High-Latitude Galactic Emission in the COBE DMR Two-Year Sky Maps

Abstract

We cross-correlate the COBE-DMR 2-year sky maps with spatial templates from long-wavelength radio surveys and the far-infrared COBE DIRBE maps. We place an upper limit on the spectral index of synchrotron radiation beta_{synch} < -2.9 between 408 MHz and 31.5 GHz. We obtain a statistically significant cross-correlation with the DIRBE maps whose dependence on the DMR frequencies indicates a superposition of dust and free-free emission. The high-latitude dust emission (|b| > 30 deg) is well fitted by a single dust component with temperature T = 18 (+3, -7) K and emissivity epsilon ~ nu^beta with beta = 1.9 (+3.0, -0.5). The free-free emission is spatially correlated with the dust on angular scales larger than the 7 degree DMR beam, with rms variations 5.3 +/- 1.8 uK at 53 GHz and angular power spectrum P ~ ell^{-3}. If this correlation persists to smaller angular scales, free-free emission should not be a significant contaminant to measurements of the cosmic microwave anisotropy at degree angular scales for frequencies above 20 GHz.