Some Like It Hot: Linking Diffuse X-ray Luminosity, Baryonic Mass, and Star Formation Rate in Compact Groups of Galaxies

Compact groups of galaxies (CGs) are ideal laboratories in which to study the effects of environmentally-driven galaxy evolution due to their high galaxy number densities and low velocity dispersions, which cause frequent and prolonged galaxy-galaxy interactions. In our study to better understand the origin and properties of hot gas in poor systems of galaxies, we present an analysis of the diffuse X-ray emission in a sample of 19 CGs observed with the Chandra X-Ray Observatory. Our analysis shows that the hottest, most X-ray luminous CGs agree well with the galaxy cluster X-ray scaling relations, even in CGs where the hot gas is clearly associated with the brightest galaxy. Using Spitzer photometry, we compute stellar masses and combine them with HI masses from the literature to find that high-baryonic-mass CGs are often X-ray luminous, while lower-mass CGs only sometimes exhibit faint X-ray emission attributed to star formation. We also use a new physically motivated definition of fossil groups (evolved galaxy groups where most of the mass is concentrated within a single galaxy) to investigate the hot gas properties of three compact fossil systems in our sample. In addition, we find that the most X-ray luminous CGs have the lowest star formation rates, likely because the cold gas has been exhausted in star formation, heated to X-ray temperatures, or removed from the galaxies by ram-pressure stripping. Finally, the optical colors that trace the recent star formation histories of the most massive group galaxies do not correlate with the X-ray luminosities of the CGs, indicating that perhaps the current state of the X-ray halos is not dependent on the recent assembly of stellar mass in the most massive galaxies. This work has been supported by the Natural Science and Engineering Research Council of Canada, the Ontario Early Researcher Award Program, and NASA.