered AGN population. We present the results of a survey for H I absorption in a sample of 66 compact radio sources at 0.040 < z < 0.096 with the Australia Telescope Compact Array. In total, we obtained seven detections, five of which are new, with a large range of peak optical depths (3-87 per cent). Of the detections, 71 per cent exhibit asymmetric, broad (ΔvFWHM > 100 km s-1) features, indicative of disturbed gas kinematics. Such broad, shallow and offset features are also found within low-excitation radio galaxies which is attributed to disturbed circumnuclear gas, consistent with early-type galaxies typically devoid of a gas-rich disc. Comparing mid-infrared colours of our galaxies with H I detections indicates that narrow and deep absorption features are preferentially found in late-type and high-excitation radio galaxies in our sample. These features are attributed to gas in galactic discs. By combining XMM-Newton archival data with 21-cm data, we find support that absorbed X-ray sources may be good tracers of H I content within the host galaxy. This sample extends previous H I surveys in compact radio galaxies to lower radio luminosities and provides a basis for future work exploring the higher redshift universe. [ABSTRACT FROM AUTHOR]

Using the Boolardy Engineering Test Array of the Australian Square Kilometre Array Pathfinder (ASKAP BETA), we have carried out the first z = 0-1 survey for H I and OH absorption towards the gravitationally lensed quasars PKS B1830-211 and MG J0414+0534. Although we detected all previously reported intervening systems towards PKS B1830-211, in the case of MG J0414+0534, three systems were not found, indicating that the original identifications may have been confused with radio frequency interference. Given the sensitivity of our data, we find that our detection yield is consistent with the expected frequency of intervening H I systems estimated from previous surveys for 21-cm emission in nearby galaxies and z - 3 damped Lyman α absorbers. We find spectral variability in the z = 0.886 face-on spiral galaxy towards PKS B1830-211 from observations undertaken with the Westerbork Synthesis Radio Telescope in 1997/1998 and ASKAP BETA in 2014/2015. The H I equivalent width varies by a few per cent over approximately yearly time-scales. This long-term spectral variability is correlated between the north-east and south-west images of the core, and with the total flux density of the source, implying that it is observationally coupled to intrinsic changes in the quasar. The absence of any detectable variability in the ratio of H I associated with the two core images is in stark contrast to the behaviour previously seen in the molecular lines. We therefore infer that coherent opaque H I structures in this galaxy are larger than the parsec-scale molecular clouds found at mm-wavelengths. [ABSTRACT FROM AUTHOR]

By combining the data from surveys for H I 21-cm absorption at various impact parameters in near-by galaxies, we report an anti-correlation between the 21-cm absorption strength (velocity integrated optical depth) and the impact parameter. Also, by combining the 21-cm absorption strength with that of the emission, giving the neutral hydrogen column density, NHI, we find no evidence that the spin temperature of the gas (degenerate with the covering factor) varies significantly across the disc. This is consistent with the uniformity of spin temperature measured across the Galactic disc. Furthermore, comparison with the Galactic NHI distribution suggests that intervening 21-cm absorption preferentially arises in discs of high inclinations (near face-on).We also investigate the hypothesis that 21-cm absorption is favourably detected towards compact radio sources. Although there is insufficient data to determine whether there is a higher detection rate towards quasar, rather than radio galaxy, sight-lines, the 21-cm detections intervene objects with a mean turnover frequency of TO>≈ 5 × 108 Hz, compared to TO> ≈ 1 × 108 Hz for the non-detections. Since the turnover frequency is anti-correlated with radio source size, this does indicate a preferential bias for detection towards compact background radio sources. [ABSTRACT FROM AUTHOR]

We present the results of a survey for HI 21 cm and OH 18 cm absorption in seven strong CO emitters at z ≳ 3. Despite reaching limits comparable to those required to detect 21 cm absorption at lower redshifts, we do not detect either transition in any of the objects searched. We believe that this is due to the high-redshift selection causing all of our targets to have ultraviolet (UV) luminosities above the critical value, where all of the atomic gas in the host galaxy disc is suspected to be ionized. However, not only are all of our targets bright in CO emission, but detection of CO above the critical UV luminosity is generally not uncommon. This suggests that the molecular gas is shielded from the radiation or is physically remote from the source of the continuum emission, as it appears to be from CO observations of high-redshift radio galaxies. [ABSTRACT FROM AUTHOR]

We present the results of a survey for intervening 21 cmHI absorption in a sample of 10 nearby, gas-rich galaxies selected from the HI Parkes All-Sky Survey (HIPASS). This follows the six HIPASS galaxies searched in previous work and completes our full sample. In this paper, we searched for absorption along 17 sightlines with impact parameters between 6 and 46 kpc, making one new detection.We also obtained simultaneous HI emission-line data, allowing us to directly relate the absorption-line detection rate to the HI distribution. From this, we find the majority of the non-detections in the current sample are because sightline does not intersect the HI disc of the galaxy at sufficiently high column density, but that source structure is also an important factor. The detected absorption-line arises in the galaxy NGC 5156 (z = 0.01) at an impact parameter of 19 kpc. The line is deep and narrow with an integrated optical depth of 0.82 km s-1. High-resolution Australia Telescope Compact Array (ATCA) images at 5 and 8 GHz reveal that the background source is resolved into two components with a separation of 2.6 arcsec (500 pc at the redshift of the galaxy), with the absorption likely occurring against a single component. We estimate that the ratio of the spin temperature and covering factor, TS/f, is approximately 950 K in the outer disc of NGC 5156, but further observations using very long baseline interferometry would allow us to accurately measure the covering factor and spin temperature of the gas. [ABSTRACT FROM AUTHOR]

