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arXiv · 2302.07378

The Quest for the Missing Dust: II -- Two Orders of Magnitude of Evolution in the Dust-to-Gas Ratio Resolved Within Local Group Galaxies

Christopher J. R. Clark·Julia C. Roman-Duval·Karl D. Gordon·Caroline Bot·Matthew W. L. Smith·Lea M. Z. Hagen
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Abstract

We explore evolution in the dust-to-gas ratio with density within four well-resolved Local Group galaxies - the LMC, SMC, M31, and M33. We do this using new ${\it Herschel}$ maps, which restore extended emission that was missed by previous ${\it Herschel}$ reductions. This improved data allows us to probe the dust-to-gas ratio across 2.5 orders of magnitude in ISM surface density. We find significant evolution in the dust-to-gas ratio, with dust-to-gas varying with density within each galaxy by up to a factor 22.4. We explore several possible reasons for this, and our favored explanation is dust grain growth in denser regions of ISM. We find that the evolution of the dust-to-gas ratio with ISM surface density is very similar between M31 and M33, 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 those properties. 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. We also observe that the dust-to-gas ratio appears to fall at the highest densities for the LMC, M31, and M33; this is unlikely to be an actual physical phenomenon, and we posit that it may be due to a combined effect of dark gas, and changing dust mass opacity.

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Christopher J. R. Clark, Julia C. Roman-Duval, Karl D. Gordon, Caroline Bot, Matthew W. L. Smith, Lea M. Z. Hagen. 2023-02-14. The Quest for the Missing Dust: II -- Two Orders of Magnitude of Evolution in the Dust-to-Gas Ratio Resolved Within Local Group Galaxies. https://doi.org/10.3847/1538-4357/acbb66

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