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We present a pilot study of the atomic neutral hydrogen gas (H  i) content of ultra-diffuse galaxy (UDG) candidates. In this paper, we use the pre-pilot Eridanus field data from the Widefield ASKAP L -band Legacy All-sky Blind Survey to search for H  i in UDG candidates found in the Systematically Measuring Ultra-diffuse Galaxies survey (SMUDGes). We narrow down to 78 SMUDGes UDG candidates within the maximum radial extents of the Eridanus subgroups for this study. Most SMUDGes UDGs candidates in this study have effective radii smaller than 1.5 kpc and thus fail to meet the defining size threshold. We only find one H  i detection, which we classify as a low-surface-brightness dwarf. Six putative UDGs are H  i -free. We show the overall distribution of SMUDGes UDG candidates on the size–luminosity relation and compare them with low-mass dwarfs on the atomic gas fraction versus stellar mass scaling relation. There is no correlation between gas-richness and colour indicating that colour is not the sole parameter determining their H  i content. The evolutionary paths that drive galaxy morphological changes and UDG formation channels are likely the additional factors to affect the H  i content of putative UDGs. The actual numbers of UDGs for the Eridanus and NGC 1332 subgroups are consistent with the predicted abundance of UDGs and the halo virial mass relation, except for the NGC 1407 subgroup, which has a smaller number of UDGs than the predicted number. Different group environments suggest that these putative UDGs are likely formed via the satellite accretion scenario. [ABSTRACT FROM AUTHOR]

We study the tidal interaction of galaxies in the Eridanus supergroup, using H i data from the pre-pilot survey of the Widefield ASKAP L -band Legacy All-sky Blind surveY. We obtain optical photometric measurements and quantify the strength of tidal perturbation using a tidal parameter S sum. For low-mass galaxies of M * ≲ 109 M ⊙, we find a dependence of decreasing H i to optical disk size ratio with increasing S sum, but no dependence of H i spectral line asymmetry with S sum. This is consistent with the behavior expected under tidal stripping. We confirm that the color profile shape and color gradient depend on the stellar mass, but there is an additional correlation of low-mass galaxies having their color gradients within 2 R 50 increasing with higher S sum. For these low-mass galaxies, the dependence of color gradients on S sum is driven by the color becoming progressively redder in the inner disk when tidal perturbations are stronger. For high-mass galaxies, there is no dependence of color gradients on S sum, and we find a marginal reddening throughout the disks with increasing S sum. Our result highlights tidal interaction as an important environmental effect in producing the faint end of the star formation suppressed sequence in galaxy groups. [ABSTRACT FROM AUTHOR]

We present results from our analysis of the Hydra I cluster observed in neutral atomic hydrogen (H  i) as part of the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY). These WALLABY observations cover a 60-square-degree field of view with uniform sensitivity and a spatial resolution of 30 arcsec. We use these wide-field observations to investigate the effect of galaxy environment on H  i gas removal and star formation quenching by comparing the properties of cluster, infall, and field galaxies extending up to ∼5 R 200 from the cluster centre. We find a sharp decrease in the H  i -detected fraction of infalling galaxies at a projected distance of ∼1.5 R 200 from the cluster centre from |$\sim 85{{\ \rm per\ cent}}$| to |$\sim 35{{\ \rm per\ cent}}$|⁠. We see evidence for the environment removing gas from the outskirts of H  i -detected cluster and infall galaxies through the decrease in the H  i to r -band optical disc diameter ratio. These galaxies lie on the star-forming main sequence, indicating that gas removal is not yet affecting the inner star-forming discs and is limited to the galaxy outskirts. Although we do not detect galaxies undergoing galaxy-wide quenching, we do observe a reduction in recent star formation in the outer disc of cluster galaxies, which is likely due to the smaller gas reservoirs present beyond the optical radius in these galaxies. Stacking of H  i non-detections with H  i masses below |$M_{\rm {HI}}\lesssim 10^{8.4}\, \rm {M}_{\odot }$| will be required to probe the H  i of galaxies undergoing quenching at distances ≳60 Mpc with WALLABY. [ABSTRACT FROM AUTHOR]

