Unmasking damped Ly$\alpha$ absorbing galaxies at $z<1$

Abstract

I review current results from searching for galaxies giving rise to damped Ly$\alpha$ absorbers (DLAs) at $z<1$. Using 14 confirmed DLA galaxies, I further show that intermediate-redshift galaxies possess a large H I envelope out to $24-30\ h^{-1}$ kpc in radius. The photometric and spectral properties of these galaxies confirm that DLA galaxies are drawn from the typical field population, and not from a separate population of low surface brightness or dwarf galaxies. The spatial distribution of metals in the cold ISM of intermediate-redshift galaxies is characterised by a radial gradient of $-0.041\pm 0.012$ dex per kiloparsec (or equivalently a scale length of $10.6\ h^{-1}$ kpc) to $30\ h^{-1}$ kpc radius based on an ensemble of six galaxy-DLA pairs. Adopting this abundance gradient and known $N({\rm H I})$ profiles of nearby galaxies, I show that the observed low metal content of the DLA population can arise naturally as a combination of gas cross-section selection and metallicity gradients commonly observed in local disk galaxies.