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

TL;DR

The study identifies unexpected anisotropy signals in WMAP 5-year data that challenge assumptions about foreground removal and raise questions about the primordial nature of CMB anisotropies.

Contribution

It reveals significant foreground-related anisotropy on the one-degree scale in WMAP data, questioning the purity of the primordial CMB signal.

Findings

Detected quadrupole power at ~1 μK level likely due to foreground residuals.

Observed fluctuations at all ℓ > 2, especially on 1° scale, with random symmetry.

Anomalies suggest potential contamination or new physics affecting CMB 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.