Optimizing Time Resolution For Isolated Dwarf Galaxy Star Formation Histories

Star formation histories (SFHs) of dwarf galaxies outside of the Local Group provide a unique view of the evolution of isolated galaxies that are free from the complexities of a group environment. Modeling the age-sensitive features in color-magnitude diagrams (CMDs) of stars resolved in Hubble Space Telescope (HST) imaging is the gold-standard method for measuring SFHs. However, due to the large distances of isolated dwarfs (> 1 Mpc), HST imaging of these galaxies is typically too shallow to reach the oldest stars, resulting in a tradeoff between time resolution and uncertainty in the inferred SFH. In order to find a time binning scheme that minimizes uncertainties, we systematically tested the impact of photometric depth on the ability to recover the star formation activity at different ages using a CMD fitting technique. We created artificial CMDs with realistic photometric uncertainties, then fit the mock data to test whether the input SFH was recovered within the measured uncertainties. The first test was to recover SFHs for mock data generated with identical constant SFHs, while varying the CMD depth from -1.5 to 1.5 in V-band absolute magnitude, spanning the range in our HST imaging dataset for isolated dwarfs. We then tested the impact of starbursts on SFH recovery for fixed CMD depth by fitting mock data generated with a burst of star formation (5x a constant Background SFR) in each age bin. The results of these tests will identify the finest time resolution that ensures accurate recovery of the SFH, given the typical HST data quality for isolated dwarf galaxies. This will enable robust identification of recent starburst events and a better understanding of the impact of starbursts on dwarf galaxy evolution.