The Mass and Absorption Column Densities of Galactic Gaseous Halos. II. The High Ionization State Ions

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, 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 O VI. 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 O VI, {log} {M}_\star =9.5{--}10.5 for Ne VIII, and higher for higher ionization state ions (assuming {T}_\max =2{T}_vir}). A comparison with the observed O VI 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 Ne VIII column density distribution, suggesting that 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 column densities between our models and observations indicate that absorption by the intragroup (cluster) medium and intergalactic medium is also a contributor to the total column density distributions.