Measurement of the evolution of both active galactic nuclei (AGN) and star-formation in galaxies underpins our understanding of galaxy evolution over cosmic time. Radio continuum observations can provide key information on these two processes, in particular via the mechanical feedback produced by radio jets in AGN, and via an unbiased dust-independent measurement of star formation rates. In this paper, we determine radio luminosity functions at 325 MHz for a sample of AGN and star-forming galaxies by matching a 138 deg2 radio survey conducted with the Giant Metrewave Radio Telescope, with optical imaging and redshifts from the Galaxy And Mass Assembly survey. We find that the radio luminosity function at 325 MHz for star-forming galaxies closely follows that measured at 1.4 GHz. By fitting the AGN radio luminosity function out to z = 0.5 as a double power law, and parametrizing the evolution as Φα(1 + z)k, we find evolution parameters of k = 0.92 ± 0.95 assuming pure density evolution and k = 2.13 ± 1.96 assuming pure luminosity evolution. We find that the Low Excitation Radio Galaxies are the dominant population in space density at lower luminosities. Comparing our 325 MHz observations with radio continuum imaging at 1.4 GHz, we determine separate radio luminosity functions for steep- and flat-spectrum AGN, and show that the beamed population of flat-spectrum sources in our sample can be shifted in number density and luminosity to coincide with the unbeamed population of steep-spectrum sources, as is expected in the orientation-based unification of AGN. [ABSTRACT FROM AUTHOR]

We report the discovery of a new 21-cm HI absorption system using commissioning data from the Boolardy Engineering Test Array of the Australian Square Kilometre Array Pathfinder (ASKAP). Using the 711.5-1015.5 MHz band of ASKAP we were able to conduct a blind search for the 21-cm line in a continuous redshift range between z = 0.4 and 1.0, which has, until now, remained largely unexplored. The absorption line is detected at z = 0.44 towards the GHz-peaked spectrum radio source PKS B1740-517 and demonstrates ASKAP's excellent capability for performing a future wide-field survey for HI absorption at these redshifts. Optical spectroscopy and imaging using the Gemini-South telescope indicates that the HI gas is intrinsic to the host galaxy of the radio source. The narrow [OIII] emission lines show clear double-peaked structure, indicating either large-scale outflow or rotation of the ionized gas. Archival data from the XMM-Newton satellite exhibit an absorbed X-ray spectrum that is consistent with a high column density obscuring medium around the active galactic nucleus. The HI absorption profile is complex, with four distinct components ranging in width from 5 to 300 km s-1 and fractional depths from 0.2 to 20 per cent. In addition to systemic HI gas, in a circumnuclear disc or ring structure aligned with the radio jet, we find evidence for a possible broad outflow of neutral gas moving at a radial velocity of v ~ 300 km s-1. We infer that the expanding young radio source (tage 2500 yr) is cocooned within a dense medium and may be driving circumnuclear neutral gas in an outflow of ~1 M⊙ yr-1. [ABSTRACT FROM AUTHOR]

We consider the high radio-frequency (15-353 GHz) properties and variability of 35 brightest cluster galaxies (BCGs). These are the most core-dominated sources drawn from a parent sample of more than 700 X-ray selected clusters, thus allowing us to relate our results to the general population. We find that =6.0 per cent of our parent sample (=15.1 per cent if only cool-core clusters are considered) contain a radio source at 150 GHz of at least 3 mJy (1×1023 W Hz-1 at our median redshift of z 0.13). Furthermore, =3.4 per cent of the BCGs in our parent sample contain a peaked component (Gigahertz Peaked Spectrum, GPS) in their spectra that peaks above 2 GHz, increasing to =8.5 per cent if only cool-core clusters are considered. We see little evidence for strong variability at 15 GHz on short (week-month) time-scales although we see variations greater than 20 per cent at 150 GHz over six-month time frames for 4 of the 23 sources with multi-epoch observations. Much more prevalent is long-term (year-decade time-scale) variability, with average annual amplitude variations greater than 1 per cent at 15 GHz being commonplace. There is a weak trend towards higher variability as the peak of the GPS-like component occurs at higher frequency. We demonstrate the complexity that is seen in the radio spectra of BCGs and discuss the potentially significant implications of these high-peaking components for Sunyaev-Zel'dovich cluster searches. [ABSTRACT FROM AUTHOR]

In the low-redshift Universe, the most powerful radio sources are often associated with gasrich galaxy mergers or interactions. We here present evidence for an advanced, gasich ('wet') merger associated with a powerful radio galaxy at a redshift of z ~ 2. This radio galaxy, MRC 0152-209, is the most infrared-luminous high-redshift radio galaxy known in the Southern hemisphere. Using the Australia Telescope Compact Array, we obtained high-resolution CO(1-0) data of cold molecular gas, which we complement with Hubble Space Telescope (HST)/Wide Field Planetary Camera 2(WFPC2) imaging and William Herschel Telescope long-slit spectroscopy. We find that,while roughly MH2 ~2 x 1010 M⊙ of molecular gas coincides with the central host galaxy, another MH2 ~ 3 x 1010 M⊙ is spread across a total extent of ~60 kpc. Most of this widespread CO(1-0) appears to follow prominent tidal features visible in the rest-frame near-UV HST/WFPC2 imaging. Lya emission shows an excess over He II, but a deficiency over LIR, which is likely the result of photoionization by enhanced but very obscured star formation that was triggered by the merger. In terms of feedback, the radio source is aligned with widespread CO(1-0) emission, which suggests that there is a physical link between the propagating radio jets and the presence of cold molecular gas on scales of the galaxy's halo. Its optical appearance, combined with the transformational stage at which we witness the evolution of MRC 0152-209, leads us to adopt the name 'Dragonfly Galaxy'. [ABSTRACT FROM AUTHOR]

