Ultrafaint Dwarfs - Star Formation and Chemical Evolution in the Smallest Galaxies

TL;DR

This study investigates star formation and chemical evolution in ultrafaint dwarf galaxies with a virial mass of 10^7 solar masses, highlighting the effects of supernova explosions and gas retention on their development.

Contribution

It extends previous work by modeling multiple star formation episodes and analyzing the impact of supernova explosion locations on gas retention and chemical enrichment.

Findings

Central supernova explosions have a stronger impact on gas loss and enrichment.

Off-centered supernovae allow most metals to escape into the IGM.

Models can reproduce observed [$\alpha$/Fe] and [Fe/H] relationships in ultra-faint dwarfs.

Abstract

In earlier work we showed that a dark matter halo with a virial mass of $10^7$ M$_\odot$ can retain a large percentage of its baryons in the face of the pre-ionization phase and supernova explosion from a 25$M_\odot$ star. Here we expand on the results of that work, investigating the star formation and chemical evolution of the system beyond the first supernova. In a galaxy with a mass $M_{vir} = 10^7$M$_\odot$, sufficient gas is retained by the potential for a second period of star formation to occur. The impact of a central explosion is found to be much stronger than that of an off-centred explosion both in blowing out the gas and in enriching it, as in the off-centered case most of the supernova energy and metals escape into the IGM. We model the star formation and metallicity given the assumption that stars form for 100, 200, 400 and 600 Myr and discuss the results in the context of recent observations of very low mass galaxies. We show that we can account for most features of the observed relationship between [$\alpha$/Fe] and [Fe/H] in ultra-faint dwarf galaxies with the assumption that the systems formed at a low mass, rather than being remnants of much larger systems.