Cross-correlation between the 170 GHz survey map and the COBE differential microwave radiometer first-year maps

This Letter describes results of a cross-correlation between the 170 GHz partial-sky survey, made with a 3°.8 beam balloon-borne instrument, and the COBE DMR "Fit Technique" reduced galaxy all-sky map with a beam of 7°. The strong correlation between the data sets implies that the observed structure is consistent with thermal variations in a 2.7 K emitter. We describe a number of tests of the correlation: (1) A χ² analysis applied to the correlation function rules out the assumption that there is no structure in either of the two maps. (2) A second test shows that if the DMR map has structure but the 170 GHz map does not, the probability of obtaining the observed correlation is small. (3) Further analyses support the assumption that both maps have structure and that the 170 GHz-DMR cross-correlation is consistent with the analogous DMR correlation function. (4) Maps containing various combinations of noise and Harrison-Zel'dovich power spectra are simulated and correlated to reinforce the result. Because these two experiments use completely different observing strategies, observing frequencies, and data reduction methods, the correlation provides compelling evidence that both instruments have observed fluctuations consistent with anisotropies in the cosmic microwave background.