Other
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21742402b&link_type=abstract
American Astronomical Society, AAS Meeting #217, #424.02; Bulletin of the American Astronomical Society, Vol. 43, 2011
Other
Scientific paper
We use a new set of cold dark matter simulations of the local universe to investigate the distribution of fossils of primordial dwarf galaxies formed before reionization around the Milky Way. We find good agreement between the observed stellar properties of a subset of the ultra-faint dwarfs and simulated primordial fossils and propose an upper luminosity threshold for fossils of 106 Lsolar. We find the fossils of the first galaxies have galactocentric radial distributions and luminosity functions consistent with observations. In our model, about half of the 200 luminous Milky Way satellites are preserved fossils, with their fraction decreasing with decreasing galactocentric distance and increasing luminosity. Within the Milky Way virial radius, the majority of fossils have luminosities, LV < 104 Lsolar. However, the simulations produce an overabundance of bright dwarf satellites (LV > 104 Lsolar) with respect to observations. This ``bright satellite problem`` is most evident in the outer parts of the Milky Way. We estimate that although relatively bright, the primordial stellar populations in these halos are extremely diffuse, with surface brightness below SDSS detection limits, and easily stripped by tidal forces near the Milky Way. Although we cannot yet present unmistakable evidence of the existence of the fossils of the first galaxies in the Local Group, the results of our studies suggest at least two robust observational strategies that can prove stars did form in minihalos with masses less than 108 Msolar: i) Deep observations toward nearby isolated dwarfs to detect ``ghost halos'' of ancient stars; ii) The detection of another population of 150 Milky Way ultra-faints with 100-1000 pc half-light radii and luminosities LV > 104 Lsolar by future deep surveys. This new population will have minimal trends of stellar velocity dispersion and the maximum circular velocity of the host subhalo with luminosity.
Bovill Mia S.
Ricotti Massimo
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