Warm-hot gas in groups and galaxies toward H2356-309. (arXiv:1209.4080v1 [astro-ph.CO])

Warm-hot gas in groups and galaxies toward H2356-309. (arXiv:1209.4080v1 [astro-ph.CO]):
We present a detailed analysis of the galaxy and group distributions around
three reported X-ray absorption line systems in the spectrum of the quasar
H2356-309. Previous studies associated these absorbers with known large-scale
galaxy structures (i.e., walls and filaments) along the line of sight. Such
absorption lines typically trace 10^{5-7} K gas, and may be evidence of the
elusive warm-hot intergalactic medium (WHIM) thought to harbor the bulk of the
low-redshift "missing baryons;" alternatively, they may be linked to individual
galaxies or groups in the filaments. Here we combine existing galaxy survey
data with new, highly complete multi-object Magellan spectroscopy to
investigate the detailed galaxy distribution near each absorber. All of these
three absorption systems nominally lie within the virial radii of nearby
galaxies and/or groups, and could therefore arise in these virialized
structures rather than (or in addition to) the WHIM. However, we find no
additional galaxies near a fourth "void" absorber recently reported by
Zappacosta et al., suggesting that this system may indeed trace gas
unassociated with any individual halo. We therefore conclude that most X-ray
absorbers are coincident with galaxy and/or group environments, though some
could still trace the large-scale filamentary WHIM gas predicted by
simulations.