High-Latitude Galactic Emission in the COBE Differential Microwave Radiometer 2 Year Sky Maps

We cross-correlate the COBE⁶ 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 βsynch < -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°) is well fitted by a single dust component with temperature T = 18⁺³₋₇ K and emissivity ν ∝ (υ/ν₀)β with β = 1.9+3.0-0.5. The free-free emission is spatially correlated with the dust on angular scales larger than the 70 DMR beam, with rms variations 5.3±1.8 μK at 53 GHz and angular power spectrum p ∝ l⁻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.