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Uncovering extremely metal-poor stars in the Milky Way's ultrafaint dwarf spheroidal satellite galaxies

Kirby, Evan N. and Simon, Joshua D. and Geha, Marla and Guhathakurta, Puragra and Frebel, Anna (2008) Uncovering extremely metal-poor stars in the Milky Way's ultrafaint dwarf spheroidal satellite galaxies. Astrophysical Journal, 685 (1). L43-L46. ISSN 0004-637X. doi:10.1086/592432.

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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 V 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.

Item Type:Article
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URLURL TypeDescription Paper
Kirby, Evan N.0000-0001-6196-5162
Geha, Marla0000-0002-7007-9725
Guhathakurta, Puragra0000-0001-8867-4234
Frebel, Anna0000-0002-2139-7145
Additional Information:© 2008 The American Astronomical Society. Received 2008 May 2; accepted 2008 August 13; published 2008 September 5. 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. We thank Jennifer Johnson, Kim Venn, and the referee for valuable advice. We acknowledge National Science Foundation grants AST 03-07966 and AST 06-07852 and NASA/STScI grants GO-10265.02 and GO-10134.02. E. N. K. is supported by a NSF Graduate Research Fellowship. A. F. acknowledges support through the W. J. McDonald Fellowship of the McDonald Observatory.
Funding AgencyGrant Number
NSFAST 03-07966
NSFAST 06-07852
McDonald ObservatoryUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Subject Keywords:galaxies: abundances; galaxies: dwarf
Issue or Number:1
Record Number:CaltechAUTHORS:KIRapjl08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13467
Deposited By: Tony Diaz
Deposited On:02 Apr 2009 19:33
Last Modified:08 Nov 2021 22:38

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