
TL;DR
This paper models ultra faint dwarf spheroidal galaxies within a cosmological framework, explaining their properties, origins, and relation to early universe minihaloes, and addressing the missing satellites problem.
Contribution
It presents a model that successfully reproduces observed properties of ultra faint dSphs and links them to early universe minihaloes formed before reionization.
Findings
UFs are the oldest and most dark matter-dominated dSphs in the MW.
The model reproduces the observed [Fe/H]-Luminosity relation and MDF.
UF star formation efficiencies are consistent with minihaloes in simulations.
Abstract
We investigate the nature of Ultra Faint dwarf spheroidal galaxies (UF dSphs) in a general cosmological context, simultaneously accounting for various "classical" dSphs and Milky Way (MW) properties, including their Metallicity Distribution Function (MDF). The model successfully reproduces both the observed [Fe/H]-Luminosity relation and the mean MDF of UFs. According to our results UFs are the living fossils of H2-cooling minihaloes formed at z>8.5, i.e. before the end of reionization. They are the oldest and the most dark matter-dominated (M/L > 100) dSphs in the MW system, with a total mass of M = 10^(7-8) Msun. The model allows to interpret the different shape of UFs and classical dSphs MDF, along with the frequency of extremely metal-poor stars in these objects. We discuss the "missing satellites problem" by comparing the UF star formation efficiencies with those derived for…
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