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Wednesday 15 Jun 2022Evolution in the Dusty ISM Across the Local Group

Christopher Clark - Space Telescope Science Institute

4th Floor Physics + remote 16:00-17:00

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 those same parameters. 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 2.4 and 2.0 greater than the previous far-infrared estimates, respectively. This indicates how important it is to use data that is sensitive to emission on all spatial scales, when examining well-resolved ISM. We also find evidence for significant amounts of dark gas, and density-dependence of the dust mass absorption coefficient.

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