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How do Dwarf Galaxies Acquire Their Mass & When do They Form TheirStars?

Published online by Cambridge University Press:  11 July 2011

M. Koleva ,
Ph. Prugniel ,
I. Vauglin ,
G.A. Mamon ,
D. Tweed ,
A. Cattaneo  and
T.X. Thuan
G.A. Mamon
Affiliation:
Institut d’Astrophysique, Paris, France
D. Tweed
Affiliation:
Institut d’Astrophysique, Paris, France Institut d’Astrophysique Spatiale, Orsay, France
A. Cattaneo
Affiliation:
Astrophysikalisches Institut, Postdam, Germany CRAL, Observatoire de Lyon, Lyon, France
T.X. Thuan
Affiliation:
Dept. of Astronomy, Univ. of Virginia, Charlottesville VA, USA
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Abstract

We apply a simple, one-equation, galaxy formation model on top of the halos and subhalos of a high-resolution dark matter cosmological simulation to study how dwarf galaxies acquire their mass and, for better mass resolution, on over 105 halo merger trees, to predict when they form their stars. With the first approach, we show that the large majority of galaxies within group- and cluster-mass halos have acquired the bulk of their stellar mass through gas accretion and not via galaxy mergers. We deduce that most dwarf ellipticals are not built up by galaxy mergers. With the second approach, we constrain the star formation histories of dwarfs by requiring that star formation must occur within halos of a minimum circular velocity set by the evolution of the temperature of the IGM, starting before the epoch of reionization. We qualitatively reproduce the downsizing trend of greater ages at greater masses and predict an upsizing trend of greater ages as one proceeds to masses lower than mcrit. We find that the fraction of galaxies with very young stellar populations (more than half the mass formed within the last 1.5 Gyr) is a function of present-day mass in stars and cold gas, which peaks at 0.5% at mcrit = 106−8 M⊙, corresponding to blue compact dwarfs such as I Zw 18.

Type
Research Article
Information
European Astronomical Society Publications Series , Volume 48: CRAL-2010 A Universe of Dwarf Galaxies , 2011 , pp. 435 - 440
Copyright
© EAS, EDP Sciences, 2011

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