HI-deficient galaxies in intermediate density environments

Observations show that spiral galaxies in galaxy clusters tend to have on average less neutral hydrogen (HI) than galaxies of the same type and size in the field. There is accumulating evidence that such HI-deficient galaxies are also relatively frequent in galaxy groups. An important question is, which mechanisms are responsible for the gas deficiency in galaxy groups. To gain a better understanding of how environment affects the gas content of galaxies, we identified a sample of six HI-deficient galaxies from the HI Parkes All Sky Survey (HIPASS) using HI-optical scaling relations. One of the galaxies is located in the outskirts of the Fornax cluster, four are in loose galaxy groups and one is in a galaxy triplet. We present new high resolution HI observations with the Australia Telescope Compact Array (ATCA) of these galaxies. We discuss the possible cause of HI-deficiency in these galaxies based on HI observations and various multi-wavelength data. We find that the galaxies have truncated HI disks, lopsided gas distribution and some show asymmetries in their stellar disks. We conclude that both ram pressure stripping and tidal interactions are important gas removal mechanisms in low density environments.Comment: Accepted to MNRAS, 17 pages, 10 figures, 7 table

Blasting away a dwarf galaxy: the \u27tail\u27 of ESO 324-G024

We present Australia Telescope Compact Array radio data of the dwarf irregular galaxy ESO 324-G024 which is seen in projection against the giant, northern lobe of the radio galaxy Centaurus A (Cen A, NGC 5128). The distorted morphology and kinematics of ESO 324-G024, as observed in the 21 cm spectral line emission of neutral hydrogen, indicate disruptions by external forces. We investigate whether tidal interactions and/or ram pressure stripping are responsible for the formation of the H Itail stretching to the north-east of ESO 324-G024 with the latter being most probable. Furthermore, we closely analyse the sub-structure of Cen A\u27s polarized radio lobes to ascertain whether ESO 324-G024 is located in front, within or behind the northern lobe. Our multiwavelength, multicomponent approach allows us to determine that ESO 324-G024 is most likely behind the northern radio lobe of Cen A. This result helps to constrain the orientation of the lobe, which is likely inclined to our line of sight by approximately 60° if NGC 5128 and ESO 324-G024 are at the same distance

H I-deficient galaxies in intermediate-density environments

Observations show that spiral galaxies in galaxy clusters tend to have on average less neutral hydrogen (H I) than galaxies of the same type and size in the field. There is accumulating evidence that such H I-deficient galaxies are also relatively frequent in galaxy groups. An important question is that which mechanisms are responsible for the gas deficiency in galaxy groups. To gain a better understanding of how environment affects the gas content of galaxies, we identified a sample of six H I-deficient galaxies from the H I Parkes All Sky Survey (HIPASS) using H I-optical scaling relations. One of the galaxies is located in the outskirts of the Fornax cluster, four are in loose galaxy groups and one is in a galaxy triplet. We present new high-resolution H I observations with the Australia Telescope Compact Array (ATCA) of these galaxies. We discuss the possible cause of H I-deficiency in the sample based on H I observations and various multi-wavelength data. We find that the galaxies have truncated H I discs, lopsided gas distribution and some show asymmetries in their stellar discs. We conclude that both ram-pressure stripping and tidal interactions are important gas removal mechanisms in low-density environments

Gaseous Tidal Debris found in the NGC 3783 Group

We have conducted wide-field HI mapping of a ~5.5 x 5.5 degree region surrounding the NGC 3783 galaxy group, to an HI mass limit of ~4 x 10^8 Msun. The observations were made using the multibeam system on the Parkes 64-m radiotelescope, as part of the Galaxy Evolution Multiwavelength Study (GEMS). We find twelve HI detections in our Parkes data, four more than catalogued in HIPASS. We find two new group members, and discover an isolated region of HI gas with an HI mass of ~4 x 10^8 Msun, without a visible corresponding optical counterpart. We discuss the likelihood of this HI region being a low surface brightness galaxy, primordial gas, or a remnant of tidal debris. For the NGC 3783 group we derive a mean recession velocity of 2903 km/s, and a velocity dispersion of 190 km/s. The galaxy NGC 3783 is the nearest galaxy to the luminosity weighted centre of the group, and is at the group mean velocity. From the X-ray and dynamical state of this galaxy group, this group appears to be in the early stages of its evolution.Comment: 12 pages, MNRAS accepted: full resolution paper available at http://astronomy.swin.edu.au/~vkilborn/MF1350rv.pd

Gemini Follow-up of two massive HI clouds discovered with the Australian Square Kilometer Array Pathfinder

Using the Gemini Multi Object Spectrograph (GMOS) we search for optical counterparts of two massive (~10^9 solar masses) neutral hydrogen clouds near the spiral galaxy IC 5270, located in the outskirts of the IC 1459 group. These two HI clouds were recently discovered using the Australian Square Kilometer Array Pathfinder (ASKAP). Two low surface brightness optical counterparts to one of these HI clouds are identified in the new Gemini data that reaches down to magnitudes of ~27.5 mag in the g-band. The observed HI mass to light ratio derived with these new data, M_(HI)/L_g =242, is among the highest reported to date. We are also able to rule out that the two HI clouds are dwarf companions of IC 5270. Tidal interactions and ram pressure stripping are plausible explanations for the physical origin of these two clouds.Comment: The journal version contains high-resolution images: http://iopscience.iop.org/article/10.3847/2041-8213/aaaa1

WALLABY early science − V. ASKAP HI imaging of the Lyon Group of Galaxies 351

We present an HI 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 HI sources that are not presented in previous optical catalogues. 23 out of 40 sources have new redshifts derived from the new HI 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 HI emission is seen in six galaxies indicating interaction within the group, although no HI debris is found. We also detect HI 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