Comparing and combining the Saskatoon, QMAP, and COBE CMB maps - art. no. 103002

We present a method for comparing and combining maps with different resolut ions and beam shapes, and apply it to the Saskatoon, QMAP, and COBE-DMR dat a sets. Although the Saskatoon and QMAP maps detect signals at the 21 sigma and 40 sigma levels, respectively, their difference is consistent with pur e noise, placing strong limits on possible systematic errors. In particular , we obtain quantitative upper limits on relative calibration and pointing errors. Splitting the combined data by frequency shows similar consistency between the ka and Q bands, placing limits on foreground contamination. The visual agreement between the maps is equally striking. Our combined QMAP+S askatoon map, nicknamed QMASK, is publicly available on the web together wi th its 6495 x 6495 noise covariance matrix. This thoroughly tested data set covers a large enough area (648 square degrees-currently the largest degre e-scale map available) to allow a statistical comparison with COBE-DMR, sho wing good agreement.