The SPLASH Survey: Milky Way vs. M 31 dSphs

¹ STScI, 3700 San Martin Drive, Baltimore, MD 21218, USA
² Department of Astronomy, University of Virginia, PO Box 3818, Charlottesville, VA 22903, USA
³ Astronomy Department, Yale University, New Haven, CT 06510, USA
⁴ Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195, USA
⁵ UCO/Lick, Astronomy, UCSC, 1156 High Street, Santa Cruz, CA 95064, USA
⁶ Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
⁷ Center for Cosmology, Department of Physics and Astronomy, University of California at Irvine, Irvine, CA 92697, USA

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Abstract

We present the first systematic comparison of the detailed properties, including internal kinematics, chemical abundances, sizes, and dark matter masses, of Milky Way and M 31 dSphs as a part of the SPLASH Survey (Spectroscopic and Photometric Landscape of Andromeda’s Stellar Halo). Through Keck/DEIMOS spectroscopy of several hundred individual red giants in a half dozen M 31 galaxies, our results indicate both similarities and differences between the family of dSphs in the Milky Way and M 31. For example, we find that the luminosity-metallicity relation of dSphs in the two hosts is very similar between L = 10⁵ and 10⁷ L_⊙, the size distribution of M 31 dSphs extends to larger values at the same luminosity compared to Milky Way counterparts (especially at the bright end), and that the dark matter masses of M 31 dSphs are slightly smaller than similar luminosity Milky Way galaxies.