Study of systematics effects on the Cross Power Spectrum of 21 cm Line and Cosmic Microwave Background using Murchison Widefield Array Data

TL;DR

This study investigates the cross power spectrum between 21cm line observations and the CMB using MWA data, addressing systematics and foreground removal to improve detection prospects during the Epoch of Reionization.

Contribution

It presents the first measurement of the 21cm-CMB cross power spectrum with MWA data and demonstrates foreground removal techniques to reduce errors and address systematics.

Findings

CPS is consistent with zero within current errors.

Foreground removal reduces error by an order of magnitude.

Detection requires extensive observation and foreground suppression.

Abstract

Observation of the 21cm line signal from neutral hydrogen during the Epoch of Reionization is challenging due to extremely bright Galactic and extragalactic foregrounds and complicated instrumental calibration. A reasonable approach for mitigating these problems is the cross correlation with other observables. In this work, we present the first results of the cross power spectrum (CPS) between radio images observed by the Murchison Widefield Array and the cosmic microwave background (CMB), measured by the Planck experiment. We study the systematics due to the ionospheric activity, the dependence of CPS on group of pointings, and frequency. The resulting CPS is consistent with zero because the error is dominated by the foregrounds in the 21cm observation. Additionally, the variance of the signal indicates the presence of unexpected systematics error at small scales. Furthermore, we reduce the error by one order of magnitude with application of a foreground removal using a polynomial fitting method. Based on the results, we find that the detection of the 21cm-CMB CPS with the MWA Phase I requires more than 99.95% of the foreground signal removed, 2000 hours of deep observation and 50% of the sky fraction coverage.