The Optical-Infrared Extinction Curve and its Variation in the Milky Way

The dust extinction curve is a critical component of many observational programs and an important diagnostic of the physics of the interstellar medium.  In this talk, I will present new measurements of the dust extinction curve and its variation towards tens of thousands of stars, a hundred-fold larger sample than in existing detailed studies.  We use data from the APOGEE spectroscopic survey in combination with ten-band photometry from Pan-STARRS1, 2MASS, and WISE.  Our data and analysis have revealed two new aspects of Galactic extinction: first, we find significant, wide-area variations in the shape of the extinction curve throughout the Galactic plane.  These variations are on scales much larger than individual molecular clouds, posing a challenge to existing paradigms of dust formation and processing: the extinction curve must be tracing much more than just grain growth in dense molecular regions.  Indeed, we find no correlation between the extinction curve shape and and dust column density up to E(B-V) ~ 2.  Second, we discover a strong relationship between shape of the extinction curve and the far-infrared dust emissivity, an important new constraint on models of dust physics.

Speaker: Eddie Schlafly, UC Berkeley