B-Mode contamination by synchrotron emission from 3-years WMAP data

TL;DR

This study assesses Galactic synchrotron contamination in the lowest emission sky regions using WMAP data, showing these areas could enable detection of primordial B-mode signals at low tensor-to-scalar ratios, aiding inflationary research.

Contribution

It provides the first comprehensive analysis of synchrotron contamination in the lowest emission regions, demonstrating their potential for primordial B-mode detection.

Findings

Synchrotron emission can mimic B-mode signals for T/S ratios of 10^{-3} to 10^{-2} at 70 GHz.

Lowest emission regions have less contamination than previously estimated for high Galactic latitudes.

These regions could allow direct measurement of T/S ~ 10^{-3}, aiding inflationary studies.

Abstract

We study the contamination of the B-mode of the Cosmic Microwave Background Polarization (CMBP) by Galactic synchrotron in the lowest emission regions of the sky. The 22.8-GHz polarization map of the 3-years WMAP data release is used to identify and analyse such regions. Two areas are selected with signal-to-noise ratio S/N<2 and S/N<3, covering ~16% and ~26% fraction of the sky, respectively. The polarization power spectra of these two areas are dominated by the sky signal on large angular scales (multipoles l < 15), while the noise prevails on degree scales. Angular extrapolations show that the synchrotron emission competes with the CMBP B-mode signal for tensor-to-scalar perturbation power ratio $T/S = 10^{-3}$ -- $10^{-2}$ at 70-GHz in the 16% lowest emission sky (S/N<2 area). These values worsen by a factor ~5 in the S/N<3 region. The novelty is that our estimates regard the whole lowest emission regions and outline a contamination better than that of the whole high Galactic latitude sky found by the WMAP team (T/S>0.3). Such regions allow $T/S \sim 10^{-3}$ to be measured directly which approximately corresponds to the limit imposed by using a sky coverage of 15%. This opens interesting perspectives to investigate the inflationary model space in lowest emission regions.