Simulating High-Redshift Disk Galaxies: Applications to Long Duration Gamma-Ray Burst Hosts

TL;DR

This study uses hydrodynamical simulations to explore how star formation efficiency and molecular hydrogen influence high-redshift galaxy properties, especially those hosting long-duration gamma-ray bursts, revealing insights into their molecular ISM and star formation rates.

Contribution

It demonstrates that hydrodynamical simulations can reproduce observed properties of high-redshift GRB host galaxies, highlighting the role of molecular ISM in their star formation.

Findings

Simulations match observed star formation rates of GRB hosts at z~1-2.

GRB host galaxies may have higher molecular hydrogen fractions than observed in sightlines.

Compact high-redshift low-mass galaxies can have significant molecular ISM fractions.

Abstract

The efficiency of star formation governs many observable properties of the cosmological galaxy population, yet many current models of galaxy formation largely ignore the important physics of star formation and the interstellar medium (ISM). Using hydrodynamical simulations of disk galaxies that include a treatment of the molecular ISM and star formation in molecular clouds (Robertson & Kravtsov 2008), we study the influence of star formation efficiency and molecular hydrogen abundance on the properties of high-redshift galaxy populations. In this work, we focus on a model of low-mass, star forming galaxies at 1<~z<~2 that may host long duration gamma-ray bursts (GRBs). Observations of GRB hosts have revealed a population of faint systems with star formation properties that often differ from Lyman-break galaxies (LBGs) and more luminous high-redshift field galaxies. Observed GRB sightlines are deficient in molecular hydrogen, but it is unclear to what degree this deficiency owes to intrinsic properties of the galaxy or the impact the GRB has on its environment. We find that hydrodynamical simulations of low-stellar mass systems at high-redshifts can reproduce the observed star formation rates and efficiencies of GRB host galaxies at redshifts 1<~z<~2. We show that the compact structure of low-mass high-redshift GRB hosts may lead to a molecular ISM fraction of a few tenths, well above that observed in individual GRB sightlines. However, the star formation rates of observed GRB host galaxies imply molecular gas masses of 10^8 - 10^9 M_sun similar to those produced in the simulations, and may therefore imply fairly large average H_2 fractions in their ISM.