The spectrum of the cosmic microwave background anisotropy from the combined COBE FIRAS and DMR observations

We analyze the cosmic microwave background (CMB) anisotropy data from the independent COBE FIRAS and DMR observations. We extract the frequency spectrum of the FIRAS signal that has the spatial distribution seen by DMR and show that it is consistent with CMB temperature fluctuations in the radiation well into the Wien region of the spectrum. Conversely, we form a map of the Planckian component of the sky temperature from FIRAS and show that it correlates with the DMR anisotropy map. The rms fluctuations at angular scales of 7 degrees are 48 +/- 14 mu K for the FIRAS data versus 35 +/- 2 mu K for the DMR data and 31 +/- 6 mu K for the combination (1 sigma uncertainties). The consistency of these data, from very different instruments with very different observing strategies, provides compelling support for the interpretation that the signal seen by DMR is, in fact, temperature anisotropy of cosmological origin. The data also limit rms fluctuations in the Compton y parameter, observable via the Sunyaev-Zeldovich effect, to Delta y < 3 x 10(-6) (95% CL) on 7 degrees angular scales.