Manganese in dwarf spheroidal galaxies^⋆,⋆⋆

¹ Laboratoire d’astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
e-mail: pierre.north@epfl.ch
² Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
³ GEPI, Observatoire de Paris, CNRS, Université de Paris Diderot, 92195 Meudon Cedex, France
⁴ Laboratoire Lagrange, UMR 7293, Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d’Azur, 06300 Nice, France
⁵ McDonald Observatory, University of Texas, Fort Davis, TX 79734, USA
⁶ South African Astronomical Observatory, PO Box 9, 7935 Observatory, South Africa
⁷ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700AV Groningen, The Netherlands
⁸ Dept. of Physics & Astronomy, University of Victoria, 3800 Finerty Road, Victoria, BC V8P 1A1, Canada
⁹ European Southern Observatory, Karl-Schwarzschild-str. 2, 85748 Garching by München, Germany
¹⁰ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

Received: 13 December 2011
Accepted: 1 March 2012

Abstract

We provide manganese abundances (corrected for the effect of the hyperfine structure) for a large number of stars in the dwarf spheroidal galaxies Sculptor and Fornax, and for a smaller number in the Carina and Sextans dSph galaxies. Abundances had already been determined for a number of other elements in these galaxies, including α and iron-peak ones, which allowed us to build [Mn/Fe] and [Mn/α] versus [Fe/H] diagrams. The Mn abundances imply sub-solar [Mn/Fe] ratios for the stars in all four galaxies examined. In Sculptor, [Mn/Fe] stays roughly constant between [Fe/H]  ~  −1.8 and  −1.4 and decreases at higher iron abundance. In Fornax, [Mn/Fe] does not vary in any significant way with [Fe/H]. The relation between [Mn/α] and [Fe/H] for the dSph galaxies is clearly systematically offset from that for the Milky Way, which reflects the different star formation histories of the respective galaxies. The [Mn/α] behavior can be interpreted as a result of the metal-dependent Mn yields of Type II and Type Ia supernovae. We also computed chemical evolution models for star formation histories matching those determined empirically for Sculptor, Fornax, and Carina, and for the Mn yields of SNe Ia, which were assumed to be either constant or variable with metallicity. The observed [Mn/Fe] versus [Fe/H] relation in Sculptor, Fornax, and Carina can be reproduced only by the chemical evolution models that include a metallicity-dependent Mn yield from the SNe Ia.