First stars in Damped Lyman Alpha systems

TL;DR

This paper introduces a new model linking Damped Lyman Alpha systems with first stars, explaining their chemical properties and evolution within the Milky Way formation context, including the discovery of a new class of PopIII DLAs.

Contribution

It extends the merger tree method to include inhomogeneous reionization and metal mixing, providing a novel framework to study first stars in DLAs and their connection to metal-poor stars and dwarf galaxies.

Findings

The model matches observed metallicity and Fe relations in DLAs.

Identification of a new class of PopIII DLAs hosting first stars.

Explanation of the properties of recently discovered C-enhanced DLAs.

Abstract

In order to characterize Damped Lyman Alpha systems (DLAs) potentially hosting first stars, we present a novel approach to investigate DLAs in the context of Milky Way (MW) formation, along with their connection with the most metal-poor stars and local dwarf spheroidal (dSph) galaxies. The merger tree method previously developed is extended to include inhomogeneous reionization and metal mixing, and it is validated by matching both the Metallicity Distribution Function of Galactic halo stars and the Fe-Luminosity relation of dSph galaxies. The model explains the observed NHI-Fe relation of DLAs along with the chemical abundances of [Fe/H] < -2 systems. In this picture, the recently discovered z_abs ~ 2.34 C-enhanced DLA (Cooke et al. 2011a), pertains to a new class of absorbers hosting first stars along with second-generation long-living low-mass stars. These "PopIII DLAs" are the descendants of H2-cooling minihalos with Mh ~ 10^7 Msun, that virialize at z > 8 in neutral, primordial regions of the MW environment and passively evolve after a short initial period of star formation. The gas in these systems is warm Tg \sim (40-1000) K, and strongly C-enriched by long-living, extremely metal-poor stars of total mass M* \sim 10^{2-4} Msun.