Damped Lyman Alpha Systems in Galaxy Formation Simulations

TL;DR

This study uses high-resolution galaxy formation simulations to accurately reproduce the properties of damped Lyman alpha systems at z=3, providing insights into their role in galaxy evolution without parameter tuning.

Contribution

First simulations to match observed DLA metallicity distribution and incidence rate without relying on unsupported mechanisms, validating the realism of galaxy formation models.

Findings

Simulations closely match observed DLA incidence and column density distributions.

Reproduce DLA metallicity distribution with median Z_{DLA} = Z_{solar}/20.

Underestimate high velocity width systems, similar to other studies.

Abstract

We investigate the population of z=3 damped Lyman alpha absorbers (DLAs) in a recent series of high resolution galaxy formation simulations. The simulations are of interest because they form at z=0 some of the most realistic disk galaxies to date. No free parameters are available in our study: these have been fixed by physical and z=0 observational constraints, and thus our study provides a genuine consistency test. The precise role of DLAs in galaxy formation remains in debate, but they provide a number of strong constraints on the nature of our simulated bound systems at z=3 because of their coupled information on neutral H I densities, kinematics, metallicity and estimates of star formation activity. Our results, without any parameter-tuning, closely match the observed incidence rate and column density distributions of DLAs. Our simulations are the first to reproduce the distribution of metallicities (with a median of Z_{DLA} = Z_{solar}/20) without invoking observationally unsupported mechanisms such as dust biasing. This is especially encouraging given that these simulations have previously been shown to have a realistic 0<z<2 stellar mass-metallicity relation. Additionally, we see a strong positive correlation between sightline metallicity and low-ion velocity width, the normalization and slope of which comes close to matching recent observational results. However, we somewhat underestimate the number of observed high velocity width systems; the severity of this disagreement is comparable to other recent DLA focused studies. By z=0 the majority of the z=3 neutral gas forming the DLAs has been converted into stars, in agreement with rough physical expectations. [Abridged]