Chemical and stellar properties of early-type dwarf galaxies around the Milky Way

Abstract

Early-type dwarf galaxies (ETDs) are the end-points of the evolution of low-mass galaxies whose gas supplies have been extinguished. The cessation of star formation lays bare the ancient stellar populations. A wealth of information is stored in the colours, magnitudes, metallicities and abundances of resolved stars of the dwarf spheroidal and ultrafaint galaxies around the Milky Way, allowing their chemistry and stellar populations to be studied in great detail. Here we summarize our current understanding, which has advanced rapidly over the past decade owing to flourishing large-scale astrometric, photometric and spectroscopic surveys. We emphasize that the primeval stellar populations in ETDs provide a unique laboratory for studying the physical conditions on small scales at epochs beyond redshift z = 2. We also highlight the observed diversity of star-formation and chemical-enrichment histories in nearby dwarfs. These data cannot yet be fully deciphered to reveal the key processes in dwarf evolution, but the first successful attempts to pin down the sites of heavy-element production have been made.