2004AJ....127..199P

We have conducted a study with the Very Large Array (VLA), the Dominion Radio Astrophysical Observatory Synthesis Telescope, and the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite to search for the intragroup medium in two loose groups of galaxies: GH 144 and GH 158. The VLA observations provide a census of the dense H I content of these groups in the form of individual galaxies and free-floating H I clouds as traced by the 21 cm H I line, while the FUSE observations trace the diffuse neutral and hot ionized gas that may fill the intragroup medium, populate the halos of individual galaxies, or reside in a skin around denser, neutral clouds. While nothing was detected in GH 158, in GH 144 we detected two previously unknown H I-rich low surface brightness group galaxies. In addition, Lyα, Lyβ, C III, and N V were detected toward GH 144. Using this suite of data, we were able to place limits on the mass of various portions of this group. If virialized, GH 144 has a mass of 2x10¹² M_☉. Of that mass, 8% lies in the individual cataloged galaxies, and no more than that same fraction again could lie in the dense, neutral medium as constrained by our VLA observations. The absorption lines imply a diffuse gas with a volume density greater than 10^–5.2/cm3 from a layer less than 22 kpc thick, assuming a metallicity of 0.4 Z_☉. While the extent of this gas is uncertain, it seems unlikely that this diffuse gas contributes a significant fraction of the group mass. Given the depth of the absorbing material and its separation from the nearest galaxies, it seems most likely that it originates from a small clump in the intragroup medium; perhaps an ionized high-velocity cloud, but it may be associated with one of our new H I detections. This was our ambitious first attempt to search for the intergalactic medium in emission and absorption, and while it was only partially successful, we show what is possible and what more is needed for its success.