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AR 17560 (Archival Research)

Thu Jul 18 15:03:04 GMT 2024

Principal Investigator: Christopher Garling
PI Institution: The University of Virginia
Investigators (xml)

Title: Probing Patchy Reionization with Uniformly Measured Star Formation Histories of Ultra-Faint Dwarf Galaxies
Cycle: 31

Abstract
HST has been the premier observatory for deriving star formation histories (SFHs) based on resolved stars for the last two decades due to its unique combination of spatial resolution, photometric depth, and wavelength coverage. The resolved color-magnitude diagrams obtained by HST for the ultra-faint dwarf galaxies (M_V > -7; UFDs) of the Milky Way (MW) have indicated these galaxies were quenched around the epoch of reionization, making them fossil remnants of this important cosmological era. However, new SFH measurements of UFDs thought to have fallen into the MW's halo along with the Magellanic Clouds indicate that these UFDs may have been able to form stars for longer than those that were directly accreted onto the MW. This type of variation in SFH could be indicative of local differences in the ultraviolet radiation field during the epoch of reionization and therefore may provide an avenue for constraining models of inhomogeneous reionization. To enable these analyses, we propose to measure the SFHs of the 32 objects observed as part of HST Treasury Proposal 14734. These objects are primarily recently-discovered UFDs with no existing SFH measurements. We will perform a uniform analysis, enabling robust comparisons between SFHs within the sample. We will additionally use the few bright dwarfs in the sample with existing SFH measurements to constrain systematics (i.e., stellar model choice) and enable comparisons to other datasets. The Treasury data reach the oldest main sequence turnoff and were taken in the F606W and F814W filters, known as workhorses for resolved stellar populations -- the data are therefore supremely well-suited to our proposed goal.