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26 April 2024 |
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Delving Deeper into the Tumultuous Lives of Galactic Dwarfs: Modeling Star Formation Histories | | Chris Orban
; Oleg Y. Gnedin
; Daniel R. Weisz
; Evan D. Skillman
; Andrew E. Dolphin
; John A. Holtzman
; | | Date: |
7 May 2008 | | Abstract: | The paucity of observed dwarf galaxies in the Local Group and the relative
overabundance of predicted dark matter halos remains one of the greatest
puzzles of the LCDM paradigm. Solving this puzzle now requires not only
matching the numbers of objects but also understanding the details of their
star formation histories. We present a summary of such histories derived from
HST data using the color-magnitude diagram fitting method. We interpret the new
data by using and extending the phenomenological model of Kravtsov, Gnedin &
Klypin (2004), which is based on the mass assembly histories of dark matter
halos and the Kennicutt-Schmidt law of star formation. The model correctly
predicts the radial distributions of dIrr and, separately, dSph galaxy types as
well as the mean age of the stellar populations. However, in order to be
consistent with the observations, the model needs a significant amount of
recent star formation in the last 1 and 2 Gyr. Within the framework of our
extended models, this prolonged star formation can be achieved by adding a
stochastic variation in the density threshold of the star formation law. Our
model results are not sensitive to late gas accretion, the slope of the Schmidt
law, or the details of cosmic reionization. A few discrepancies still remain:
our models typically predict too large total stellar masses and only a modest
population of ultra-faint, low mass dwarfs; additionally our models predict a
small number of dwarfs with anomalously young stellar populations - a problem
which can be solved by removing the simulated dwarfs without star formation in
the first 2 Gyr after the Big Bang. Overall, though, we find that the complex
and extended star formation histories of Local Group dwarfs are generally
consistent with the expected star formation in cold dark matter halos. | | Source: | arXiv, 0805.1058 | | Services: | Forum | Review | PDF | Favorites | |
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