0 Assigned ID: 605 ----- Attempting Submission 1 (Fri Mar 06 17:59:38 GMT 2020) ----- HST Phase I Proposal 605 successfully submitted. Receipt: # 605-1 ----- Attempting Submission 2 (Fri Mar 06 22:47:17 GMT 2020) ----- Over the past two decades, thousands of HST orbits have been dedicated to measuring the star formation history (SFH) of the Universe. However, the resulting, ubiquitously-used cosmic SFH is only valid for fairly massive galaxies (M_UV < -17) at all redshifts. At low redshift, it neglects the contribution of galaxies less massive than the SMC; at high redshifts, it misses galaxies fainter than Milky Way progenitors. These galaxies are simply too faint to be reliably identified outside of the local Universe. Here, we propose to use archival ACS/WFC3 optical color-magnitude diagrams (CMDs) of 67 Local Group (LG) dwarf galaxies and state-of-the-art cosmological simulations to measure the cosmic SFH of galaxies less massive than the Magellanic Clouds. HST has invested hundreds of orbits in collecting CMDs that reach the oldest main sequence turnoff (MSTO) throughout the LG, enabling the measurement of detailed SFHs back to the reionization era. We will use this rich archival dataset to (1) construct the cosmic SFH for low-mass galaxies and compare it to the widely used high-redshift version; (2) determine the mean-metallicity history of low-mass galaxies; and (3) measure the faint galaxy luminosity and mass functions across cosmic time. For each goal, we will use cosmological simulations to account for completeness, the changing volume of the LG across time, and accretion of dwarf galaxies onto more massive systems (and the subsequent destruction of some of these dwarfs). This archaeological approach in the LG is the only way to measure the cosmic SFH of low-mass galaxies, as they are simply too faint to be detected at the relevant redshifts, even in the JWST-era. Dr. Daniel Weisz is an expert on the resolved stellar populations of low-mass galaxies. He has over worked on over 1500 orbits targeting nearby galaxies, and is author of multiple papers that have measured the star formation histories of nearby dwarf galaxies. Prof. Michael Boylan-Kolchin is a expert in the area of near-field cosmology, including the formation and evolution of the Local Group and dwarf galaxies. He has used simulations of Local Group-like environments to study its formation history, including quantifying it size evolution and how Local Group dwarf galaxies contributed to reionization. Dr. Andrew Dolphin is an expert in resolved star photometry, dwarf galaxies, and measuring star formation histories from color-magnitude diagrams. Stellar Populations and the Interstellar Medium 0 Regular false false false false false SUPPORTED