HI-selected Galaxies as a probe of Quasar Absorption Systems

TL;DR

This study uses semi-analytic models to link HI-rich galaxies with quasar absorption systems, revealing how galaxy properties relate to DLA and sub-DLA systems and their implications for galaxy evolution.

Contribution

It demonstrates the connection between HI-selected galaxies and quasar absorption systems, especially DLA and sub-DLA, using detailed modeling and comparison.

Findings

HI-selected galaxies with M(HI) > 10^8 solar masses have DLA-like HI column densities.

Star formation rates correlate more strongly with HI mass than luminosity.

Sub-DLA galaxies dominate at lower HI masses, providing insights into galaxy evolution.

Abstract

We investigate the properties of HI-rich galaxies detected in blind radio surveys within the hierarchical structure formation scenario using a semi-analytic model of galaxy formation. By drawing a detailed comparison between the properties of HI-selected galaxies and HI absorption systems, we argue a link between the local galaxy population and quasar absorption systems, particularly for Damped Ly-alpha absorption (DLA) systems and sub-DLA systems. First, we evaluate how many HI-selected galaxies exhibit HI column densities as high as those of DLA systems. We find that HI-selected galaxies with HI masses M(HI) > 10^8 solar masses have gaseous disks that produce HI column densities comparable to those of DLA systems. We conclude that DLA galaxies where the HI column densities are as high as those of DLA systems, contribute significantly to the population of HI-selected galaxies at M(HI) > 10^8 solar masses. Second, we find that star formation rates (SFRs) correlate tightly with HI masses rather than B- (and J-) band luminosities. In the low-mass range M(HI) < 10^8 solar masses, sub-DLA galaxies replace DLA galaxies as the dominant population. The number fraction of sub-DLA galaxies relative to galaxies reaches 40%-60% at HI masses 10^8 solar masses and 30%-80% at 10^7 solar masses. The HI-selected galaxies at 10^7 solar masses are a strong probe of sub-DLA systems that place stringent constraints on galaxy formation and evolution.