It's true, folks: The dust that radiates in the infrared is the same as the dust that absorbs in the visible and ultraviolet! Some may say this has been known for decades, but I successfully confirmed it today by comparing the dust models I can make for multi-band Herschel data on the M31 disk with extinction maps made from HST-imaging visible and UV stellar colors by Karl Gordon and Julianne Dalcanton of the PHAT Collaboration. My comparison is purely qualitative at present but I hope in the next week or two to make it quantitative. I want to find the combination of emission-inferred dust column, temperature, and emissivity parameter that best predicts the visible extinction; I then hope to find that it is only the column that is heavily involved in the prediction. That would be a great success of my (completely trivial, null) dust absorber and emitter model. I discussed all this today in one of the MPIA lounges with Ben Weiner (Arizona), Brent Groves (MPIA), Karin Sandstrom (MPIA), and Rix, with cameos by Thomas Henning (MPIA) and Tom Herbst (MPIA).
Oh, and not surprising. I've been thinking/working on this very subject and should mention that both optical A(V) and far-IR dust column are measuring similar, but not the same thing. The A(V) probably needs an R(V) dependent correction and the far-IR needs some kind of correction for dust coagulation (also probed by R(V)). I would say that the two measures should be the same within a factor of 2 w/o these corrections.
ReplyDeleteNeat work! I'm not sure if it would provide any information for your dust model above and beyond the stellar colors, but we do have optical spectra of ~600 emission line regions in M31 that provide precise radial velocities and a reddening estimate from the Balmer decrement.
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