Complexity in small-scale dwarf spheroidal galaxies

TL;DR

This paper reviews the complex chemical evolution of ultrafaint dwarf spheroidal galaxies, highlighting their inhomogeneous enrichment, presence of extremely metal-poor stars, and potential contribution to the Milky Way's metal-poor halo.

Contribution

It provides a synthesis of recent high-resolution abundance analyses of ultrafaint dSphs and discusses their role in Galactic halo formation.

Findings

Ultrafaint dSphs show highly inhomogeneous chemical enrichment.

Presence of stars with [Fe/H] < -3 dex suggests early star formation.

Some ultrafaint dSphs may have contributed to the metal-poor Galactic halo.

Abstract

Our knowledge about the chemical evolution of the more luminous dwarf spheroidal (dSph) galaxies is constantly growing. However, little is known about the enrichment of the ultrafaint systems recently discovered in large numbers in large Sky Surveys. Low-resolution spectroscopy and photometric data indicate that these galaxies are predominantly metal-poor. On the other hand, the most recent high-resolution abundance analyses indicate that some of these galaxies experienced highly inhomogenous chemical enrichment, where star formation proceeds locally on the smallest scales. Furthermore, these galaxy-contenders appear to contain very metal-poor stars with [Fe/H]<-3 dex and could be the sites of the first stars. Here, we consider the presently available chemical abundance information of the (ultra-) faint Milky Way satellite dSphs. In this context, some of the most peculiar element and inhomogeneous enrichment patterns will be discussed and related to the question of to what extent the faintest dSph candidates and outer halo globular clusters could have contributed to the metal-poor Galactic halo.