Connection between Galaxies and Neutral Gas Outside Galaxies

Gaseous halos of galaxies and their interaction with their environments such as the intra-group or intergalactic medium are fundamental to our understanding of how galaxies get their gas. It has long been recognized that observed star-formation histories and stellar population metallicities require significant on-going accretion of cool gas into galaxies in the present epoch (e.g., the G-dwarf problem). Recently, theoretical studies by Maller & Bullock 2004, Keres et al. 2005, and others have reignited the debate about how galaxies acquire their gas and thereby fuel star formation. In addition, this also alleviates the missing-baryons problem because many of the baryons are left behind in a difficult-to-observes state in the halos as well as the intra-group medium and/or inter-galactic medium.

In my talk I'll discuss our observations of neutral gas in these environments. First, I'll talk about our detection of diffuse neutral hydrogen in harsh environment of the Hickson Compact Groups as well as in a loose group. Our theoretical calculations suggest that tidal debris can survive for more than ~0.5 Gys in these environments. Secondly, I'll also talk our ongoing efforts on detection 21cm HI absorbers from the halos and disks of galaxies. In particular, I'll discuss our GBT-VLA-VLBA pilot project where we detected and mapped an HI absorber associated with a dwarf(ish) spiral galaxy at a projected distance of 1.7 kpc from galaxy center.