case western reserve university



Unmasking Damped Lya Absorbing Galaxies

Hsiao-Wen Chen (MIT)

I will present current results from searching for galaxies giving rise to damped DLA absorbers (DLAs) at z<1. Using 14 galaxies that are known to produce DLA features in the spectra of background QSOs, I will show that intermediate-redshift galaxies possess large HI envelope out to 24-30 h^{-1} kpc radius. In addition, 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. Comparisons of the ISM abundances of the DLA galaxies and the metallicities of the absorbers at large galactic radii suggest that some DLAs originate in the relatively unevolved outskirts of galactic disks. An abundance profile characterized by a radial gradient of -0.041+/-0.012 dex per kiloparsec (or equivalently a scale length of 10.6 h^{-1} kpc) is found from galactic center to 30 h^{-1} kpc radius based on an ensemble of six galaxy-DLA pairs. Finally adopting this abundance gradient and known N(HI) profiles of nearby galaxies, I will show that the on-average 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.