We present the results of a targeted search for intervening HI absorption in six nearby, gas-rich galaxies using the Australia Telescope Compact Array. The sightlines searched have impact parameters of 10-20 kpc. By targeting nearby galaxies, we are also able to map their HI emission, allowing us to directly relate the absorption-line detection rate to the extended HI distribution. The continuum sightlines intersect the HI disc in four of the six galaxies, but no intervening absorption was detected. Of these four galaxies, we find that three of the non-detections are the result of the background source being too faint. In the fourth case, we find that the ratio of the spin temperature to the covering factor (TS/f) must be much higher than expected (≳5700 K) in order to explain the non-detection. We discuss how the structure of the background continuum sources may have affected the detection rate of HI absorption in our sample, and the possible implications for future surveys. Future work including an expanded sample, and very long baseline interferometry observations, would allow us to better investigate the expected detection rate, and influence of background source structure, on the results of future surveys. [ABSTRACT FROM AUTHOR]

We present the results of a targeted search for intervening H I absorption in six nearby, gas-rich galaxies using the Australia Telescope Compact Array. The sightlines searched have impact parameters of 10-20 kpc. By targeting nearby galaxies, we are also able to map their HI emission, allowing us to directly relate the absorption-line detection rate to the extended H I distribution. The continuum sightlines intersect the HI disc in four of the six galaxies, but no intervening absorption was detected. Of these four galaxies, we find that three of the non-detections are the result of the background source being too faint. In the fourth case, we find that the ratio of the spin temperature to the covering factor (T S / f) must be much higher than expected (≳5700 K) in order to explain the non-detection. We discuss how the structure of the background continuum sources may have affected the detection rate of H I absorption in our sample, and the possible implications for future surveys. Future work including an expanded sample, and very long baseline interferometry observations, would allow us to better investigate the expected detection rate, and influence of background source structure, on the results of future surveys. [ABSTRACT FROM AUTHOR]

The lenticular galaxy ESO 243-49 hosts the ultraluminous X-ray source HLX-1, the best candidate intermediate-mass black hole (IMBH) currently known. The environments of IMBHs remain unknown, however, the proposed candidates include the nuclei of dwarf galaxies or globular clusters. Evidence at optical wavelengths points at HLX-1 being the remnant of an accreted dwarf galaxy. Here we report the Australia Telescope Compact Array radio observations of HI emission in and around ESO 243-49 searching for signatures of a recent merger event. No HI line emission is detected in ESO 243-49 with a 5σ upper limit on the HI gas mass of a few 108M⊙ A likely reason for this non-detection is the cluster environment depleting ESO 243-49's HI gas reservoir. The upper limit is consistent with an interpretation of HLX-1 as a dwarf satellite of ESO 243-49, however, more sensitive observations are required for a detection. We detect ~5 x 108M⊙ of HI gas in the peculiar spiral galaxy AM0108-462, located at a projected distance of ~170 kpc from ESO 243-49. This amount of HI gas is ~10 times less than in spiral galaxies with similar optical and near-infrared properties in the field, strengthening the conclusion that the cluster environment indeed depletes the HI gas reservoir of these two galaxies. Here we also report observations of AM 0108-462 in several optical and near-infrared bands using the Magellan 6.5-m telescopes, and archival X-ray and ultraviolet observations with XMM--Newton and Swift. These data combined with the HI line data suggest it is likely that AM 0108-462 is experiencing a merger event. [ABSTRACT FROM AUTHOR]

We present the discovery of a luminous unresolved H II complex on the edge of dwarf galaxy GAMA J141103.98-003242.3 using data from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. This dwarf galaxy is situated at a distance of ∼100 Mpc and contains an unresolved region of H II emission that contributes ∼70 per cent of the galaxy's Hα luminosity, located at the top end of established H II region luminosity functions. For the H II complex, we measure a star formation rate of 0.147 ± 0.041 M⊙ yr-1 and a metal licity of 12+log(O/H) = 8.01 ± 0.05 that is lower than the rest of the galaxy by ∼0.2 dex. Data from the H I Parkes All-Sky Survey (HIPASS) indicate the likely presence of neutral hydrogen in the galaxy to potentially fuel ongoing and future star-forming events. We discuss various triggering mechanisms for the intense star formation activity of this H II complex, where the kinematics of the ionized gas are well described by a rotating disc and do not show any features indicative of interactions. We show that SAMI is an ideal instrument to identify similar systems to GAMA J141103.98-003242.3, and the SAMI Galaxy Survey is likely to find many more of these systems to aid in the understanding of their formation and evolution. [ABSTRACT FROM AUTHOR]

