The Star Formation History of Leo T from Hubble Space Telescope Imaging
Daniel R. Weisz, Daniel B. Zucker, Andrew E. Dolphin, Nicolas F., Martin, Jelte T. A. de Jong, Jon A. Holtzman, Julianne J. Dalcanton, Karoline, M. Gilbert, Benjamin F. Williams, Eric F. Bell, Vasily Belokurov, N. Wyn, Evans

TL;DR
This paper reconstructs the detailed star formation history of Leo T, the faintest known star-forming galaxy, using deep HST imaging, revealing a significant early star formation epoch and recent activity decline, with implications for dwarf galaxy evolution.
Contribution
It provides the first high-resolution, model-robust star formation history of Leo T, highlighting its similarities to gas-rich dwarf galaxies and improving understanding of low-mass galaxy evolution.
Findings
50% of stars formed before z ~ 1 (7.6 Gyr ago)
Star formation remained roughly constant until ~25 Myr ago
Leo T's properties resemble gas-rich dwarf galaxies rather than typical faint dwarfs.
Abstract
We present the star formation history (SFH) of the faintest known star-forming galaxy, Leo T, based on imaging taken with the Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2). The HST/WFPC2 color-magnitude diagram (CMD) of Leo T is exquisitely deep, extending ~ 2 magnitudes below the oldest main sequence turnoff, permitting excellent constraints on star formation at all ages. We use a maximum likelihood CMD fitting technique to measure the SFH of Leo T assuming three different sets of stellar evolution models: Padova (solar-scaled metallicity) and BaSTI (both solar-scaled and alpha-enhanced metallicities). The resulting SFHs are remarkably consistent at all ages, indicating that our derived SFH is robust to the choice of stellar evolution model. From the lifetime SFH of Leo T, we find that 50% of the total stellar mass formed prior to z ~ 1 (7.6 Gyr ago). Subsequent to…
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