Chemical enrichment in very low metallicity environments: Boötes I

Abstract

We present different chemical evolution models for the ultrafaint dwarf galaxy Boötes I. We either assume that the galaxy accretes its mass through smooth infall of gas of primordial chemical composition (classical models) or adopt mass accretion histories derived from the combination of merger trees with semi-analytical modelling (cosmologically-motivated models). Furthermore, we consider models with and without taking into account inhomogeneous mixing in the interstellar medium within the galaxy, i.e. homogeneous versus inhomogeneous models. The theoretical predictions are then compared to each other and to the body of the available data. From this analysis, we confirm previous findings that Boötes I has formed stars with very low efficiency but, at variance with previous studies, we do not find a clear-cut indication that supernova explosions have sustained long-lasting galactic-scale outflows in this galaxy. Therefore, we suggest that external mechanisms such as ram pressure stripping and tidal stripping are needed to explain the absence of neutral gas in Boötes I today.