Observational Constraints on Microwave Anisotropy from Point Sources

Applying basic physical principles to recent observational results, we derive upper and lower limits on microwave anisotropy from point sources over the range of frequencies 10-1000 GHz. We examine the level of noise in the observations as a possible indication of source confusion at subarcminute scales. We also derive an upper limit on microwave anisotropy caused by the sources responsible for the Far-Infrared Background radiation detected in FIRAS data. Our upper limit on point source confusion of DeltaT/T=10^{-5} for a 10' beam at 100 GHz would cause severe foreground contamination for CMB anisotropy observations, although the actual contamination level is probably much lower. This upper limit constrains the long-feared possibility of an undetected population of sources with emission peaking near 100 GHz. Source detections closer to 100 GHz are needed to improve our knowledge of galaxy evolution at high redshift and to predict the level of point source confusion