Connecting the first galaxies with ultra faint dwarfs in the Local
  Group: chemical signatures of Population~III stars
  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 10^2 solar mass < M_star <10^5 solar mass) and gas rich, low mass
dwarfs (Leo P analogs; stellar mass range of 10^5 solar mass < M_star <10^6
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 M_vir < 2 x 10^9 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
$\rm [C/Fe]$ yields, and the associated external metal-enrichment, in producing
low-metallicity stars ($\rm [Fe/H]\lesssim-4$) 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 M_vir ~ 4 x 10^9 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.
