Efficient ILC analysis on polarization maps after EB leakage correction

TL;DR

This paper extends the ILC method for CMB polarization analysis on small sky patches, combining it with template cleaning to eliminate EB leakage effects, thereby improving component separation efficiency in ground-based experiments.

Contribution

It introduces a novel ILC approach on pseudo-scalar B maps combined with template cleaning to remove EB leakage, enhancing polarization component separation accuracy.

Findings

Foreground residuals are well controlled in mock data.

Bias in tensor-to-scalar ratio r is about 10^{-3}.

Method improves efficiency of polarization analysis.

Abstract

The Internal Linear Combination (ILC) is widely used to extract the cosmic microwave background (CMB) signal from multi-frequency observation maps, especially for Satellite experiments with quasi-full sky coverage. We extend ILC method to CMB polarization map analysis with a small sky patch which is especially typical for ground-based experiments, by combing ILC with a template cleaning method which can give pure $B$ map free from $EB$ leakage caused by partial sky coverage. The feature of our methods is that we do the ILC analysis on pseudo-scalar $B$ maps, and the advantage is that it totally avoids the impact of $EB$ leakage on ILC, so that it can improve the efficiency of component separation dramatically. We demonstrate our methods with mock data of a future ground-based experiment with a deep survey on a clean patch in the northern sky, and the results show that the level of foreground residual can be well controlled, it biases the tensor to scalar ratio ($r$) at the order of $10^{-3}$ which is comparable to the statistical error by noise.