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

We have observed the region of the sky north of 81° declination with a wide-angle CCD camera and narrow-band (1 nm) Hα filter. After subtracting the stellar background using off-band images and smoothing to 0.̊1 resolution, we set an upper limit on the anisotropy in the Hα 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 μK. Thus no more than 7% of the 44 μK anisotropy observed by Netterfield et al. (ApJ, 331, 341, 1995) can be due to free-free emission by Galactic hydrogen.