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

Recently completed Hα 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 Hα Mapper (WHAM) survey has sampled the sky north of declination −30 • at about one degree angular resolution and has revealed that, except for a few isolated regions of enhanced emission, ∆T f f (30 GHz) ∼ < 30 µK at Galactic latitudes near 15 • , decreasing to ∆T f f (30 GHz) ∼ < 4 µK at latitudes above 50 •. Also in progress are Hα surveys that sample the sky at higher angular resolution.