CHEMICAL ENRICHMENT IN THE FAINTEST GALAXIES: THE CARBON AND IRON ABUNDANCE SPREADS IN THE BOOeTES I DWARF SPHEROIDAL GALAXY AND THE SEGUE 1 SYSTEM
- Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611 (Australia)
- Johns Hopkins University, Department of Physics and Astronomy, 3900 N. Charles Street, Baltimore, MD 21218 (United States)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
We present an AAOmega spectroscopic study of red giants in the ultra-faint dwarf galaxy Booetes I (M{sub V} {approx} -6) and the Segue 1 system (M{sub V} {approx} -1.5), either an extremely low luminosity dwarf galaxy or an unusually extended globular cluster. Both Booetes I and Segue 1 have significant abundance dispersions in iron and carbon. Booetes I has a mean abundance of [Fe/H] = -2.55 {+-} 0.11 with an [Fe/H] dispersion of {sigma} = 0.37 {+-} 0.08, and abundance spreads of {Delta}[Fe/H] = 1.7 and {Delta}[C/H] = 1.5. Segue 1 has a mean of [Fe/H] = -2.7 {+-} 0.4 with [Fe/H] dispersion of {sigma} = 0.7 {+-} 0.3, and abundances spreads of {Delta}[Fe/H] = 1.6 and {Delta}[C/H] = 1.2. Moreover, Segue 1 has a radial-velocity member at four half-light radii that is extremely metal-poor and carbon-rich, with [Fe/H] = -3.5, and [C/Fe] = +2.3. Modulo an unlikely non-member contamination, the [Fe/H] abundance dispersion confirms Segue 1 as the least-luminous ultra-faint dwarf galaxy known. For [Fe/H] < -3.0, stars in the Milky Way's dwarf galaxy satellites exhibit a dependence of [C/Fe] on [Fe/H] similar to that in Galactic field halo stars. Thus, chemical evolution proceeded similarly in the formation sites of the Galaxy's extremely metal-poor halo stars and in the ultra-faint dwarf galaxies. We confirm the correlation between (decreasing) luminosity and both (decreasing) mean metallicity and (increasing) abundance dispersion in the Milky Way dwarf galaxies at least as faint as M{sub V} = -5. The very low mean iron abundances and the high carbon and iron abundance dispersions in Segue 1 and Booetes I are consistent with highly inhomogeneous chemical evolution starting in near zero-abundance gas. These ultra-faint dwarf galaxies are apparently surviving examples of the very first bound systems.
- OSTI ID:
- 21471225
- Journal Information:
- Astrophysical Journal, Vol. 723, Issue 2; Other Information: DOI: 10.1088/0004-637X/723/2/1632; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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