In "Near-fields cosmology with dwarf elliptical
galaxies", IAU Colloquium Proceedings of the international Astronomical
Union 198, Held 14-18 March, Switzerland, edited by Jerjen, H.;
Binggeli, B. Cambridge: Cambridge University Press, 2005., pp.1-10
For a PDF version of the article, click
here.
astro-ph/0509150
Abstract. The Local Group offers an excellent laboratory for
near-field cosmology by permitting us to use the resolved stellar content
of its constituent galaxies as probes of galaxy formation and evolution,
which in turn is an important means for testing cosmological models of
hierarchical structure formation. In this review, we discuss the the least
massive, yet most
numerous type of galaxy in the Local Group, the dwarf spheroidal galaxies,
and compare their properties to cosmological predictions. In particular,
we point out problems found with a simple building block scenario and with
effects expected from reionization. We show that the star formation
histories of dSphs are inconsistent with the predicted cessation of star
formation after reionization; instead, extended star formation episodes are
observed. The Galactic dSphs contain in part prominent intermediate-age
populations, whereas the Galactic halo does not. Conversely, the M31
dSphs are almost entirely old, while the M31 halo contains a substantial
intermediate-age population. These differences in the population
structure as well as the differences in the modes of star formation
inferred from [
/Fe]
ratios make dSphs unlikely major contributors
to the build-up of the Galactic and M31 halo unless most of the accretion
occurred at early epochs. On the other hand, there
is clear evidence for ongoing harassment and accretion of a number of
dSphs.
keywords galaxies: Local Group, galaxies: dwarf, galaxies: evolution,
galaxies: structure, galaxies: interactions, cosmology: observations,
Galaxy: formation, Galaxy: evolution, stars: late-type, stars: abundances.
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