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

TL;DR

This study investigates the presence of highly-ionized gas near AGN host galaxies using Chandra spectroscopy, finding that hotter, more ionized gas in these galaxies results in no detectable absorption lines at their redshifts, contrasting with local z=0 absorbers.

Contribution

The paper demonstrates that the absence of absorption lines at AGN redshifts indicates hotter, more ionized gas in host galaxies, contrasting with local z=0 absorbers and refining understanding of the warm-hot intergalactic medium.

Findings

No strong absorption lines detected at AGN redshifts.

Hotter, more ionized gas in host galaxies explains the lack of absorption.

WHIM filaments contribute minimally to z=0 warm-hot gas.

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.