Connecting the first galaxies with ultra faint dwarfs in the Local Group: chemical signatures of Population~III stars
Abstract
We investigate the star formation history and chemical evolution of isolated analogues of Local Group (LG) ultra faint dwarf galaxies (UFDs; stellar mass range of 102 solar mass < Mstar <105 solar mass) and gas rich, low mass dwarfs (Leo P analogs; stellar mass range of 105 solar mass < Mstar <106 solar mass). We perform a suite of cosmological hydrodynamic zoom-in simulations to follow their evolution from the era of the first generation of stars down to z=0. We confirm that reionization, combined with supernova (SN) feedback, is primarily responsible for the truncated star formation in UFDs. Specifically, haloes with a virial mass of Mvir < 2 x 109 solar mass form> 90\% of stars prior to reionization. Our work further demonstrates the importance of Population~III (Pop~III) stars, with their intrinsically high [C/Fe] yields, and the associated external metal-enrichment, in producing low-metallicity stars ( [Fe/H]-4) and carbon-enhanced metal-poor (CEMP) stars. We find that UFDs are composite systems, assembled from multiple progenitor haloes, some of which hosted only Population~II (Pop~II) stars formed in environments externally enriched by SNe in neighboring haloes, naturally producing, extremely low-metallicity Pop~II stars. We illustrate how the simulated chemical enrichment may be used to constrain the star formation histories (SFHs) of true observed UFDs. We find that Leo P analogs can form in haloes with Mvir ~ 4 x 109 solar mass (z=0). Such systems are less affected by reionization and continue to form stars until z=0, causing higher metallicity tails. Finally, we predict the existence of extremely low-metallicity stars in LG UFD galaxies that preserve the pure chemical signatures of Pop~III nucleosynthesis.