High-redshift damped Ly α absorbing galaxy model reproducing the N H I − Z distribution

Abstract

ABSTRACT We investigate how damped Lyman α absorbers (DLAs) at $z$ ∼ 2 − 3, detected in large optical spectroscopic surveys of quasars, trace the population of star-forming galaxies. Building on previous results, we construct a model based on observed and physically motivated scaling relations in order to reproduce the bivariate distributions of metallicity, Z, and H i column density, $N_{\rm H\, \rm{\small {I}}}$. Furthermore, the observed impact parameters for galaxies associated to DLAs are in agreement with the model predictions. The model strongly favours a metallicity gradient, which scales with the luminosity of the host galaxy, with a value of γ* = −0.019 ± 0.008 dex kpc−1 for L* galaxies that gets steeper for fainter galaxies. We find that DLAs trace galaxies over a wide range of galaxy luminosities, however, the bulk of the DLA cross-section arises in galaxies with L ∼ 0.1 L* at $z$ ∼ 2.5 consistent with numerical simulations.