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2018 Hot Sci @ STScI

Probing Dust Properties in the Magellanic Clouds with the UV to FIR

Presented by: Julia Roman-Duval (Space Telescope Science Institute)
Category: Science Colloquia   Duration: 30 minutes   Broadcast date: July 18, 2018
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7/18/18 Julia Roman-Duval (STScI) Title: Probing Dust Properties in the Magellanic Clouds with the UV to FIR Abstract: Interstellar dust is a key component of galaxy evolution owing to its crucial role in the chemistry and radiative transfer in galaxies. Our interpretation of extragalactic SEDs and our understanding of galaxy evolution thus critically depend on an accurate characterization of how the dust content and properties vary within and between galaxies. Recent observations suggest that dust grains must grow in the ISM to explain dust masses over cosmic times, leading to changes in the abundance, composition, size, and optical properties of dust grains with environment (e.g., density, metallicity, dynamics). In this talk, I will present results from two recent efforts to characterize the dust properties in the Magellanic Clouds. First, an analysis of the gas-to-dust ratio variations in the LMC and SMC (with metallicitmetallicities 0.5 and 0.2 solar, respectively) based on the stacking and modeling of the resolved SED from all-sky FIR surveys shows that the dust abundance increases by factors 3-7 between the diffuse ISM and dense molecular clouds. Second, the large Hubble Space Telescope (HST) program METAL (Metal Evolution, Transport, and Abundance in the LMC) is delivering its first large sample of interstellar depletions at half-solar metallicity toward 33 massive stars in the LMC. The gas-phase abundances of the key components of dust grains (Si, Mg, Fe, Ni) but also other volatile elements (Zn, S) strongly support dust growth in the ISM via accretion of gas-phase metals onto dust grains. Depletion patterns however differ between the Milky Way, the LMC, and SMC, with the dust-to-metal ratio offsetting almost exactly the metallicity differences, leading to constant gas-phase metallicities in those galaxies. The depletion parameter measured in METAL correlates linearly with the absolute-to-selective extinction ratio, R_V, in a subset of seven METAL sight-lines for which extinction curves are already published, potentially indicating a direct link between the level of depletion in the gas and the size of dust grains. Additionally, parallel WFC3 imaging obtained as part of METAL allows us to derive high-resolution extinction maps, which can be directly compared to FIR emission seen in Spitzer and Herschel to characterize the FIR dust emissivity. The METAL program will comprehensively improve our understanding of dust properties, the sub-grid modeling of galaxy evolution, and the accuracy with which dust-based gas masses, star formation rates and histories in nearby and high-redshift galaxies are estimated.