Volume 501, Number 1, July I 2009
|Page(s)||189 - 206|
|Published online||05 May 2009|
The dynamical and chemical evolution of dwarf spheroidal galaxies*
Laboratoire d'Astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), 1290 Sauverny, Switzerland e-mail: email@example.com
2 University of Geneva, Observatory, 1290 Sauverny, Switzerland; on leave from CNRS, UMR 8111
3 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, 85748 Garching bei München, Germany
4 Observatoire de la Côte d'Azur, CNRS UMR 6202, BP 4229, 06304 Nice Cedex 4, France
5 California Institute of Technology, MC105-24, Pasadena, CA 91125, USA
6 Institute of Astronomy, Madingley Road, Cambridge CB03 0HA, UK
7 European Southern Observatory, Karl-Schwarzschild-Straße 1, 85748 Garching bei München, Germany
8 Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
9 McDonald Observatory, University of Texas, Fort Davis, TX 79734, USA
10 Department of Physics & Astronomy, University of Victoria, Elliott Building, 3800 Finnerty Road, Victoria, BC, V8P 5C2, Canada
Accepted: 17 April 2009
We present a large sample of fully self-consistent hydrodynamical Nbody/Tree-SPH simulations of isolated dwarf spheroidal galaxies (dSphs). It has enabled us to identify the key physical parameters and mechanisms at the origin of the observed variety in the Local Group dSph properties. The initial total mass (gas + dark matter) of these galaxies is the main driver of their evolution. Star formation (SF) occurs in series of short bursts. In massive systems, the very short intervals between the SF peaks mimic a continuous star formation rate, while less massive systems exhibit well separated SF bursts, as identified observationally. The delay between the SF events is controlled by the gas cooling time dependence on galaxy mass. The observed global scaling relations, luminosity-mass and luminosity-metallicity, are reproduced with low scatter. We take advantage of the unprecedentedly large sample size and data homogeneity of the ESO Large Programme DART, and add to it a few independent studies, to constrain the star formation history of five Milky Way dSphs, Sextans, LeoII, Carina, Sculptor and Fornax. For the first time, [Mg/Fe] vs. [Fe/H] diagrams derived from high-resolution spectroscopy of hundreds of individual stars are confronted with model predictions. We find that the diversity in dSph properties may well result from intrinsic evolution. We note, however, that the presence of gas in the final state of our simulations, of the order of what is observed in dwarf irregulars, calls for removal by external processes.
Key words: galaxies: dwarf / galaxies: evolution / galaxies: formation
© ESO, 2009
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