On the nature of the z=0 X-ray absorbers: II. The contrast between local and AGN host galaxy absorption

Abstract

We search for highly-ionized gas near three AGN host galaxies using the Chandra low-energy transmission grating spectrograph. Strong absorption lines from such gas are seen at z=0, most likely from one or more of the following components: (1) a Galactic corona, (2) the Local Group medium, and (3) an extended warm-hot intergalactic medium (WHIM) filament passing through our local overdensity. Since AGNs reside within host galaxies that are also expected to sit within cosmically overdense regions, similar absorption resulting from these three components should appear at the AGN redshifts as well. However, no such absorption is seen. The lack of strong absorption lines is likely a result of the gas in these host galaxies and surrounding galaxy clusters being much hotter, and hence more highly ionized, than the gas in the Local Group+Galaxy system. We conclude that WHIM filaments produce no measurable absorption lines at the AGN redshifts, and therefore contribute at most a small fraction of the observed z=0 warm-hot gas.