Constraining Polarized Foregrounds for EOR Experiments II: Polarization Leakage Simulations in the Avoidance Scheme

TL;DR

This paper develops a formalism to simulate and understand polarization leakage from foregrounds in 21-cm EOR experiments, aiding in foreground subtraction to detect the cosmological signal.

Contribution

It extends the delay-spectrum approach to include polarized foreground leakage modeling, providing a tool for predicting and mitigating contamination in 21-cm observations.

Findings

Polarized point sources cause higher leakage than diffuse Galactic polarization at all k modes.

A foreground-free window exists at k > 0.3 h Mpc^{-1} despite polarization leakage.

The method can predict leakage from polarized foreground models, aiding in subtraction strategies.

Abstract

A critical challenge in the observation of the redshifted 21-cm line is its separation from bright Galactic and extragalactic foregrounds. In particular, the instrumental leakage of polarized foregrounds, which undergo significant Faraday rotation as they propagate through the interstellar medium, may harmfully contaminate the 21-cm power spectrum. We develop a formalism to describe the leakage due to instrumental widefield effects in visibility-based power spectra measured with redundant arrays, extending the delay-spectrum approach presented in Parsons et al. (2012). We construct polarized sky models and propagate them through the instrument model to simulate realistic full-sky observations with the Precision Array to Probe the Epoch of Reionization. We find that the leakage due to a population of polarized point sources is expected to be higher than diffuse Galactic polarization at any $k$ mode for a 30~m reference baseline. For the same reference baseline, a foreground-free window at $k > 0.3 \, h$~Mpc$^{-1}$ can be defined in terms of leakage from diffuse Galactic polarization even under the most pessimistic assumptions. If measurements of polarized foreground power spectra or a model of polarized foregrounds are given, our method is able to predict the polarization leakage in actual 21-cm observations, potentially enabling its statistical subtraction from the measured 21-cm power spectrum.