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The Distribution of Alpha Elements in Ultra-Faint Dwarf Galaxies

Vargas, Luis C. and Geha, Marla and Kirby, Evan N. and Simon, Joshua D. (2013) The Distribution of Alpha Elements in Ultra-Faint Dwarf Galaxies. Astrophysical Journal, 767 (2). Art. No. 134. ISSN 0004-637X. doi:10.1088/0004-637x/767/2/134.

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The Milky Way ultra-faint dwarf (UFD) galaxies contain some of the oldest, most metal-poor stars in the universe. We present [Mg/Fe], [Si/Fe], [Ca/Fe], [Ti/Fe], and mean [α/Fe] abundance ratios for 61 individual red giant branch stars across eight UFDs. This is the largest sample of alpha abundances published to date in galaxies with absolute magnitudes M_V > –8, including the first measurements for Segue 1, Canes Venatici II, Ursa Major I, and Leo T. Abundances were determined via medium-resolution Keck/DEIMOS spectroscopy and spectral synthesis. The sample spans the metallicity range –3.4 <[Fe/H] < –1.1. With the possible exception of Segue 1 and Ursa Major II, the individual UFDs show on average lower [α/Fe] at higher metallicities, consistent with enrichment from Type Ia supernovae. Thus, even the faintest galaxies have undergone at least a limited level of chemical self-enrichment. Together with recent photometric studies, this suggests that star formation in the UFDs was not a single burst, but instead lasted at least as much as the minimum time delay of the onset of Type Ia supernovae (~100 Myr) and less than ~2 Gyr. We further show that the combined population of UFDs has an [α/Fe] abundance pattern that is inconsistent with a flat, Galactic halo-like alpha abundance trend, and is also qualitatively different from that of the more luminous CVn I dSph, which does show a hint of a plateau at very low [Fe/H].

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Vargas, Luis C.0000-0001-7155-0040
Geha, Marla0000-0002-7007-9725
Kirby, Evan N.0000-0001-6196-5162
Additional Information:© 2013 The American Astronomical Society. Received 2012 December 11; accepted 2013 March 1; published 2013 April 4. The authors would like to thank Ana Bonaca and the anonymous referee for helpful comments on the manuscript. L.C.V. is supported by an NSF Graduate Research Fellowship. M.G. acknowledges support from NSF grant AST-0908752 and the Alfred P. Sloan Foundation. E.N.K. acknowledges support from the Southern California Center for Galaxy Evolution, a multicampus research program funded by the University of California Office of Research, and partial support from NSF grant AST-1009973. We wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Funding AgencyGrant Number
NSF Graduate Research FellowshipUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Southern California Center for Galaxy EvolutionUNSPECIFIED
University of CaliforniaUNSPECIFIED
Subject Keywords:galaxies: abundances – galaxies: dwarf – galaxies: evolution – Local Group
Issue or Number:2
Record Number:CaltechAUTHORS:20190514-105618815
Persistent URL:
Official Citation:Luis C. Vargas et al 2013 ApJ 767 134
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95484
Deposited By: Tony Diaz
Deposited On:14 May 2019 20:49
Last Modified:16 Nov 2021 17:13

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