(Appears in Astrophysical Journal Letters, 1996 Feb 10 issue - vol. 458, L1)
The Contribution of Galactic Free-Free Emission
to Anisotropies in the Cosmic Microwave Background
Found by the Saskatoon Experiment
John H. Simonetti, Brian Dennison, and Gregory A. Topasna
Martin Observatory, Institute for Particle Physics and Astrophysics,
and Department of Physics,
Virginia Polytechnic Institute and State University,
Blacksburg, VA 24061
We made a sensitive, wide-field H-alpha 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 (Wollack et al. 1993, Netterfield et al. 1995). The analysis
of the H-alpha 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 85degree declination circle. We found no such
irregularities that could be attributed to H-alpha emission. The implied
upper-bound on the rms variation in free-free brightness temperature is
4.6 microK at 27.5GHz. 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.