Existing studies of the atomic hydrogen gas content in distant galaxies, through the absorption of the 21-cm line, often infer that the total column density, $N_{{\rm H}\small {I}}$, is anticorrelated with the linear extent of the background radio source, dem. We investigate this interpretation, by dissecting the various parameters from which $N_{{{\rm H}}\,\small {I}}$ is derived, and find that the relationship is driven primarily by the observed optical depth, τobs, which, for a given absorber size, is anticorrelated with dem. Therefore, the inferred $N_{{{\rm H}}\,\small {I}}{\rm -}d_{\rm em}$ anticorrelation is merely the consequence of geometry, in conjunction with the assumption of a common spin temperature/covering factor ratio for each member of the sample, an assumption for which there is scant observational justification. While geometry can explain the observed correlation, many radio sources comprise two radio lobes and so we model the projected area of a two-component emitter intercepted by a foreground absorber. From this, the observed τobs-dem relationship is best reproduced through models which approximate either of the two Fanaroff & Riley classifications, although the observed scatter in the sample cannot be duplicated using a single deprojected radio source size. Furthermore, the trend is best reproduced using an absorber of diameter ∼ 100-1000 pc, which is also the range of values of dem at which the 21-cm detection rate peaks. This may indicate that this is the characteristic linear size of the absorbing gas structure. [ABSTRACT FROM AUTHOR]

We cross-matched the 6-year Swift/Burst Alert Telescope (BAT) survey of active galactic nuclei (AGN) with the AT20G radio survey of the southern sky, which is one of the largest high-frequency radio surveys available. With these data we investigated the possible correlation between the radio and the X-ray emission at the highest radio and X-ray frequencies. We found 37 AGN with a high probability of association (>80 per cent), among which 19 are local Seyfert galaxies (with median redshift z = 0.03) and 18 blazars. We found that ≈20 per cent of the AGN detected in hard X-rays are also bright radio sources at 20 GHz, but the apparent correlation between the radio and hard X-ray luminosity is completely driven by the different median redshifts of the two subgroups of AGN. When we consider only the local Seyfert sample we find no evidence of a correlation between their 20 GHz and 15–55 keV power. Therefore it appears that at high frequencies the radio–X connection, which had been previously observed at lower frequencies, disappears. The disappearance of the radio–X correlation at high radio and X-ray frequencies could be tested through Very Long Baseline Interferometry and the use of the Nuclear Spectroscopic Telescope Array (NuSTAR) satellite. [ABSTRACT FROM AUTHOR]

The high-redshift radio galaxy MRC 1138-262 ('Spiderweb Galaxy'; z = 2.16) is one of the most massive systems in the early Universe and surrounded by a dense 'web' of proto-cluster galaxies. Using the Australia Telescope Compact Array, we detected CO(1-0) emission from cold molecular gas - the raw ingredient for star formation - across the Spiderweb Galaxy. We infer a molecular gas mass of MH2 = 6 x 1010 M&#664- (for MH2/L'CO = 0.8). While the bulk of the molecular gas coincides with the central radio galaxy, there are indications that a substantial fraction of this gas is associated with satellite galaxies or spread across the intergalactic medium on scales of tens of kpc. In addition, we tentatively detect CO(1-0) in the star-forming proto-cluster galaxy HAE 229, 250 kpc to the West. Our observations are consistent with the fact that the Spiderweb Galaxy is building up its stellar mass through a massive burst of widespread star formation. At maximum star formation efficiency, the molecular gas will be able to sustain the current star formation rate (SFR ≈ 1400 M&#664- yr-1, as traced by Seymour et al.) for about 40 Myr. This is similar to the estimated typical lifetime of a major starburst event in infrared luminous merger systems. [ABSTRACT FROM AUTHOR]

We report conclusive verification of the detection of associated H i 21 cm absorption in the early-type host galaxy of the compact radio source PMN J2054−4242. We estimate an effective spectral line velocity width of 418 ± 20 km s−1 and observed peak optical depth of 2.5 ± 0.2 per cent, making this one of the broadest and weakest 21 cm absorption lines yet detected. For Tspin/f > 100 K the atomic neutral hydrogen column density is $N_\mathrm{H\,{\small I}} \gtrsim 2 \times 10^{21}$ cm−2. The observed spectral line profile is redshifted by 187 ± 46 km s−1, with respect to the optical spectroscopic measurement, perhaps indicating that the H i gas is infalling towards the central active galactic nucleus. Our initial tentative detection would likely have been dismissed by visual inspection, and hence its verification here is an excellent test of our spectral line detection technique, currently under development in anticipation of future next-generation 21 cm absorption-line surveys. [ABSTRACT FROM AUTHOR]

We have undertaken a survey for H i 21-cm absorption within the host galaxies of z ∼ 1.2-1.5 radio sources, in the search of the cool neutral gas currently ‘missing’ at z ≳ 1. This deficit is believed to be due to the optical selection of high-redshift objects biasing surveys towards sources of sufficient ultraviolet luminosity to ionize all of the gas in the surrounding galaxy. In order to avoid this bias, we have selected objects above blue magnitudes of B ∼ 20, indicating ultraviolet luminosities below the critical value of LUV ∼ 1023 W Hz−1, above which 21-cm has never been detected. As a secondary requirement to the radio flux and faint optical magnitude, we shortlist targets with radio spectra suggestive of compact sources, in order to maximize the coverage of background emission. From this, we obtain one detection out of 10 sources searched, which at z = 1.278 is the third highest redshift detection of associated 21-cm absorption to date. Accounting for the spectra compromised by radio frequency interference, as well as various other possible pitfalls (reliable optical redshifts and turnover frequencies indicative of compact emission), we estimate a detection rate of ≈30 per cent, close to that expected for LUV ≲ 1023 W Hz−1 sources. [ABSTRACT FROM AUTHOR]

