The Quenching of the Ultra-Faint Dwarf Galaxies in the Reionization Era

TL;DR

This study investigates the star formation histories of six ultra-faint dwarf galaxies, revealing most stars formed early in cosmic history, supporting the idea that reionization suppressed star formation in small dark matter halos.

Contribution

The paper provides new constraints on the star formation timelines of ultra-faint dwarf galaxies using combined photometry and spectroscopy, highlighting their early formation and reionization effects.

Findings

At least 75% of stars formed by z~10 (13.3 Gyr ago)

80% of stars formed by z~6 (12.8 Gyr ago)

All stars formed by z~3 (11.6 Gyr ago)

Abstract

We present new constraints on the star formation histories of six ultra-faint dwarf galaxies: Bootes I, Canes Venatici II, Coma Berenices, Hercules, Leo IV, and Ursa Major I. Our analysis employs a combination of high-precision photometry obtained with the Advanced Camera for Surveys on the Hubble Space Telescope, medium-resolution spectroscopy obtained with the DEep Imaging Multi-Object Spectrograph on the W.M. Keck Observatory, and updated Victoria-Regina isochrones tailored to the abundance patterns appropriate for these galaxies. The data for five of these Milky Way satellites are best fit by a star formation history where at least 75% of the stars formed by z~10 (13.3 Gyr ago). All of the galaxies are consistent with 80% of the stars forming by z~6 (12.8 Gyr ago) and 100% of the stars forming by z~3 (11.6 Gyr ago). The similarly ancient populations of these galaxies support the hypothesis that star formation in the smallest dark matter sub-halos was suppressed by a global outside influence, such as the reionization of the universe.