Star Formation Histories of Ultra-Faint Dwarf Galaxies: environmental differences between Magellanic and non-Magellanic satellites?

TL;DR

This study analyzes the star formation histories of seven ultra-faint dwarf galaxies, revealing that Magellanic satellites tend to quench star formation more recently than other Milky Way satellites, suggesting environmental influence.

Contribution

It provides detailed SFHs of ultra-faint dwarfs and identifies environmental differences between Magellanic and non-Magellanic satellites, highlighting the impact of host environment on galaxy evolution.

Findings

Magellanic satellites have later quenching times by ~600 Myr.

All galaxies formed at least 80% of stars by z~6.

Quenching times are generally older than 11.5 Gyr.

Abstract

We present the color-magnitude diagrams and star formation histories (SFHs) of seven ultra-faint dwarf galaxies: Horologium 1, Hydra 2, Phoenix 2, Reticulum 2, Sagittarius 2, Triangulum 2, and Tucana 2, derived from high-precision Hubble Space Telescope photometry. We find that the SFH of each galaxy is consistent with them having created at least 80% of the stellar mass by $z\sim6$. For all galaxies, we find quenching times older than 11.5 Gyr ago, compatible with the scenario in which reionization suppresses the star formation of small dark matter halos. However, our analysis also reveals some differences in the SFHs of candidate Magellanic Cloud satellites, i.e., galaxies that are likely satellites of the Large Magellanic Cloud and that entered the Milky Way potential only recently. Indeed, Magellanic satellites show quenching times about 600 Myr more recent with respect to those of other Milky Way satellites, on average, even though the respective timings are still compatible within the errors. This finding is consistent with theoretical models that suggest that satellites' SFHs may depend on their host environment at early times, although we caution that within the error bars all galaxies in our sample are consistent with being quenched at a single epoch.