STRUCTURE IN THE COBE DIFFERENTIAL MICROWAVE RADIOMETER 1ST-YEAR MAPS

The first year of data from the Differential Microwave Radiometers (DMR) on the Cosmic Backgoround Explorer (COBE) show statistically significant (> 7-sigma) structure that is well described as scale-invariant fluctuations with a Gaussian distribution. The major portion of the observed structure cannot be attributed to known systematic errors in the instrument, artifacts generated in the data processing, or known Galactic emission. The structure is consistent with a thermal spectrum at 31, 53, and 90 GHz as expected for cosmic microwave background anisotropy. The rms sky variation, smoothed to a total 10-degrees FWHM Gaussian, is 30 +/- 5-mu-K (DELTA-T/T = 11 x 10(-6)) for Galactic latitude \b\ > 20-degrees data with the dipole anisotropy removed. The rms cosmic quadrupole amplitude is 13 +/- 4-mu-K (DELTA-T/T almost-equal-to 5 x 10(-6)). The angular autocorrelation of the signal in each radiometer channel and cross-correlation between channels are consistent and give a primordial fluctuation power-law spectrum with index n = 1.1 +/- 0.5, and an rms-quadrupole-normalized amplitude of 16 +/- 4-mu-K (DELTA-T/T almost-equal-to 6 x 10(-6)) . These features are in accord with the Harrison-Zel'dovich (scale-invariant, n = 1) spectrum predicted by models of inflationary cosmology. The low overall fluctuation amplitude is consistent with theoretical predictions of the minimal level gravitational potential variations that would give rise to the observed present day structure.