SEVEN-YEAR <i>WILKINSON MICROWAVE ANISOTROPY PROBE</i> ( <i>WMAP</i> ) OBSERVATIONS: GALACTIC FOREGROUND EMISSION

Abstract

We present updated estimates of Galactic foreground emission using seven years of WMAP data. Using the power&#13;\nspectrum of differences between multi-frequency template-cleaned maps, we find no evidence for foreground&#13;\ncontamination outside of the updated (KQ85y7) foreground mask.We place a 15μK upper bound on rms foreground&#13;\ncontamination in the cleaned maps used for cosmological analysis. Further, the cleaning process requires only three&#13;\npower-law foregrounds outside of the mask. We find no evidence for polarized foregrounds beyond those from soft&#13;\n(steep-spectrum) synchrotron and thermal dust emission; in particular we find no indication in the polarization data&#13;\nof an extra “haze” of hard synchrotron emission from energetic electrons near the Galactic center. We provide an&#13;\nupdated map of the cosmic microwave background (CMB) using the internal linear combination method, updated&#13;\nforeground masks, and updates to point source catalogs using two different techniques. With additional years of&#13;\ndata, we now detect 471 point sources using a five-band technique and 417 sources using a three-band CMB-free&#13;\ntechnique. In total there are 62 newly detected point sources, a 12% increase over the five-year release. Also new&#13;\nare tests of theMarkov chain Monte Carlo foreground fitting procedure against systematics in the time-stream data,&#13;\nand tests against the observed beam asymmetry. Within a few degrees of the Galactic plane, the behavior in total&#13;\nintensity of low-frequency foregrounds is complicated and not completely understood. WMAP data show a rapidly&#13;\nsteepening spectrum from 20 to 40 GHz, which may be due to emission from spinning dust grains, steepening&#13;\nsynchrotron, or other effects. Comparisons are made to a 1 deg 408 MHz map (Haslam et al.) and the 11 deg&#13;\nARCADE 2 data (Singal et al.).We find that spinning dust or steepening synchrotron models fit the combination of&#13;\nWMAP and 408 MHz data equally well. ARCADE data appear inconsistent with the steepening synchrotron model&#13;\nand consistent with the spinning dust model, though some discrepancies remain regarding the relative strength&#13;\nof spinning dust emission. More high-resolution data in the 10–40 GHz range would shed much light on these&#13;\nissues.