2009MNRAS.395L...6S -
Mon. Not. R. Astron. Soc., 395, L6-L10 (2009/May-1)
Ultra faint dwarfs: probing early cosmic star formation.
SALVADORI S. and FERRARA A.
Abstract (from CDS):
We investigate the nature of the newly discovered Ultra Faint dwarf spheroidal galaxies (UF dSphs) in a general cosmological context simultaneously accounting for various `classical' dSphs and Milky Way properties including their metallicity distribution function (MDF). To this aim, we extend the merger tree approach previously developed to include the presence of star-forming minihaloes, and a heuristic prescription for radiative feedback. The model successfully reproduces both the observed [Fe/H]-luminosity relation and the mean MDF of UFs. In this picture, UFs are the oldest, most dark matter-dominated (M/L > 100) dSphs with a total mass M = 107–8M☉; they are leftovers of H2-cooling minihaloes formed at z > 8.5, that is before reionization. Their MDF is broader (because of a more prolonged star formation) and shifted towards lower [Fe/H] (as a result of a lower gas metallicity at the time of formation) than that of classical dSphs. These systems are very ineffectively star-forming, turning into stars by z = 0 only <3 per cent of the potentially available baryons. We provide a useful fit for the star formation efficiency of dSphs.
Abstract Copyright:
© 2009 The Authors. Journal compilation © 2009 RAS
Journal keyword(s):
stars: formation - stars: population II - supernovae: general - galaxies: evolution - cosmology: theory - galaxies: stellar content
Simbad objects:
1
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