We present the Australian Square Kilometre Array Pathfinder (ASKAP) WALLABY pre-pilot observations of two 'dark' H  i sources (with H  i masses of a few times 108  |$\rm {M}_\odot$| and no known stellar counterpart) that reside within 363 kpc of NGC 1395, the most massive early-type galaxy in the Eridanus group of galaxies. We investigate whether these 'dark' H  i sources have resulted from past tidal interactions or whether they are an extreme class of low surface brightness galaxies. Our results suggest that both scenarios are possible, and not mutually exclusive. The two 'dark' H  i sources are compact, reside in relative isolation, and are more than 159 kpc away from their nearest H  i -rich galaxy neighbour. Regardless of origin, the H  i sizes and masses of both 'dark' H  i sources are consistent with the H  i size–mass relationship that is found in nearby low-mass galaxies, supporting the possibility that these H  i sources are an extreme class of low surface brightness galaxies. We identified three analogues of candidate primordial 'dark' H  i galaxies within the TNG100 cosmological, hydrodynamic simulation. All three model analogues are dark matter dominated, have assembled most of their mass 12–13 Gyr ago, and have not experienced much evolution until cluster infall 1–2 Gyr ago. Our WALLABY pre-pilot science results suggest that the upcoming large-area H  i surveys will have a significant impact on our understanding of low surface brightness galaxies and the physical processes that shape them. [ABSTRACT FROM AUTHOR]

We present observations of the Eridanus supergroup obtained with the Australian Square Kilometre Array Pathfinder (ASKAP) as part of the pre-pilot survey for the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY). The total number of detected H  i sources is 55, of which 12 are background galaxies not associated with the Eridanus supergroup. Two massive H  i clouds are identified and large H  i debris fields are seen in the NGC 1359 interacting galaxy pair, and the face-on spiral galaxy NGC 1385. We describe the data products from the source finding algorithm and present the basic parameters. The presence of distorted H  i morphology in all detected galaxies suggests ongoing tidal interactions within the subgroups. The Eridanus group has a large fraction of H  i -deficient galaxies as compared to previously studied galaxy groups. These H  i -deficient galaxies are not found at the centre of the group. We find that galaxies in the Eridanus supergroup do not follow the general trend of the atomic gas fraction versus stellar mass scaling relation, which indicates that the scaling relation changes with environmental density. In general, the majority of these galaxies are actively forming stars. [ABSTRACT FROM AUTHOR]

We report the discovery of large amounts of previously undetected cold neutral atomic hydrogen (H  i) around the core triplet galaxies in the nearby NGC 7232 galaxy group with MeerKAT. With a physical resolution of ∼1 kpc, we detect a complex web of low-surface-brightness H  i emission down to a 4 σ column density level of ∼1 × 1019 cm−2 (over 44  km s−1). The newly discovered H  i streams extend over ∼20 arcmin corresponding to 140 kpc in projection. This is approximately three times the H  i extent of the galaxy triplet (52 kpc). The H  i debris has an H  i mass of ∼6.6 × 109 M⊙, more than 50 per cent of the total H  i mass of the triplet. Within the galaxy triplet, NGC 7233 and NGC 7232 have lost a significant amount of H  i while NGC 7232B appears to have an excess of H  i. The H  i deficiency in NGC 7232 and NGC 7233 indicates that galaxy–galaxy interaction in the group concentrates on this galaxy pair while the other disc galaxies have visited them over time. In comparison to the AMIGA sample of isolated galaxies, we find that with regards to its total H  i mass the NGC 7232/3 galaxy triplet is not H  i -deficient. Despite the many interactions associated to the triplet galaxies, no H  i seems to have been lost from the group (yet). [ABSTRACT FROM AUTHOR]

We present results from neutral atomic hydrogen (H  i) observations of Hydra I, the first cluster observed by the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) on the Australian Square Kilometre Array Pathfinder. For the first time, we show that WALLABY can reach its final survey sensitivity. Leveraging the sensitivity, spatial resolution, and wide field of view of WALLABY, we identify a galaxy, ESO 501−G075, that lies near the virial radius of Hydra I and displays an H  i tail. ESO 501−G075 shows a similar level of morphological asymmetry as another cluster member, which lies near the cluster centre and shows signs of experiencing ram pressure. We investigate possible environmental processes that could be responsible for producing the observed disturbance in the H  i morphology of ESO 501−G075. We rule out tidal interactions, as ESO 501−G075 has no nearby neighbours within ∼0.34 Mpc. We use a simple model to determine that ram pressure can remove gas from the disc at radii r ≳ 25 kpc. We conclude that, as ESO 501−G075 has a typical H  i mass compared to similar galaxies in the field and its morphology is compatible with a ram pressure scenario, ESO 501−G075 is likely recently infalling into the cluster and in the early stages of experiencing ram pressure. [ABSTRACT FROM AUTHOR]

