# Connecting the first galaxies with ultra faint dwarfs in the Local Group: chemical signatures of Population~III stars

## TL;DR

This study uses cosmological simulations to explore the formation, chemical evolution, and star formation history of ultra faint dwarf galaxies, highlighting the role of Population III stars and reionization in shaping their properties.

## Contribution

It provides new insights into the impact of Population III stars and external metal-enrichment on ultra faint dwarf galaxies through detailed cosmological simulations.

## Key findings

- Reionization and supernova feedback truncate star formation in UFDs.
- Population III stars contribute to low-metallicity and CEMP star populations.
- UFDs are assembled from multiple progenitors with diverse star formation histories.

## 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 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.