University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Monday, February 22nd 2016
12:15 pm:
Speaker: Christopher Sheehy, KICP Fellow, University of Chicago
Subject: Measuring CMB Spectral Distortions from the Ground

COBE/FIRAS famously measured the CMB's absolute intensity spectrum to be that of a nearly perfect blackbody. There are, however, a number of physical processes in the universe that guarantee measurable deviations. Recent renewed interest in CMB spectrum measurements has mainly focused on two classes of spectral distortions, the so-called mu- and y-distortions, which can only be measured from space and are the targets of a proposed NASA satellite mission. In this talk, I will focus on a third class of spectral distortions, the recombination spectral lines, which are relatively narrow features in the CMB spectrum originating from electronic transitions of hydrogen and helium at the time of recombination. In particular, I will discuss the possibility of measuring the recombination lines from the ground without the need for absolute intensity calibration. I will highlight a small pathfinder experiment currently under construction that will determine the suitability of one proposed technique to do this, an array of elevation tipping radiometers operating at 2-4 GHz. If a measurement is possible, the influence of helium on the line positions would allow for a direct and clean measurement of Y_p.

Faculty Host: Clement Pryke

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