18 February 2020Dust evolution in Milky Way PDRs and Andromeda

Dust plays a fundamental role in the evolution of interstellar medium and of galaxies. Astrophysical observations combined to numerical models and laboratory studies of dust analogues improve our comprehension of the nature and the physics of interstellar grains. However the processes responsible for dust evolution are still poorly constrained.

Thanks to Herschel Space Observatory, we have been able to observe dust emission on short spatial scales in several photodissociation regions (PDRs). Such regions are ideal laboratories to infer dust evolution since they are at the interface between ionized and molecular regions. I will highlight the varying properties of dust across PDRs by comparing a radiative transfer dust model to these observations. 

Besides direct observations, resolved star surveys contain wealthy information on dust too. To extract them, we have developed the Bayesian Extinction And Stellar Tool (BEAST). Given a set of photometric measurements and an observational uncertainty model, the BEAST infers the physical properties of the stellar source and constrains the line of sight extinction. I will present the capacities and results of this new tool applied to the Panchromatic Hubble Andromeda Treasury (PHAT) survey which gathers around 100 million stars and covers a third of M31. Finally, by comparing the M31 extinction parameter maps to Herschel derived dust mass maps, I will show evidence of dust emissivity variation revealing grain evolution on large scales in M31.