Colloquium: John Dickey (University of Tasmania) "GMIMS: Steps to the Polarization Horizon"

Date & time

11am–12pm 7 February 2018


Duffield Lecture Theatre (host: McIntyre)


John Dickey (University of Tasmania)



The polarized synchrotron emission of the Milky Way cosmic ray electrons propagates to us through a magneto-ionic medium that causes Faraday rotation. The emission process has been understood since the 1950s, but the astrophysics of the propagation of the polarized radiation has only recently become clear. With our gradual awakening to the concept of the Faraday spectrum over the last decade, we could design sky surveys that for the first time are sensitive to the full range of rotation measure of the polarized emission. The Global Magneto-Ionic Medium Survey (GMIMS) is a combination of such polarization surveys using different telescopes at different wavelengths. Now the results of two GMIMS surveys are available, from Parkes and the Dominion Radio Astrophysical Observatory (DRAO). In this talk I will explain the Faraday spectrum, show images of the sky that are sensitive to the full range of rotation measures for the first time, and then show how we can determine the distance to the emission regions. The polarization horizon is an analog to optical depth in an ordinary spectrum, that sets the limit for how far we can see.

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