Mapping the Galactic Free-Free Foreground via Interstellar H-Alpha Emission

Abstract

Recently completed H-Alpha surveys of large portions of the sky can be used to create maps of the free-free intensity distribution at high Galactic latitude that are independent of the spectral fits to the CMB data. This provides an opportunity to test the accuracy of the spectral fitting procedures and to search for other sources of Galactic forground contamination that could be confused spectrally with the free-free, such as spinning dust grains. The Wisconsin H-Alpha Mapper (WHAM) survey has sampled the sky north of declination -30 deg at about one degree angular resolution and has revealed that, except for a few isolated regions of enhanced emission, ΔT_{ff} (30 GHz) < 30 micro-K at Galactic latitudes near 15 deg, decreasing to ΔT_{ff} (30 GHz) < 4 mircro-K at latitudes above 50 deg. Also in progress are H-Alpha surveys that sample the sky at higher angular resolution.