The Mass and Absorption Columns of Galactic Gaseous Halos II -- The High Ionization State Ions

TL;DR

This paper models the distribution of high ionization-state ions in galactic gaseous halos, showing how their column densities relate to galaxy mass, temperature, and cosmic evolution, and compares predictions with observations.

Contribution

It introduces a refined model linking high ionization ions to galaxy properties and compares different halo radius assumptions with observed data.

Findings

The model reproduces the observed column density distribution shape.

High column density systems are linked to galaxies with specific virial temperatures.

The large radius model fits { ext{OVI}} data better, but conflicts with { ext{NeVIII}} observations.

Abstract

The high ionization-state ions trace the hot gases in the universe, of which gaseous halos around galaxies are a major contributor. Following Qu & Bregman (2018), we calculate the gaseous halo contribution to the observed column density distributions for these ions by convolving the gaseous halo model with the observed stellar mass function. The predicted column density distribution reproduces the general shape of the observed column density distribution -- a broken power law with the break point at $\log N=14.0$ for {\OVI}. Our modeling suggests that the high column density systems originate from galaxies for which the virial temperature matches the temperature of the ionization fraction peak. Specifically, this mass range is $\log M_\star=8.5-10$ for {\OVI}, $\log M_\star=9.5-10.5$ for {\NeVIII}, and higher for higher ionization state ions (assuming $T_{\rm max}=2T_{\rm vir}$). A comparison with the observed {\OVI} column density distribution prefers a large radius model, where the maximum radius is twice the virial radius. This model may be in conflict with the more poorly defined {\NeVIII} column density distribution, suggesting further observations are warranted. The redshift evolution of the high column density systems is dominated by the change of the cosmic star formation rate, which decreases from $z=1.0$ to the local universe. Some differences at lower columns between our models and observations indicate that absorption by the intra-group (cluster) medium and intergalactic medium are also contributors to the total column density distributions.