A joint model for the emission and absorption properties of damped Lyman alpha absorption systems

TL;DR

This paper presents a joint model explaining the emission and absorption features of damped Lyman alpha systems at z~3, linking faint Ly alpha emitters to DLA host galaxies and their properties within the $\\Lambda$CDM framework.

Contribution

It introduces a model that successfully reproduces the size distribution and incidence rate of faint Ly alpha emitters as DLA hosts, supporting their identification and elucidating galaxy properties at high redshift.

Findings

Faint Ly alpha emitters likely are DLA host galaxies with specific duty cycles.

Ly alpha cooling contributes little to the emission, which is mainly from star formation.

Galaxies in dark matter halos with velocities 100-150 km/s dominate DLA incidence.

Abstract

The recently discovered population of ultra-faint extended line emitters can account for the majority of the incidence rate of Damped Lyman Alpha systems (DLAs) at z ~ 3 if the line emission is interpreted as Ly alpha. We show here that a model similar to that proposed by Haehnelt, Steinmetz, & Rauch (2000), which explains the incidence rate and kinematics of DLAs in the context of $\Lambda$CDM models for structure formation, also reproduces the size distribution of the new population of faint Ly alpha emitters for plausible parameters. This lends further support to identification of the emitters with the hitherto elusive population of DLA host galaxies. The observed incidence rate of DLAs together with the observed space density and size distribution of the emitters suggest a duty cycle of ~ 0.2 - 0.4 for the Ly alpha emission from DLA host galaxies. We further show that Ly alpha cooling is expected to contribute little to the Ly alpha emission for the majority of emitters. This leaves centrally concentrated star formation at a rate of a few tenths M_sun/yr, surrounded by extended Ly alpha halos with radii up to 30-50 kpc, as the most plausible explanation for the origin of the emission. Both the luminosity function of Ly alpha emission and the velocity width distribution of low ionization absorption require that galaxies inside Dark Matter (DM) halos with virial velocities < 50 - 70 km/s contribute little to the incidence rate of DLAs at z ~ 3, suggesting that energy and momentum input due to star formation efficiently removes gas from these halos. Galaxies with DM halos with virial velocities of 100 - 150 km/s appear to account for the majority of DLA host galaxies. DLA host galaxies at z ~ 3 should thus become the building blocks of typical present-day galaxies.