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Seminar: Wednesday, November 12, 2008 at 3:30pm

Fossils of the first galaxies in the Local Group and the role of reionization feedback on suppressing the formation of dwarf galaxies
Massimo Ricotti
Department of Astronomy
University of Maryland College Park

In this talk I show results of cosmological simulations suggesting a possible identification of at least some dwarf spheroidal galaxies in the Local Group as the fossils of the first galaxies (``pre-reionization fossils''). I also revisit the problem of gas accretion onto minihalos after reionization. I show that primordial minihalos with v_{cir}<20 km/s stop accreting gas after reionization, as it is usually assumed, but in virtue of their increasing concentration and the decreasing temperature of the intergalactic medium as redshift decreases, they may have a late phase (at redshift z<2) of gas accretion and possibly star formation. As a result we expect that pre-reionization fossils have a more complex star formation history than previously envisioned. The dwarf spheroidal galaxy Leo~T fits with this scenario. Another prediction of the model is the existence of a population of gas rich minihalos that never formed stars. A subset of compact high-velocity clouds may be identified as such objects but the bulk of them may still be undiscovered.

Location: Physics Bldg., Room 401