Scylla: a pure-parallel, multi-headed attack on dust evolution and star formation in ULLYSES galaxies

A precise accounting for interstellar dust is required to interpret the energy output of galaxies. However, our current understanding for how fundamental properties of dust grains vary between interstellar environments is severely limited. Furthermore, our best constraints for how galaxies beyond the Milky Way convert the dusty ISM into stars and planets are based on coarsely-calibrated star formation histories of local systems with unconstrained line-of-sight geometries. To tackle these glaring problems, we propose to conduct a pure-parallel, multi-band imaging program with Wide Field Camera 3 (WFC3) to complement the upcoming Hubble Space Telescope (HST) Ultraviolet (UV) Legacy library of Young Stars as Essential Standards (ULLYSES) survey. ULLYSES will observe massive stars in the Large and Small Magellanic Clouds (LMC, SMC) and other low-metallicity local galaxies. Our multi-band program, Scylla (named after the multi-headed, monstrous foe of Ulysses), will target random parallel fields of ULLYSES targets with WFC3 in photometric bands spanning the UV to the near infrared (NIR). We will: (1) map the extinction curve and dust grain properties at high resolution in a diverse range of interstellar conditions; (2) constrain the multi-dimensional structure of gas in the LMC and SMC; and (3) measure the comprehensive star formation and chemical enrichment histories of nearby dwarf galaxies. The result will be an unprecedented view of star formation in the dusty ISM.