The relation between stellar populations, structure and environment for dwarf elliptical galaxies from the MAGPOP-ITP

This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. © 2008 The Authors. Journal compilation © 2008 RAS. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. We would like to thank Scott Trager, Ignacio Trujillo and an anonymous referee for valuable comments and discussion. DM thanks the MAGPOP EU Marie Curie Training and Research Network for financial support. The Network also provided financial support for collaborating research visits during which part of this paper was done. Based on observations made with the NOT, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. The data presented here have been taken using ALFOSC, which is owned by the Instituto de Astrofísica de Andalucía (IAA) and operated at the NOT under agreement between IAA and the NBIfAFG of the Astronomical Observatory of Copenhagen. This paper made use of the following public data bases: SDSS, NED, HyperLEDA, GOLDMine.
Dwarf galaxies, as the most numerous type of galaxy, offer the potential to study galaxy formation and evolution in detail in the nearby universe. Although they seem to be simple systems at first view, they remain poorly understood. In an attempt to alleviate this situation, the MAGPOP EU Research and Training Network embarked on a study of dwarf galaxies named MAGPOP-ITP. In this paper, we present the analysis of a sample of 24 dwarf elliptical galaxies (dEs) in the Virgo cluster and in the field, using optical long-slit spectroscopy. We examine their stellar populations in combination with their light distribution and environment. We confirm and strengthen previous results that dEs are, on average, younger and more metal-poor than normal elliptical galaxies, and that their [alpha/Fe] abundance ratios scatter around solar. This is in accordance with the downsizing picture of galaxy formation where mass is the main driver for the star formation history. We also find new correlations between the luminosity-weighted mean age, the large-scale asymmetry, and the projected Virgocentric distance. We find that environment plays an important role in the termination of the star formation activity by ram-pressure stripping of the gas in short time-scales, and in the transformation of discy dwarfs to more spheroidal objects by harassment over longer time-scales. This points towards a continuing infalling scenario for the evolution of dEs.
MAGPOP EU Marie Curie Training and Research Network
Depto. de Física de la Tierra y Astrofísica
Fac. de Ciencias Físicas
TRUE
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