The Faint Optical Stellar Luminosity Function in the Ursa Minor Dwarf Spheroidal Galaxy

摘要

Analyses of their internal stellar kinematics imply that the dwarf spheroidal(dSph) companion galaxies to the Milky Way are among the most dark-matterdominated systems known. Should there be significant dark matter in the form offaint stars in these systems, the stellar luminosity function must be verydifferent from that of a similar metallicity globular cluster, for which thereis no evidence for dark matter. We present the faint stellar luminosityfunction in the Ursa Minor dSph, down to a luminosity corresponding to roughly0.45 M_sun, derived from new deep HST/WFPC2 data. We find a remarkablesimilarity between this luminosity function, and inferred initial massfunction, and that of the globular cluster M92, a cluster of similar age andmetallicity to the Ursa Minor dSph.