We have constructed a sample of radio-loud objects with optical spectroscopy from the Galaxy and Mass Assembly (GAMA) project over the Herschel Astrophysical Terahertz Large Area Survey (Herschel-ATLAS) Phase 1 fields. Classifying the radio sources in terms of their optical spectra, we find that strong-emission-line sources (‘high-excitation radio galaxies’) have, on average, a factor of ∼4 higher 250-μm Herschel luminosity than weak-line (‘low-excitation’) radio galaxies and are also more luminous than magnitude-matched radio-quiet galaxies at the same redshift. Using all five H-ATLAS bands, we show that this difference in luminosity between the emission-line classes arises mostly from a difference in the average dust temperature; strong-emission-line sources tend to have comparable dust masses to, but higher dust temperatures than, radio galaxies with weak emission lines. We interpret this as showing that radio galaxies with strong nuclear emission lines are much more likely to be associated with star formation in their host galaxy, although there is certainly not a one-to-one relationship between star formation and strong-line active galactic nuclei (AGN) activity. The strong-line sources are estimated to have star formation rates at least a factor of 3–4 higher than those in the weak-line objects. Our conclusion is consistent with earlier work, generally carried out using much smaller samples, and reinforces the general picture of high-excitation radio galaxies as being located in lower-mass, less evolved host galaxies than their low-excitation counterparts. [ABSTRACT FROM PUBLISHER]

ABSTRACT We present results from a search for 21 cm associated H i absorption in a sample of 29 radio sources selected from the Australia Telescope 20 GHz survey. Observations were conducted using the Australia Telescope Compact Array Broadband Backend, with which we can simultaneously look for 21 cm absorption in a redshift range of 0.04 ≲ z≲ 0.08, with a velocity resolution of 7 km s−1. In preparation for future large-scale H i absorption surveys we test a spectral-line finding method based on Bayesian inference. We use this to assign significance to our detections and to determine the best-fitting number of spectral-line components. We find that the automated spectral-line search is limited by residuals in the continuum, both from the band-pass calibration and spectral-ripple subtraction, at spectral-line widths of Δ vFWHM≳ 103 km s−1. Using this technique we detect two new absorbers and a third, previously known, yielding a 10 per cent detection rate. Of the detections, the spectral-line profiles are consistent with the theory that we are seeing different orientations of the absorbing gas, in both the host galaxy and circumnuclear disc, with respect to our line of sight to the source. In order to spatially resolve the spectral-line components in the two new detections, and so verify this conclusion, we require further high-resolution 21 cm observations (∼0.01 arcsec) using very long baseline interferometry. [ABSTRACT FROM AUTHOR]

ABSTRACT Spectral index has been traditionally used to separate extragalactic radio sources into compact and extended populations, with the spectral transition placed variably between −0.4 and −0.6. We use high angular resolution data, measured from visibility of sources at the longest baseline of 4500 m of the Australia Telescope Compact Array (ATCA), for the Australia Telescope 20 GHz (AT20G) survey to obtain angular size information for over 94 per cent of AT20G sources. We confirm the previous AT20G result that due to the high survey frequency of 20 GHz, the source population is strongly dominated by compact sources (79 per cent). At 0.15-arcsec angular resolution limit, we show a very strong correlation between the compact and extended sources with flat and steep-spectrum sources respectively for spectral indices obtained between 1 and 5 GHz. Thus, we provide a firm physical basis for the traditional spectral classification into flat and steep-spectrum sources to select compact and extended sources. We find that for spectral indices between 1 and 5 GHz, the cut-offs at −0.4 and −0.5 are quite similar to the optimum cut-off of −0.46 and, hence, recommend the continued use of −0.5 for future studies. We use the recently published redshift data to study the effect of spectral curvature on the redshift cut-off of compact active galactic nuclei (AGNs). Using spectral indices at different frequencies, we correct for the redshift effect and also produce rest-frame frequency spectra for compact sources for redshifts up to z∼ 5. We show that the spectra of most compact sources are flat to ∼30 GHz and then start to steepen. At higher frequencies, the spectra of both compact and extended sources are steep, so the use of spectral index does not separate the compact and extended source populations as well as in lower frequencies. We also find that due to spectral steepening at high frequencies, surveys of compact sources at higher frequencies (ν > 5 GHz) will have redshift cut-off due to spectral curvature but at frequencies below a few gigahertz, the surveys are not significantly affected by spectral curvature and, thus, the evidence for a strong redshift cut-off in AGNs found in lower frequency surveys is a real cut-off and not a result of K-correction. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a source catalogue of 9040 radio sources resulting from high-resolution observations of 8385 Parkes-MIT-NRAO (PMN) sources with the Australia Telescope Compact Array. The catalogue lists flux density and structural measurements at 4.8 and 8.6 GHz, derived from observations of all PMN sources in the declination range −87° < δ < −385 (exclusive of Galactic latitudes | b| < 2°) with flux density S4850≥ 70 mJy (50 mJy south of δ=−73°). We assess the quality of the data, which were gathered in 1992-1994, describe the population of catalogued sources and compare it to samples from complementary catalogues. In particular we find 127 radio sources with probable association with γ-ray sources observed by the orbiting Fermi Large Area Telescope. [ABSTRACT FROM AUTHOR]

