CTC Seminar for 2022-11-30

Series: CTC Seminar
Date: Wednesday 30-Nov-2022
Time: 11:30-12:30 pm
Location: PSC 1136
Speaker: Aleksandra Hamanowicz
Title: "Two talks. 1. METAL-Z – measuring dust depletion in the low metallicity environments. 2: Dramatic Evolution in the Dusty ISM Across the Local Group"

Abstract 1: A critical yet poorly understood aspect of the baryon cycle in galaxies is the depletion of metals from the gas to the dust phase via dust formation, and vice versa, the return of heavy elements from the dust to the gas phase via dust destruction. Understanding dust depletion is especially crucial in the low metallicity regime (5-10 % solar), corresponding to the typical metallicity of Damped Lyman-alpha (DLA) systems, which are used to track the chemical enrichment of the universe. Corrections for dust depletion in abundance measurements in DLAs rely on locally-derived calibrations of depletions based on abundance ratios. Yet, these calibrations do not exist at metallicities lower than that of the SMC. In this talk, I will present results from the METAL-Z Hubble program (GO-15880), which obtained COS spectra toward UV-bright O/early B stars in local dwarf galaxies IC1613 (0.15 Z_sun) and Sextans-A (0.08 Z_sun), with the goal to measure dust depletions in these low metallicity environments. We combine the gas-phase abundances derived from METAL-Z with photospheric abundance measurements in young OBA stars from the literature to derive interstellar depletions of iron and sulfur, two key elements for understanding the chemical enrichment of the universe. Combined with depletion measurements available in the Milky Way, LMC (0.5 Z_sun), and SMC (0.2 Z_sun), the METAL-Z measurements allow us to constrain dust depletions as a function of metallicity down to 0.08 Z_sun. Abstract 2: I will present the evolution of the dust-to-gas ratio with density for four well-resolved galaxies in the local group - the LMC, SMC, M31, and M33. We explore this using new Herschel maps of these galaxies, which restore extended dust emission that had been missed by previous Herschel reductions. Combining this sensitivity to diffuse dust emission with excellent angular - and hence physical - resolution, allows us to probe the dust-to-gas ratio across 2.5 orders of magnitude in ISM surface density. We find very strong evolution in the dust-to-gas with density, by as much as a factor of 22 within a single galaxy. This is strong evidence for very high levels of dust grain growth in the denser regions of the ISM. We find M31 and M33 have very similar dust-to-gas evolution profiles, despite their large differences in mass, metallicity, and star formation rate; conversely, we find M33 and the LMC to have very different dust-to-gas evolution profiles, despite their close similarity in terms of mass, metallicity, and star formation rate. Our dust-to-gas ratios address previous disagreement between UV- and FIR-based dust-to-gas estimates for the Magellanic Clouds, removing the disagreement for the LMC, and considerably reducing it for the SMC - with our new dust-to-gas measurements being factors of >2 greater than the previous far-infrared estimates. This indicates how issues with angular sensitivity & data calibration can lead to dust-to-gas ratios being underestimated, especially at lower metallicities, with implications for the vast majority of low-metallicity galaxies for which available far-infrared data is poorly- or un-resolved.

Guidelines and format for the CTC Lunch seminars.
Past CTC Lunch seminars.
For other questions, contact the CTC Lunch host: Shmuel Bialy


Special accommodations for individuals with disabilities can be made by calling (301) 405-3001. It would be appreciated if we are notified at least one week in advance.


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