Search

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 present a Wide-field ASKAP L-Band Legacy All-sky Blind surveY (WALLABY) study of the nearby (v sys  = 915 km s−1) spiral galaxy IC 5201 using the Australian Square Kilometre Array Pathfinder (ASKAP). IC 5201 is a blue, barred spiral galaxy that follows the known scaling relations between stellar mass, SFR, H  i mass, and diameter. We create a four-beam mosaicked H  i image cube from 175 h of observations made with a 12-antenna sub-array. The root mean square noise level of the cube is 1.7 mJy beam−1 per channel, equivalent to a column density of |$N_{\rm H\, \small {I}}$|  = 1.4 × 1020 cm−2 over 25 km s−1. We report nine extragalactic H  i detections – five new H  i detections including the first velocity measurements for two galaxies. These sources are IC 5201, three dwarf satellite galaxies, two galaxies, and a tidal feature belonging to the NGC 7232/3 triplet and two potential infalling galaxies to the triplet. There is evidence of a previous tidal interaction between IC 5201 and the irregular satellite AM 2220−460. A close fly-by is likely responsible for the asymmetric optical morphology of IC 5201 and warping its disc, resulting in the irregular morphology of AM 2220−460. We quantify the H  i kinematics of IC 5201, presenting its rotation curve as well as showing that the warp starts at 14 kpc along the major axis, increasing as a function of radius with a maximum difference in position angle of 20°. There is no evidence of stripped H  i , triggered or quenched star formation in the system as measured using DECam optical and GALEX UV photometry. [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]

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. [ABSTRACT FROM AUTHOR]

We present Gemini Multi-Object Spectrograph spectra of H  i -rich tidal features located around the outskirts of two interacting galaxy pairs, NGC 3166/9 and NGC 4725/47. These follow-up observations are part of a multiwavelength campaign to study the properties and frequency of tidal dwarf galaxies (TDGs) in group environments. Based on the calculated gas-phase metallicity and redshift, in addition to the previously measured H  i and stellar properties, we have confirmed the tidal origins of TDG candidate AGC 208457, which has emerged from the tidal debris of an interaction between the NGC 3166/9 galaxy pair. By comparing H  i and optical recessional velocities, we have also confirmed a physical association of the gaseous knots and star clusters embedded in the metal-rich tidal tail of NGC 4747. [ABSTRACT FROM AUTHOR]

We present Giant Metrewave Radio Telescope H i observations and deep Canada–France–Hawaii Telescope (CFHT) MegaCam optical images of the gas-rich interacting galaxy group NGC 871/NGC 876/NGC 877 (hereafter NGC 871/6/7). Our high-resolution data sets provide a census of the H i and stellar properties of the detected gas-rich group members. In addition to a handful of spiral, irregular and dwarf galaxies, this group harbours an intriguing H i feature, AGC 749170, that has a gas mass of ∼109.3 M⊙, a dynamical-to-gas mass ratio of ∼1 (assuming that the cloud is rotating and in dynamical equilibrium) and no optical counterpart in previous imaging. Our observations have revealed a faint feature in the CFHT g′ and r′ bands; if it is physically associated with AGC 749170, the latter has $M/L_{\rm g} >1000 \,\mathrm{M}_{{\odot }}/\mathrm{L}_{{\odot }}$ as well as a higher metallicity (estimated using photometric colours) and a significantly younger stellar population than the other low-mass gas-rich group members. These properties, as well as its spectral and spatial location with respect to its suspected parent galaxies, strongly indicate a tidal origin for AGC 749170. Overall, the H i properties of AGC 749170 resemble those of other optically dark/dim clouds that have been found in groups. These clouds could represent a class of relatively long-lived H i-rich tidal remnants that survive in intermediate-density environments. [ABSTRACT FROM PUBLISHER]