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Title:
Uncovering Extremely Metal-Poor Stars in the Milky Way's Ultrafaint Dwarf Spheroidal Satellite Galaxies
Authors:
Kirby, Evan N.; Simon, Joshua D.; Geha, Marla; Guhathakurta, Puragra; Frebel, Anna
Affiliation:
AA(University of California Observatories/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064; .), AB(Department of Astronomy, California Institute of Technology, 1200 East California Boulevard, MS 105-24, Pasadena, CA 91125.), AC(Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 06520.), AD(University of California Observatories/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064; .), AE(McDonald Observatory, University of Texas, Austin, TX 78712.)
Publication:
The Astrophysical Journal, Volume 685, Issue 1, pp. L43-L46. (ApJ Homepage)
Publication Date:
09/2008
Origin:
UCP
ApJ Keywords:
Galaxies: Abundances, Galaxies: Dwarf
Abstract Copyright:
(c) 2008: The American Astronomical Society
DOI:
10.1086/592432
Bibliographic Code:
2008ApJ...685L..43K

Abstract

We 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. Our 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. Because our [Fe/H] measurements are not tied to empirical metallicity calibrators and are sensitive to arbitrarily low metallicities, we are able to probe this extremely metal-poor regime accurately. The metallicity distribution of stars in these dSphs is similar to the MW halo at the metal-poor end. We also demonstrate that the luminosity-metallicity relation previously seen in more luminous dSph galaxies (MV=-13.4 to -8.8) extends smoothly down to an absolute magnitude of MV=-3.7. The discovery of extremely metal-poor stars in dSphs lends support to the ΛCDM galaxy assembly paradigm wherein dwarf galaxies dissolve to form the stellar halo of the MW.

Data herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

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