BSTRACT The stellar initial mass function (IMF) describes the distribution in stellar masses produced from a burst of star formation. For more than 50 yr, the implicit assumption underpinning most areas of research involving the IMF has been that it is universal, regardless of time and environment. We measure the high-mass IMF slope for a sample of low-to-moderate redshift galaxies from the Galaxy and Mass Assembly survey. The large range in luminosities and galaxy masses of the sample permits the exploration of underlying IMF dependencies. A strong IMF-star formation rate dependency is discovered, which shows that highly star-forming galaxies form proportionally more massive stars (they have IMFs with flatter power-law slopes) than galaxies with low star formation rates. This has a significant impact on a wide variety of galaxy evolution studies, all of which rely on assumptions about the slope of the IMF. Our result is supported by, and provides an explanation for, the results of numerous recent explorations suggesting a variation of or evolution in the IMF. [ABSTRACT FROM AUTHOR]

BSTRACT We use multiwavelength data from the Galaxy And Mass Assembly (GAMA) and Herschel-ATLAS (H-ATLAS) surveys to compare the relationship between various dust obscuration measures in galaxies. We explore the connections between the ultraviolet (UV) spectral slope, β, the Balmer decrement and the far-infrared (FIR) to 150 nm far-ultraviolet (FUV) luminosity ratio. We explore trends with galaxy mass, star formation rate (SFR) and redshift in order to identify possible systematics in these various measures. We reiterate the finding of other authors that there is a large scatter between the Balmer decrement and the β parameter, and that β may be poorly constrained when derived from only two broad passbands in the UV. We also emphasize that FUV-derived SFRs, corrected for dust obscuration using β, will be overestimated unless a modified relation between β and the attenuation factor is used. Even in the optimum case, the resulting SFRs have a significant scatter, well over an order of magnitude. While there is a stronger correlation between the IR-to-FUV luminosity ratio and β parameter than with the Balmer decrement, neither of these correlations are particularly tight, and dust corrections based on β for high-redshift galaxy SFRs must be treated with caution. We conclude with a description of the extent to which the different obscuration measures are consistent with each other as well as the effects of including other galactic properties on these correlations. [ABSTRACT FROM AUTHOR]

BSTRACT [ABSTRACT FROM AUTHOR]

We present self-consistent star formation rates derived through pan-spectral analysis of galaxies drawn from the Galaxy and Mass Assembly (GAMA) survey. We determine the most appropriate form of dust obscuration correction via application of a range of extinction laws drawn from the literature as applied to Hα, [O ] and UV luminosities. These corrections are applied to a sample of 31 508 galaxies from the GAMA survey at . We consider several different obscuration curves, including those of Milky Way, Calzetti and Fischera & Dopita curves and their effects on the observed luminosities. At the core of this technique is the observed Balmer decrement, and we provide a prescription to apply optimal obscuration corrections using the Balmer decrement. We carry out an analysis of the star formation history (SFH) using stellar population synthesis tools to investigate the evolutionary history of our sample of galaxies as well as to understand the effects of variation in the initial mass function (IMF) and the effects this has on the evolutionary history of galaxies. We find that the Fischera & Dopita obscuration curve with an value of 4.5 gives the best agreement between the different SFR indicators. The 2200 Å feature needed to be removed from this curve to obtain complete consistency between all SFR indicators suggesting that this feature may not be common in the average integrated attenuation of galaxy emission. We also find that the UV dust obscuration is strongly dependent on the SFR. [ABSTRACT FROM AUTHOR]

We present a radio survey carried out with the Australia Telescope Compact Array. A motivation for the survey was to make a complete inventory of the diffuse emission components as a step towards a study of the cosmic evolution in radio source structure and the contribution from radio-mode feedback on galaxy evolution. The Australia Telescope Low-Brightness Survey (ATLBS) at 1388 MHz covers 8.42 deg2 of the sky in an observing mode designed to yield images with exceptional surface brightness sensitivity and low confusion. The survey was carried out in two adjacent regions on the sky centred at RA: , Dec.: and RA: , Dec.: (J2000.0). The ATLBS radio images, made with 0.08 mJy beam−1 rms noise and 50 arcsec beam, detect a total of 1094 sources with peak flux exceeding 0.4 mJy beam−1. The ATLBS source counts were corrected for blending, noise bias, resolution and primary beam attenuation; the normalized differential source counts are consistent with no upturn down to 0.6 mJy. The percentage integrated polarization was computed after corrections for the polarization bias in integrated polarized intensity; shows an increasing trend with decreasing flux density. Simultaneous visibility measurements made with longer baselines yielded images, with 5 arcsec beam, of compact components in sources detected in the survey. The observations provide a measurement of the complexity and diffuse emission associated with mJy and sub-mJy radio sources. 10 per cent of the ATLBS sources have more than half of their flux density in extended emission and the fractional flux in diffuse components does not appear to vary with flux density, although the percentage of sources that have complex structure increases with flux density. The observations are consistent with a transition in the nature of extended radio sources from FR-ii radio source morphology, which dominates the mJy population, to FR-i structure at sub-mJy flux density. [ABSTRACT FROM AUTHOR]

