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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 fromhigh-precision Hubble Space Telescope photometry. We find that the SFH of eachgalaxy is consistent with them having created at least 80% of the stellar massby $z\sim6$. For all galaxies, we find quenching times older than 11.5 Gyr ago,compatible with the scenario in which reionization suppresses the starformation of small dark matter halos. However, our analysis also reveals somedifferences in the SFHs of candidate Magellanic Cloud satellites, i.e.,galaxies that are likely satellites of the Large Magellanic Cloud and thatentered the Milky Way potential only recently. Indeed, Magellanic satellitesshow quenching times about 600 Myr more recent with respect to those of otherMilky Way satellites, on average, even though the respective timings are stillcompatible within the errors. This finding is consistent with theoreticalmodels that suggest that satellites' SFHs may depend on their host environmentat early times, although we caution that within the error bars all galaxies inour sample are consistent with being quenched at a single epoch.

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