The Warm Circum-Galactic Medium: 10^5-6 K Gas Associated with a Single
  Galaxy Halo or with an Entire Group of Galaxies?
  In preparation for a Hubble Space Telescope (HST) observing project using the
Cosmic Origins Spectrograph (COS), the positions of all AGN targets having
high-S/N far-UV G130M spectra were cross-correlated with a large catalog of
low-redshift galaxy groups homogeneously selected from the spectroscopic sample
of the Sloan Digital Sky Survey (SDSS). Searching for targets behind only those
groups at z = 0.1-0.2 (which places the OVI doublet in the wavelength region of
peak COS sensitivity) we identified only one potential S/N = 15-20 target, FBQS
1010+3003. An OVI-only absorber was found in its G130M spectrum at z = 0.11326,
close to the redshift of a foreground small group of luminous galaxies at z =
0.11685. Because there is no associated Lyalpha absorption, any
characterization of this absorber is necessarily minimal; however, the OVI
detection likely traces "warm" gas in collisional ionization equilibrium at T ~
300,000 K. While this discovery is consistent with being interface gas between
cooler, photoionized clouds and a hotter intra-group medium, it could also be
warm, interface gas associated with the circum-galactic medium (CGM) of the
single closest galaxy. In this case a detailed analysis of the galaxy
distribution (complete to 0.2 L*) strongly favors the individual galaxy
association. This analysis highlights the necessity of both high-S/N > 20 COS
data and a deep galaxy redshift survey of the region in order to test more
rigorously the association of OVI-absorbing gas with a galaxy group. A Cycle 23
HST/COS program currently is targeting 10 UV-bright AGN behind 12 low-redshift
galaxy groups to test the warm, group gas hypothesis.
