Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations:
  Galactic Foreground Emission
  [Abridged] We present updated estimates of Galactic foreground emission using
seven years of WMAP data. Using the power spectrum of differences between
multi-frequency template-cleaned maps, we find no evidence for foreground
contamination outside of the updated (KQ85y7) foreground mask. We place a 15
microKelvin upper bound on rms foreground contamination in the cleaned maps
used for cosmological analysis. We find no indication in the polarization data
of an extra "haze" of hard synchrotron emission from energetic electrons near
the Galactic center. We provide an updated map of the cosmic microwave
background (CMB) using the internal linear combination (ILC) method, updated
foreground masks, and updates to point source catalogs with 62 newly detected
sources. Also new are tests of the Markov chain Monte Carlo (MCMC) foreground
fitting procedure against systematics in the time-stream data, and tests
against the observed beam asymmetry.
  Within a few degrees of the Galactic plane, WMAP total intensity data show a
rapidly steepening spectrum from 20-40 GHz, which may be due to emission from
spinning dust grains, steepening synchrotron, or other effects. Comparisons are
made to a 1-degree 408 MHz map (Haslam et al.) and the 11-degree ARCADE 2 data
(Singal et al.). We find that spinning dust or steepening synchrotron models
fit the combination of WMAP and 408 MHz data equally well. ARCADE data appear
inconsistent with the steepening synchrotron model, and consistent with the
spinning dust model, though some discrepancies remain regarding the relative
strength of spinning dust emission. More high-resolution data in the 10-40 GHz
range would shed much light on these issues.
