Point Sources in the Cosmic Microwave Background

Non-Gaussian imprints on the cosmic microwave background radiation (CBR) sky are within the grasp of current experiments. A clear non-Gaussian signature would be point-like sources. We have examined the nature of possible point sources that were tentatively identified in a recent high frequency CBR experiment with half-degree resolution (Cheng et al. 1994: MSAM). The effects of local foreground sources, including cold dust clouds, radio sources and the Sunyaev-Zeldovich effect due to foreground rich clusters are considered, and the effective spectral slopes of these various foreground contaminations are calculated. Radio source emission and the Sunyaev-Zeldovich effect are ruled out as the explanation of the possible MSAM sources. Modeles are examined of extremely cold dust clouds which are located in the solar neighborhood, the interstellar medium, the galactic halo or at cosmological distances. We estimate the cloud mass and dust grain parameters, and in particular the grain size distribution, that are required in order to produce a detectable signal in an MSAM-type experiment. It is shown that cold dust clouds can have an important effect on CBR experiments only if the clouds are nearby, and located within a disc scale height of the solar neighborhood. Cold dust emission remains a possible source of far-infrared signal at the level of the detected CBR fluctuations on degree scales, but may be ruled out if the dust emissivity index satisfies $\alpha = 1.5 \pm 0.5$ .