NONCOSMOLOGICAL SIGNAL CONTRIBUTIONS TO THE COBE DMR-4 YEAR SKY MAPS

We limit the possible contributions from noncosmological sources to th e COBE Differential Microwave Radiometer (DMR) 4 year sky maps. The DM R data are cross-correlated with maps of rich clusters, extragalactic IRAS sources, HEAO I A-2 X-ray emission, and 5 GHz radio sources using a Fourier space technique. There is no evidence of significant contam ination by such sources at an rms level of similar to 8 mu K [95% conf idence level (c.l.) at 70 resolution] in the most sensitive 53 GHz sky map. This level is consistent with previous limits set by analysis of earlier DMR data and by simple extrapolations from existing source mo dels. We place a limit on the rms Comptonization parameter averaged ov er the high-latitude sky of delta gamma < 1 x 10(-6) (95% c.l.). Extra galactic sources have an insignificant effect on the cosmic microwave background power spectrum parameterizations determined from the DMR da ta.