MULTI-ELEMENT ABUNDANCE MEASUREMENTS FROM MEDIUM-RESOLUTION SPECTRA. III. METALLICITY DISTRIBUTIONS OF MILKY WAY DWARF SATELLITE GALAXIES

Abstract

We present metallicity distribution functions (MDFs) for the central regions\nof eight dwarf satellite galaxies of the Milky Way: Fornax, Leo I and II,\nSculptor, Sextans, Draco, Canes Venatici I, and Ursa Minor. We use the\npublished catalog of abundance measurements from the previous paper in this\nseries. The measurements are based on spectral synthesis of iron absorption\nlines. For each MDF, we determine maximum likelihood fits for Leaky Box,\nPre-Enriched, and Extra Gas (wherein the gas supply available for star\nformation increases before it decreases to zero) analytic models of chemical\nevolution. Although the models are too simplistic to describe any MDF in\ndetail, a Leaky Box starting from zero metallicity gas fits none of the\ngalaxies except Canes Venatici I well. The MDFs of some galaxies, particularly\nthe more luminous ones, strongly prefer the Extra Gas Model to the other\nmodels. Only for Canes Venatici I does the Pre-Enriched Model fit significantly\nbetter than the Extra Gas Model. The best-fit effective yields of the less\nluminous half of our galaxy sample do not exceed 0.02 Z_sun, indicating that\ngas outflow is important in the chemical evolution of the less luminous\ngalaxies. We surmise that the ratio of the importance of gas infall to gas\noutflow increases with galaxy luminosity. Strong correlations of average [Fe/H]\nand metallicity spread with luminosity support this hypothesis.\n