Multi-element Abundance Measurements from Medium-resolution Spectra. III. Metallicity Distributions of Milky Way Dwarf Satellite Galaxies
We present metallicity distribution functions (MDFs) for the central regions of eight dwarf satellite galaxies of the Milky Way: Fornax, Leo I and II, Sculptor, Sextans, Draco, Canes Venatici I, and Ursa Minor. We use the published catalog of abundance measurements from the previous paper in this series. The measurements are based on spectral synthesis of iron absorption lines. For each MDF, we determine maximum likelihood fits for Leaky Box, Pre-Enriched, and Extra Gas (wherein the gas supply available for star formation increases before it decreases to zero) analytic models of chemical evolution. Although the models are too simplistic to describe any MDF in detail, a Leaky Box starting from zero metallicity gas fits none of the galaxies except Canes Venatici I well. The MDFs of some galaxies, particularly the more luminous ones, strongly prefer the Extra Gas Model to the other models. Only for Canes Venatici I does the Pre-Enriched Model fit significantly better than the Extra Gas Model. The best-fit effective yields of the less luminous half of our galaxy sample do not exceed 0.02Z_⊙, indicating that gas outflow is important in the chemical evolution of the less luminous galaxies. We surmise that the ratio of the importance of gas infall to gas outflow increases with galaxy luminosity. Strong correlations of average [Fe/H] and metallicity spread with luminosity support this hypothesis.
Additional Information© 2011 American Astronomical Society. Received 2010 May 12; accepted 2010 November 7; published 2011 January 5. We thank the anonymous referee for helpful advice that improved this manuscript. We also thank Bob Kraft for helpful comments and Julianne Dalcanton for the suggestion that gas may become available for SF in ways other than the infall of external gas. We also recognize the work of Marla Geha, Steve Majewski, Connie Rockosi, Michael Siegel, Chris Sneden, Tony Sohn, and Peter Stetson in making the data catalog used in this article possible. Support for this work was provided by NASA through Hubble Fellowship grant HST-HF-51256.01 awarded to E.N.K. by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. G.A.L. acknowledges financial support from the Brazilian agency FAPESP (proj. 06/57824-1). NSF grant AST-0908139, awarded to J.G.C., provided partial support for this project. P.G. acknowledges NSF grants AST-0307966, AST-0607852, and AST-0507483. The authors 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.
Published - Kirby2011p12849Astrophys_J.pdf
Accepted Version - 1011.4937.pdf
Erratum - Kirby2012p18282Astrophys_J.pdf