* Astronomy

Title: Warm-hot gas in groups and galaxies toward H2356-309
Authors: Rik J. Williams, John S. Mulchaey, Juna A. Kollmeier (Carnegie Observatories)

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 harbour 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 virialised 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.

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