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Paper: Fossil Signatures of the Reionization Epoch in the Galactic Halo
Volume: 419, Galaxy Evolution: Emerging Insights and Future Challenges
Page: 290
Authors: Madau, P.
Abstract: The Via Lactea II simulation of a Milky Way-sized dark matter halo resolves over 50,000 gravitationally bound clumps orbiting today within the virialized region of the main host. More than 2,000 of these surviving subhalos have one or more “progenitors” with M >106 Msun at redshift z > 11, i.e. massive enough for their gas to have cooled via excitation of H2 and fragmented prior to the epoch of cosmological reionization. If such progenitors were able to convert a fraction of their gas content into very metal-poor stars with a Salpeter initial mass function (IMF), their low-mass stellar populations would still be shining today with a visual magnitude MV = 6.7 per solar mass of initial stars. Assuming a universal baryon fraction, we show that mean star formation efficiencies as low as 0.1% in progenitors << 108 Msun would overproduce the abundance of the faint Galatic dwarf spheroidals observed by the Sloan Digital Sky Survey. Star formation at first light must have occurred either with an IMF lacking stars below 0.9 Msun, or was intrinsically very inefficient in small dark matter halos.
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