We present the wide-field imaging and polarimetry at of seven most extended, bright , high-frequency selected radio sources in the southern sky with declinations . Accompanying the data are brief reviews of the literature for each source. The results presented here aid in the statistical completeness of the Australia Telescope 20-GHz Survey: the Bright Source Sample. The data are of crucial interest for future cosmic microwave background missions as a collection of information about candidate calibrator sources. We were able to obtain data for seven of the nine sources identified by our selection criteria. We report that Pictor A is thus far the best extragalactic calibrator candidate for the Low Frequency Instrument of the Planck European Space Agency mission due to its high level of integrated polarized flux density on a scale of 10 arcmin. Six out of the seven sources have a clearly detected compact radio core in our images, with either a null detection or less than 2 per cent detection of polarized emission from the nuclei. Most sources with detected jets have magnetic field alignments running in a longitudinal configuration, however, PKS 1333−33 exhibits transverse fields and an orthogonal change in field geometry from nucleus to jets. [ABSTRACT FROM AUTHOR]

Objective To explore physiotherapists' perceptions of mechanisms to explain observed variation in early postoperative practice after hip fracture surgery demonstrated in a national audit. Methods A qualitative semi-structured interview study of 21 physiotherapists working on orthopaedic wards at 7 hospitals with different durations of physiotherapy during a recent audit. Thematic analysis of interviews drawing on Normalisation Process Theory to aid interpretation of findings. Results Four themes were identified: achieving protocolised and personalised care; patient and carer engagement; multidisciplinary team engagement across the care continuum; and strategies for service improvement. Most expressed variation from protocol was legitimate when driven by what is deemed clinically appropriate for a given patient. This tailored approach was deemed essential to optimise patient and carer engagement. Participants reported inconsistent degrees of engagement from the multidisciplinary team attributing this to competing workload priorities, interpreting 'postoperative physiotherapy' as a single professional activity rather than a care delivery approach, plus lack of integration between hospital and community care. All participants recognised changes needed at both structural and process levels to improve their services. Conclusion Physiotherapists highlighted an inherent conflict between their intention to deliver protocolised care while allowing for an individual patient-tailored approach. This conflict has implications for how audit results should be interpreted, how future clinical guidelines are written, and how physiotherapists are trained. Physiotherapists also described additional factors explaining variation in practice which may be addressed through increased engagement of the multidisciplinary team and resources for additional staffing and advanced clinical roles. [ABSTRACT FROM AUTHOR]

We present the detection of an enormous disc of cool neutral hydrogen (H i) gas surrounding the S0 galaxy NGC 612, which hosts one of the nearest powerful radio sources (PKS 0131−36). Using the Australia Telescope Compact Array, we detect of H i emission-line gas that is distributed in a 140-kpc wide disc-like structure along the optical disc and dust lane of NGC 612. The bulk of the gas in the disc appears to be settled in regular rotation with a total velocity range of 850 km s−1, although asymmetries in this disc indicate that perturbations are being exerted on part of the gas, possibly by a number of nearby companions. The H i disc in NGC 612 suggests that the total mass enclosed by the system is , implying that this early-type galaxy contains a massive dark matter halo. We also discuss an earlier study by Holt et al. that revealed the presence of a prominent young stellar population at various locations throughout the disc of NGC 612, indicating that this is a rare example of an extended radio source that is hosted by a galaxy with a large-scale star-forming disc. In addition, we map a faint H i bridge along a distance of 400 kpc in between NGC 612 and the gas-rich barred galaxy NGC 619, indicating that likely an interaction between both systems occurred. From the unusual amounts of H i gas and young stars in this early-type galaxy, in combination with the detection of a faint optical shell and the system's high infrared luminosity, we argue that either ongoing or past galaxy interactions or a major merger event are a likely mechanism for the triggering of the radio source in NGC 612. This paper is part of an ongoing study to map the large-scale neutral hydrogen properties of nearby radio galaxies and it presents the first example of large-scale H i detected around a powerful Fanaroff–Riley type II (FR-II) radio galaxy. The H i properties of the FR-II radio galaxy NGC 612 are very similar to those found for low-power compact radio sources, but different from those of extended Fanaroff–Riley type I (FR-I) sources. [ABSTRACT FROM AUTHOR]

This paper introduces a new program to find high-redshift radio galaxies in the Southern hemisphere through ultrasteep spectrum (USS) selection. We define a sample of 234 USS radio sources with spectral indices α843408≤−1.0 ( Sν∝να) and flux densities S408≥ 200 mJy in a region of 0.35 sr, chosen by cross-correlating the revised 408 MHz Molonglo Reference Catalogue, the 843 MHz Sydney University Molonglo Sky Survey and the 1400 MHz NRAO VLA Sky Survey in the overlap region −40° < δ < −30°. We present Australia Telescope Compact Array (ATCA) high-resolution 1384 and 2368 MHz radio data for each source, which we use to analyse the morphological, spectral index and polarization properties of our sample. We find that 85 per cent of the sources have observed-frame spectral energy distributions that are straight over the frequency range 408–2368 MHz, and that, on average, sources with smaller angular sizes have slightly steeper spectral indices and lower fractional linear polarization. Fractional polarization is anticorrelated with flux density at both 1400 and 2368 MHz. We also use the ATCA data to determine observed-frame Faraday rotation measures for half of the sample. [ABSTRACT FROM AUTHOR]

