An Upper Limit on the Contribution of Galactic Free-Free Emission to the Cosmic Microwave Background near the North Celestial Pole

摘要

We have observed the region of the sky north of 81 degrees declination with a wide-angle CCD camera and narrow-band (1 nm) H-alpha filter. After subtracting the stellar background using offband images and smoothing to 0.1 degree resolution, we set an upper limit on the anistropy in the H-alpha emission at this angular scale of 1.3 Rayleigh. At degree angular scales, the upper limit is 0.5 R, which corresponds to an anisotropy in the brightness temperature of the free-free emission at 32 GHz of 3 muK. Thus no more than 7% of the 44 muK anistropy observed by Netterfield et al. (1995) can be due to free-free emission by Galactic hydrogen.