University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Friday, May 1st 2015
Speaker: John Vaillancourt, SOFIA
Subject: The Polarized, Dusty Interstellar Medium

Polarized radiation at optical through millimeter wavelengths arises from thermally emitting dust grains whose axes exhibit a net alignment with the local magnetic field. As a result of this mechanism, polarization observations have successfully provided one of the few methods for measuring astrophysical magnetic field strengths and structure in a wide range of objects, from young protostars to external galaxies. The physical mechanisms proposed for aligning the grains have met some, but not every, observational test (i.e., correlations between polarization and reddening, spectral dependence, and grain composition). In the absence of a well-understood alignment model, the aforementioned magnetic field measurements would all be suspect.

Here I will introduce some key predictions from grain alignment models and discuss the observational successes and failures of each, leading to a preferred model in which interstellar radiation drives grain alignment. Additional tests of this radiative alignment torque model should be possible with new facilities such as ALMA, HAWC/SOFIA, and recently released Planck polarization data.

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