Revealing the Cosmic Build-up of Interstellar Dust with Space Telescopes - The Nearby Universe as a Laboratory
Julia Roman-Duval (Space Telescope Science Institute)

Variations in the abundance of interstellar dust have important implications for our ability to trace the chemical enrichment of the universe, stellar mass assembly, and profoundly affect galaxy evolution. I will present results from three observational efforts to characterize the variations of the dust content and properties within and between galaxies, in particular as a function of metallicity and gas density. The dust and gas contents of nearby galaxies were measured using far-infrared, HI 21 cm, and CO emission on the one hand, and UV absorption spectroscopy with Hubble on the other hand. Both approaches demonstrate a significant increase of the dust abundance with gas density, even in very low metallicity systems such as Sextans A (7% solar metallicity). Furthermore, the fraction of metals locked in dust decreases with decreasing metallicity, by a factor of 2 from the Milky Way to the SMC, and a factor 4 from the Milky Way to Sextans A. This results in the dust-to-gas ratio (D/G) decreasing faster than metallicity, consistent with chemical evolution models and with measurements in Damped Lyman-alpha systems at redshift <4. However, this decrease in D/G is not as dramatic as suggested from previous FIR measurements in nearby galaxies. Furthermore, ongoing efforts to measure the properties and abundance of the smallest dust grains, polycyclic aromatic hydrocarbons (PAHs), in very low metallicity systems with JWST are revealing that PAHs do exist in those environments, but were previously missed owing to the very small size (pc-scale) of the dense regions in which they can form and survive.

The agenda will be shared with the Teams link as we get closer to the event. Actual start time is 3:10 p.m.

Local Dwarf Galaxies as Laboratories to Understand Massive Stars and the ISM in the Early Universe
Grace Telford (Princeton University)

Feedback from low-metallicity massive stars regulates the evolution of both dwarf and high-redshift galaxies. To understand those processes requires robust models of the metal-poor ISM in which stars form and of massive stars' winds and ionizing spectra. Yet, these models remain entirely theoretical and uncertain due to a lack of observational constraints in the extremely low-metallicity regime. In this talk, I will present a suite of JWST, HST, and Keck observations of the nearby 3% Solar metallicity galaxy Leo P. First, I will describe novel constraints on the wind properties and ionizing spectrum of the galaxy's only O-type star from modeling HST/COS and Keck/KCWI spectroscopy. This star is part of the Treasury of Extremely Metal-Poor O Stars (TEMPOS), a Large Treasury HST program that will extend this initial analysis to a much larger sample at ~5-10% Solar metallicity. I will then present new JWST/MIRI-MRS observations of Leo P, which enabled the first detection of cold molecular hydrogen at such low metallicity via rotationally excited emission from the photodissociation region illuminated by the O star. Our detailed understanding of that star's UV radiation from the HST data constrains the temperature and mass of the detected molecular hydrogen, providing a benchmark for models of the ISM at the very low metallicities typical at high redshift. Leo P showcases the potential of the metal-poor dwarf galaxies in our backyard to inform models of early galaxies.