The First Galaxies and the Likely Discovery of their Fossils in the Local Group
Massimo Ricotti (UMD)

TL;DR
This paper reviews efforts to identify relics of the first galaxies in the Local Group, challenging existing ideas about their star formation history and proposing new mechanisms for their evolution and detection.
Contribution
It introduces a new perspective on the star formation history of first galaxy fossils and suggests they may still form stars or remain dark, contrary to previous beliefs.
Findings
Fossils may have bimodal star formation histories.
Recent gas accretion can trigger star formation in fossils.
Some ultra-faint dwarfs are likely first galaxy fossils.
Abstract
In cold dark matter cosmologies, small mass halos outnumber larger mass halos at any redshift. However, the lower bound for the mass of a galaxy is unknown, as are the typical luminosity of the smallest galaxies and their numbers in the universe. The answers depend on the extent to which star formation in the first population of small mass halos may be suppressed by radiative feedback loops operating over cosmological distance scales. If early populations of dwarf galaxies did form in significant number, their relics should be found today in the Local Group. These relics have been termed "fossils of the first galaxies". This paper is a review that summarizes our ongoing efforts to simulate and identify these fossils around the Milky Way and Andromeda. It is widely believed that reionization of the intergalactic medium would have stopped star formation in the fossils of the first…
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