Characterization of Extragalactic Point-Sources on E- and B-mode Maps of the CMB Polarization

TL;DR

This paper introduces a steerable wavelet filter operating on E- and B-mode polarization maps to characterize extragalactic point sources in CMB data, enhancing detection in low-intensity regions for future experiments.

Contribution

A novel steerable wavelet filter applied to E- and B-mode maps for improved extragalactic source characterization in CMB polarization data.

Findings

Effective in simulations of PICO satellite data.

Can detect sources down to 125 pK at 30 GHz.

Can characterize sources down to 14 pK at 155 GHz.

Abstract

Although interesting in themselves, extragalactic sources emitting in the microwave range (mainly radio-loud active galactic nuclei and dusty galaxies) are also considered a contaminant from the point of view of Cosmic Microwave Background (CMB) experiments. These sources appear as unresolved point-like objects in CMB measurements because of the limited resolution of CMB experiments. Amongst other issues, point-like sources are known to obstruct the reconstruction of the lensing potential, and can hinder the detection of the Primordial Gravitational Wave Background for low values of $r$. Therefore, extragalactic point-source detection and subtraction is a fundamental part of the component separation process necessary to achieve some of the science goals set for the next generation of CMB experiments. As a previous step to their removal, in this work we present a new filter based on steerable wavelets that allows the characterization of the emission of these extragalactic sources. Instead of the usual approach of working in polarization maps of the Stokes' $Q$ and $U$ parameters, the proposed filter operates on E- and B-mode polarization maps. In this way, it benefits from the lower intensity that, both, the CMB, and the galactic foreground emission, present in B-modes to improve its performance. To demonstrate its potential, we have applied the filter to simulations of the future PICO satellite, and we predict that, for the regions of fainter galactic foreground emission in the 30 GHz and 155 GHz bands of PICO, our filter will be able to characterize sources down to a minimum polarization intensity of, respectively, 125 pK and 14 pK. Adopting a $\Pi=0.02$ polarization degree, these values correspond to 169 mJy and 288 mJy intensities.