This study uses H i image data from the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY) pilot survey with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, covering the Hydra cluster out to 2.5r200. We present the projected phase–space distribution of H i -detected galaxies in Hydra, and identify that nearly two-thirds of the galaxies within may be in the early stages of ram pressure stripping. More than half of these may be only weakly stripped, with the ratio of strippable H i (i.e., where the galactic restoring force is lower than the ram pressure in the disk) mass fraction (over total H i mass) distributed uniformly below 90%. Consequently, the H i mass is expected to decrease by only a few 0.1 dex after the currently strippable portion of H i in these systems has been stripped. A more detailed look at the subset of galaxies that are spatially resolved by WALLABY observations shows that, while it typically takes less than 200 Myr for ram pressure stripping to remove the currently strippable portion of H i , it may take more than 600 Myr to significantly change the total H i mass. Our results provide new clues to understanding the different rates of H i depletion and star formation quenching in cluster galaxies. [ABSTRACT FROM AUTHOR]

We present an H  i study of the galaxy group LGG 351 using Widefield ASKAP L -band Legacy All-sky Blind Survey (WALLABY) early science data observed with the Australian Square Kilometre Array Pathfinder (ASKAP). LGG 351 resides behind the M 83 group at a velocity range (cz) of ∼3500–4800 km s−1 within the rich Hydra-Centaurus overdensity region. We detect 40 sources with the discovery of a tidally interacting galaxy pair and two new H  i sources that are not presented in previous optical catalogues. 23 out of 40 sources have new redshifts derived from the new H  i data. This study is the largest WALLABY sub-sample to date and also allows us to further validate the performance of ASKAP and the data reduction pipeline askapsoft. Extended H  i emission is seen in six galaxies indicating interaction within the group, although no H  i debris is found. We also detect H  i in a known ultra-faint dwarf galaxy (dw 1328−29), which demonstrates that it is not a satellite of the M 83 group as previously thought. In conjunction with multiwavelength data, we find that our galaxies follow the atomic gas fraction and baryonic Tully–Fisher scaling relations derived from the GALEX Arecibo SDSS Survey. In addition, majority of our galaxies fall within the star formation main sequence indicating inefficiency of gas removal processes in this loose galaxy group. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

ABSTRACT We present Arecibo Legacy Fast ALFA (ALFALFA) and follow-up Giant Metrewave Radio Telescope (GMRT) H i observations of the gas-rich interacting group NGC 3166/9. The sensitive ALFALFA data provide a complete census of H i-bearing systems in the group while the high-resolution GMRT data elucidate their origin, enabling one of the first unbiased physical studies of gas-rich dwarf companions and the subsequent identification of second-generation, tidal dwarf galaxies in a nearby group. The ALFALFA maps reveal an extended H i envelope around the NGC 3166/9 group core, which we mosaic at higher resolution using six GMRT pointings spanning ∼1 deg2. A thorough search of the GMRT data cube reveals eight low-mass objects with gas masses ranging from 4 × 107 to 3 × 108 M⊙ and total dynamical masses up to 1.4 × 109 M⊙. A comparison of the H i fluxes measured from the GMRT data to those measured in the ALFALFA data suggests that a significant fraction (∼60 per cent) of the H i is smoothly distributed on scales greater than 1 arcmin (∼7 kpc at the NGC 3166/9 distance). We compute stellar masses and star formation rates for the eight low-mass GMRT detections, using ancillary Sloan Digital Sky Survey (SDSS) and Galaxy Evolution Explorer (GALEX) data, and use these values to constrain their origin. Most of the detections are likely to be either pre-existing dwarf irregular galaxies or short-lived, tidally formed knots; however, one candidate, AGC 208457, is clearly associated with a tidal tail extending below NGC 3166, exhibits a dynamical to gas mass ratio close to unity and has a stellar content and star formation rate that are broadly consistent with both simulated as well as candidate tidal dwarf galaxies from the literature. Our observations therefore strongly suggest that AGC 208457 is a tidal dwarf galaxy. [ABSTRACT FROM AUTHOR]