CHEMICAL ENRICHMENT IN THE FAINTEST GALAXIES: THE CARBON AND IRON ABUNDANCE SPREADS IN THE BOOeTES I DWARF SPHEROIDAL GALAXY AND THE SEGUE 1 SYSTEM

Journal Article · Wed Nov 10 04:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/723/2/1632· OSTI ID:21471225

Norris, John E; Yong, David ^[1]; Wyse, Rosemary F. G. ^[2]; Gilmore, Gerard; Belokurov, V; Zucker, Daniel B ^[3]; Frebel, Anna ^[4]

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1. Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611 (Australia)
2. Johns Hopkins University, Department of Physics and Astronomy, 3900 N. Charles Street, Baltimore, MD 21218 (United States)
3. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
4. 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, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 723; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
CARBON
DWARF STARS
ELEMENTS
EVOLUTION
GALACTIC EVOLUTION
GALAXIES
IRON
IRON-DELTA
LUMINOSITY
METALS
MILKY WAY
NONMETALS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIAL VELOCITY
SATELLITES
STAR EVOLUTION
STARS
TRANSITION ELEMENTS
VELOCITY