Beschreibung
A galaxy's mean metallicity is usually closely correlated with its luminosity and mass. Consequently the most metal-poor galaxies in the local universe are dwarf galaxies. Late-type dwarf galaxies tend to have experienced low-efficiency, fairly continuous star formation since a Hubble time with amplitude variations of up to a factor of three. Early-type dwarf galaxies are dominated by old and intermediate-age stellar populations while having little gas and typically no active star formation at the present time. This class of objects includes the least luminous, least massive galaxies known - the very metal-deficient, old ultra-faint dwarf spheroidal galaxies that were recently discovered around the Milky Way. Both classes contribute to the build-up of more massive galaxies, albeit in different ways.
