A Method to Extract the Angular Power Spectrum of the Epoch of Reionization from Low-Frequency Radio Interferometers

TL;DR

This paper introduces a new method to extract the angular power spectrum of the Epoch of Reionization from low-frequency radio interferometer data by using visibility correlation coefficients, reducing calibration dependencies.

Contribution

The novel approach uses correlation coefficients instead of raw visibilities to determine the EoR power spectrum, minimizing calibration errors and simplifying analysis.

Findings

Method successfully extracts the angular power spectrum from simulated data.

Reduces influence of receiver gain variations on measurements.

Demonstrated feasibility with 21CMA interferometer simulations.

Abstract

The redshifted 21cm signal of neutral hydrogen from the epoch of reionization (EoR) is extremely weak and its first detection is therefore expected to be statistical with first-generation low-frequency radio interferometers. In this letter we propose a method to extract the angular power spectrum of EoR from the visibility correlation coefficients p_{ij}(u,v), instead of the visibilities V_{ij}(u,v) measured directly by radio interferometers in conventional algorithm. The visibility correlation coefficients are defined as p_{ij}(u,v)=V_{ij}(u,v)/\sqrt{|V_{ii}||V_{jj}|} by introducing the auto-correlation terms V_{ii} and V_{jj} such that the angular power spectrum C_{\ell} can be obtained through C_{\ell}=4pi^2T_0^2<|p_{ij}(u,v)|^2>, independently of the primary beams of antennas. This also removes partially the influence of receiver gains in the measurement of C_{\ell} because the amplitudes of the gains cancel each other out in the statistical average operation of <|p_{ij}(u,v)|^2>.We use the average system temperature T_0 as a calibrator of C_{\ell}, which is dominated by the Milky Way and extragalactic sources in our interested frequency range below 200 MHz. Finally we demonstrate the feasibility of the novel method using the simulated sky maps as targets and the 21 CentiMeter Array (21CMA) as interferometer.