Significant foreground unrelated non-acoustic anisotropy on the one degree scale in WMAP 5-year observations

Abstract

The spectral variation of the cosmic microwave background (CMB) as observed by WMAP was tested using foreground reduced WMAP5 data, by producing subtraction maps at the 1$^\circ$ angular resolution between the two cosmological bands of V and W, for masked sky areas that avoid the Galactic disk. The resulting $V-W$ map revealed a non-acoustic signal over and above the WMAP5 pixel noise, with two main properties. Firstly, it possesses quadrupole power at the $\approx$ 1 $\mu K$ level which may be attributed to foreground residuals. Second, it fluctuates also at all values of $\ell >$ 2, especially on the $1^\circ$ scale ($200 \lesssim \ell \lesssim 300$). The behavior is {\it random and symmetrical} about zero temperature with a r.m.s. amplitude of $\approx$ 7 $\mu K$, or 10 % of the maximum CMB anisotropy, which would require a `cosmic conspiracy' among the foreground components if it is a consequence of their existences. Both anomalies must be properly diagnosed and corrected if `precision cosmology' is the claim. The second anomaly is, however, more interesting because it opens the question on whether the CMB anisotropy genuinely represents primordial density seeds.