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|Title:||Abundance patterns in early-type galaxies: is there a "knee" in the [Fe/H] vs. [α/Fe] relation?||Authors:||Walcher, C. J.
Coelho, P. R. T.
GALLAZZI, Anna Rita
|Issue Date:||2015||Journal:||ASTRONOMY & ASTROPHYSICS||Number:||582||First Page:||A46||Abstract:||Early-type galaxies (ETGs) are known to be enhanced in α elements, in accordance with their old ages and short formation timescales. In this contribution we aim to resolve the enrichment histories of ETGs. This means we study the abundance of Fe ([Fe/H]) and the α-element groups ([α/Fe]) separately for stars older than 9.5 Gyr ([Fe/H]<SUB>o</SUB>, [α/Fe]<SUB>o</SUB>) and for stars between 1.5 and 9.5 Gyr ([Fe/H]<SUB>i</SUB>, [α/Fe]<SUB>i</SUB>). Through extensive simulation we show that we can indeed recover the enrichment history per galaxy. We then analyze a spectroscopic sample of 2286 early-type galaxies from the SDSS selected to be ETGs. We separate out those galaxies for which the abundance of iron in stars grows throughout the lifetime of the galaxy, i.e. in which [Fe/H]<SUB>o</SUB>< [Fe/H]<SUB>i</SUB>. We call those consistent with self-enrichment, while the others must have experienced some mergers or significant gas accretion. We confirm earlier work where the [Fe/H] and [α/Fe] parameters are correlated with the mass and velocity dispersion of ETGs. We emphasize that the strongest relation is between [α/Fe] and age. This relation falls into two regimes, one with a steep slope for old galaxies and one with a shallow slope for younger ETGs. The vast majority of ETGs in our sample do not show the "knee" in the plot of [Fe/H] vs. [α/Fe] commonly observed in local group galaxies. This implies that for the vast majority of ETGs, the stars younger than 9.5 Gyr are likely to have been accreted or formed from accreted gas. The properties of the intermediate-age stars in accretion-dominated ETGs indicate that mass growth through late (minor) mergers in ETGs is dominated by galaxies with low [Fe/H] and low [α/Fe]. The method of reconstructing the stellar enrichment histories of ETGs introduced in this paper promises to constrain the star formation and mass assembly histories of large samples of galaxies in a unique way.||Acknowledgments:||We thank the referee, Alexandre Vazdekis, for a very helpful report, which has helped to significantly improve the presentation of this paper. C.J.W. acknowledges useful discussions with Davor Krajnović, Ivan Minchev, Anne Sansom, Ricardo Schiavon. C.J.W. and P.C. acknowledge support through the Marie Curie Career Integration Grant 303912. S.C. acknowledges support from the European Research Council via an Advanced Grant under grant agreement No. 321323-NEOGAL A.G. acknowledges support from from the European Union FP7/2007-2013 under grant agreement no. 267251 (AstroFIt) and EU Marie Curie Integration Grant “SteMaGE” No. PCIG12-GA-2012-326466 (Call Identifier: FP7-PEOPLE-2012 CIG). Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the US Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web Site is http://www.sdss.org/ . The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.||URI:||http://hdl.handle.net/20.500.12386/23605||URL:||https://arxiv.org/abs/1508.05103
|Appears in Collections:||1.01 Articoli in rivista|
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