The HI in Ring Galaxies Survey (HI-RINGS) -- Effects of the bar on the HI gas in ring galaxies

We present a new high-resolution neutral atomic hydrogen (HI) survey of ring galaxies using the Australia Telescope Compact Array (ATCA). We target a sample of 24 ring galaxies from the Buta (1995) Southern Ring Galaxy Survey Catalogue in order to study the origin of resonance-, collisional- and interaction-driven ring galaxies. In this work, we present an overview of the sample and study their global and resolved HI properties. In addition, we also probe their star formation properties by measuring their star formation rates (SFR) and their resolved SFR surface density profiles. We find that a majority of the barred galaxies in our sample are HI deficient, alluding to the effects of the bar in driving their HI deficiency. Furthermore, for the secularly evolving barred ring galaxies in our sample, we apply Lindblad's resonance theory to predict the location of the resonance rings and find very good agreement between predictions and observations. We identify rings of HI gas and/or star formation co-located at one or the other major resonances. Lastly, we measure the bar pattern speed ($\Omega_{\textrm{bar}}$) for a sub-sample of our galaxies and find that the values range from 10 -- 90 km s$^{-1}$ kpc$^{-1}$, in good agreement with previous studies.Comment: Accepted for publication in PAS

The neutral hydrogen properties of galaxies in gas-rich groups

We present an analysis of the integrated neutral hydrogen (H I) properties for 27 galaxies within nine low-mass, gas-rich, late-type dominated groups which we denote 'Choirs'. We find that majority of the central Choir galaxies have average H I content: they have a normal gas-mass fraction with respect to isolated galaxies of the same stellar mass. In contrast, we find more satellite galaxies with a lower gas-mass fraction than isolated galaxies of the same stellar mass. A likely reason for the lower gas content in these galaxies is tidal stripping. Both the specific star formation rate and the star formation efficiency of the central group galaxies are similar to galaxies in isolation. The Choir satellite galaxies have similar specific star formation rate as galaxies in isolation, therefore satellites that exhibit a higher star formation efficiency simply owe it to their lower gas-mass fractions. We find that the most H I massive galaxies have the largest H I discs and fall neatly on to the H I size-mass relation, while outliers are galaxies that are experiencing interactions. We find that high specific angular momentum could be a reason for galaxies to retain the large fraction of H I gas in their discs. This shows that for the Choir groups with no evidence of interactions, as well as those with traces of minor mergers, the internal galaxy properties dominate over the effects of residing in a group. The probed galaxy properties strengthen evidence that the Choir groups represent the early stages of group assembly

The Neutral Hydrogen Properties of Galaxies in Gas-rich Groups

The majority of galaxies in the local Universe lie within a group environment - thus it is important to understand the group environmental impact on galaxy evolution. Our multi-wavelength survey of Choir groups probes low mass, gas-rich, late-type dominated groups with one or two giant spirals and a number of dwarf galaxies. These groups are reminiscent of (though more gas-rich) our local group. In this talk I will reveal the neutral hydrgogen (HI) content in the Choir groups. I will show that the majority of galaxies in these groups are gas-rich and that those in non-interacting groups are dominated by their internal galaxy properties rather than the group environment. Only a couple of galaxies are gas-poor which is most likely due to tidal interactions. To place Choir groups in the larger scale context, I will present detailed analysis of two extreme groups: an isolated Choir group, and a cluster infalling Choir group