Evan Kirby (UC Santa Cruz)

Title: Discovery of Extremely Metal-Poor Stars in the Ultra-Faint Dwarf Spheroidal Galaxies of the Milky Way

Abstract: I present new metallicity measurements for 298 individual red giant branch stars in eight of the least luminous dwarf spheroidal galaxies (dSphs) in the Milky Way (MW) system. My technique is based on medium resolution Keck/DEIMOS spectroscopy coupled with spectral synthesis. We present the first spectroscopic metallicities at [Fe/H] < -3.0 of stars in a dwarf galaxy, with individual stellar metallicities as low as [Fe/H] = -3.3. The metallicity distribution of stars in these dSphs is similar to the MW halo at the metal-poor end. I also demonstrate that the luminosity-metallicity relation previously seen in more luminous dSph galaxies (M_V = -13.4 to -8.8) extends smoothly down to an absolute magnitude of M_V = -3.7. For more information, please visit http://arxiv.org/abs/0807.1925. I will also show very new metallicity distributions for larger dSphs (Sculptor and Fornax) from DEIMOS data taken on Aug 30-31.