Cross Terms and Weak Frequency Dependent Signals in the CMB Sky

Details Cross Terms and Weak Frequency Dependent Signals in the CMB Sky Cross Terms and Weak Frequency Dependent Signals in the CMB Sky

2004-05-25

arxiv.org/abs/astro-ph/0405487v2

Mon.Not.Roy.Astron.Soc.359:597-614,2005

Astronomy and Astrophysics

Astrophysics

11 pages, 5 figures, minor comments regarding impact of noise added, matches accepted version in MNRAS

Scientific paper

10.1111/j.1365-2966.2005.08929.x

In this paper, we study the amplification of weak frequency dependent signals in the CMB sky due to their cross correlation to intrinsic anisotropies. In particular, we center our attention on mechanisms generating some weak signal, of peculiar spectral behaviour, such as resonant scattering in ionic, atomic or molecular lines, thermal SZ effect or extragalactic foreground emissions, whose typical amplitude (denoted by $\epsilon$) is sufficiently smaller than the intrinsic CMB fluctuations. We find that all these effects involve either the autocorrelation of anisotropies generated during recombination ($z_{rec}$) or the cross-correlation of those anisotropies with fluctuations arising at some later redshift $z_i$. The degree of this correlation can be computed under the assumption that density fluctuations were generated as standard inflationary models dictate and that they evolved in time according to linear theory. In case that the weak signal is frequency dependent, we show that, by substracting power spectra at different frequencies, it is possible to avoid the limit associated to Cosmic Variance and unveil weaker terms linear in $\epsilon$. We find that the correlation term shows a different spectral dependence than the squared ($\propto \epsilon^2$) term considered usually, making its extraction particularly straightforward for the thermal SZ effect. Furthermore, we find that in most cases the correlation terms are particularly relevant at low multipoles and must be taken into account when characterising the power spectrum associated to weak signals in the large angular scales.

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