The Neutral Hydrogen Content of Satellite Galaxies in the Local Volume

Abstract

The properties of the satellite populations of galaxies are vital for understanding their structure and evolution in a cosmological context. Deep optical imaging surveys have revealed a host of low surface brightness (LSB) features near Local Volume galaxies, that may be satellites of the latter. We conduct atomic gas (HI) observations of 48 such satellite candidate galaxies discovered around 10 different hosts using the Robert C. Byrd Green Bank Telescope. Detections of HI reservoirs in these systems will provide spectroscopic distances that can be used to confirm an association to their putative hosts. Non-detections imply that the objects are gas-poor, irrespective of their distance along the line-of-sight. We first search for HI in six ultra-faint dwarf candidates discovered near NGC 3109. One is detected in HI, placing it in the background as a gas-rich field dwarf, while the remaining five have no detectable HI emission. We also searched for HI along the lines of sight to 27 LSB features that project around M101, and the majority (23/27) were found to be gas-poor. The other four were detected in HI, though only one has a recessional velocity consistent with that of M101. Two of the other galaxies have systemic velocities suggesting an association with a background group and the fourth detection places it in the background. Finally, we searched for HI in 15 satellite candidates around 8 hosts finding just one gas-rich satellite. Using the HI and optical properties of all non-detections, we compare them with other samples of dwarf galaxies. We find that in order for our non-detections to be consistent with well-studied scaling relations for gas-rich field galaxies, the most plausible scenario is that the Local Volume LSBs are associated with their hosts, the M101 candidates are associated with it or the background group, and the satellite candidates around NGC 3109 are in fact field galaxies that have distances in the range 17.5-38 Mpc. Therefore, both detections and non-detections place important constraints on the physical properties of candidate satellite galaxies detected in the optical.