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We made a sensitive, wide-field H image of the north celestial polar region. Using this image, we constrain the contribution of irregularities in interstellar free-free emission to the degree-scale anisotropies in the cosmic microwave background detected in recent observations at Saskatoon by the Princeton group. The analysis of the H image mimics the Saskatoon data analysis: the resulting signal is the strength of irregularities sampled with the Saskatoon beam (i.e., degree-scale) along the 85 declination circle. We found no such irregularities that could be attributed to H emission. The implied upper bound on the rms variation in free-free brightness temperature is less than 4.6 K at 27.5 GHz. The observed cosmic microwave background anisotropies are much larger. Therefore, the contribution of irregularities in interstellar free-free emission to the observed anisotropies is negligible.
Simonetti et al. (Sat,) studied this question.