We report on our further analysis of the expanded and revised sample of potential BL Lac objects (the 2BL) optically identified from two catalogues of blue-selected (UV excess) point sources, the 2-degree field (2dF) and 6-degree field (6dF) quasi-stellar object (QSO) Redshift Surveys (2QZ and 6QZ). The 2BL comprises 52 objects with no apparent proper motion, over the magnitude range . Follow-up high signal-to-noise spectra of 36 2BL objects and near-infrared (NIR) imaging of 18 objects, together with data for 19 2BL objects found in the Sloan Digital Sky Survey (SDSS), show 17 objects to be stellar, while a further 16 objects have evidence of weak, broad emission features, although for at least one of these the continuum level has clearly varied. Classification of three objects remains uncertain, with NIR results indicating a marked reduction in flux as compared to SDSS optical magnitudes. Seven objects have neither high signal-to-noise spectra nor NIR imaging. Deep radio observations of 26 2BL objects at the Very Large Array (VLA) resulted in only three further radio detections; however none of the three is classed as a featureless continuum object. Seven 2BL objects with a radio detection are confirmed as candidate BL Lac objects, while one extragalactic continuum object is undetected at radio frequencies. One further radio-undetected object is also a potential BL Lac candidate. However, it would appear that there is no significant population of radio-quiet BL Lac objects. [ABSTRACT FROM AUTHOR]

We presentBVRIKimages and spectroscopic observations of thehost galaxy of the compact steep-spectrum (CSS) radio source MRC B1221−423. This is a youngradio source with double lobes lying well within the visible galaxy. The host galaxy is undergoing tidal interaction with a nearby companion, with shells, tidal tails and knotty star-forming regions all visible. We analyse the images of the galaxy and its companion pixel-by-pixel, first using colour–magnitude diagrams and then fitting stellar population models to the spectral energy distributions (SEDs) of each pixel. We also present medium-resolution spectroscopy of the system.The pixels separate cleanly in colour–magnitude diagrams, with pixels of different colours occupying distinct regions of the host galaxy and its companion. Fitting stellar population models to these colours, we have estimated the age of each population. We find three distinct groups of ages: an old populationin the outskirts of the host galaxy; an intermediate-age populationaround the nucleus and tidal tail, and a young populationin the nucleus and blue knots.The spectrum of the nucleus shows numerous strong emission lines, including[O i]λ6300,[O ]λ3727,[S ii]λλ6716, 6731, Hα and[N ii]λλ6548, 6583, characteristic of a low-ionization nuclear emission-line region (LINER) spectrum. The companion galaxy shows much narrower emission lines with very different line ratios, characteristic of a starburst galaxy.We have evidence for three distinct episodes of star formation in B1221−423. The correlation of age with position suggests the two most recent episodes were triggered by tidal interactions with the companion galaxy. The evidence points to the active galactic nucleus (AGN) in the centre of B1221−423 having been caught in the act of ignition. However, none of the components we have identified is as young as the radio source, implying that the delay between the interaction and the triggering of the AGN is at least. [ABSTRACT FROM AUTHOR]

We have used the Australia Telescope Compact Array (ATCA) to search for faint radio sources in a ∼3deg² region of sky covered by the 2dF Galaxy Redshift Survey (2dFGRS). Over the region surveyed, the 1σ noise level at 1.4 GHz ranges from 20 μJy to 1 mJy. The survey region includes 365 2dFGRS galaxies, of which 316 have good-quality spectra (176 early-type galaxies or active galactic nuclei, and 140 star-forming galaxies). The fraction of 2dFGRS galaxies detected as radio sources in our survey rises from ∼4 per cent at a 3σ detection limit of 0.3 mJy to 12 per cent at 75 μJy, with roughly equal numbers of star-forming galaxies and active galactic nuclei (AGNs) being detected. The radio luminosity function derived from this sample agrees with earlier determinations, and we find that while the mean redshift of the radio-detected galaxies increases toward lower flux densities for star-forming galaxies, it remains roughly constant for the AGN/early-type radio detections. We discuss possible observing strategies for a submJy radio survey of a larger 2dFGRS region, and show that a survey covering 100 deg² could measure the global evolution of the star formation density to z ∼0.1 in a way which is less affected by reddening than traditional measurements using optical emission lines and ultraviolet photometry. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper is the second in a series describing the Sydney University Molonglo Sky Survey (SUMSS) being carried out at 843 MHz with the Molonglo Observatory Synthesis Telescope (MOST). The survey will consist of ∼590 4.3°× 4.3° mosaic images with 45 × 45 cosec|δ| arcsec[sup 2] resolution, and a source catalogue. In this paper we describe the initial release (version 1.0) of the source catalogue consisting of 107 765 radio sources made by fitting elliptical Gaussians in 271 SUMSS 4.3°× 4.3° mosaics to a limiting peak brightness of 6 mJy beam[sup -1] at δ≤-50° and 10 mJy beam[sup -1] at δ > -50° . The catalogue covers approximately 3500 deg[sup 2] of the southern sky with δ≤-30° , about 43 per cent of the total survey area. Positions in the catalogue are accurate to within 1–2 arcsec for sources with peak brightness A[sub 843]≥ 20 mJy beam[sup -1] and are always better than 10 arcsec. The internal flux density scale is accurate to within 3 per cent. Image artefacts have been classified using a decision tree, which correctly identifies and rejects spurious sources in over 96 per cent of cases. Analysis of the catalogue shows that it is highly uniform and is complete to 8 mJy at δ≤-50° and 18 mJy at δ > -50° . In this release of the catalogue about 7000 sources are found in the overlap region with the National Radio Astronomy Observatories Very Large Array Sky Survey at 1.4 GHz. We calculate a median spectral index of α=-0.83 between 1.4 GHz and 843 MHz. This version of the catalogue will be released via the World Wide Web with future updates as new mosaics are released. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article about epidermolysis bullosa acquisita, which appeared within the issue.