Bright Source Subtraction Requirements For Redshifted 21 cm Measurements

TL;DR

This paper examines the requirements for removing bright extragalactic sources to enable detection of the redshifted 21 cm signal, focusing on the accuracy needed in source positions and calibration for upcoming radio telescopes.

Contribution

It quantifies the precision needed in source position and calibration to effectively subtract foregrounds in 21 cm cosmology observations.

Findings

0.1 arcsec source position accuracy suffices for detection

0.05% antenna gain calibration accuracy needed

Residual contamination localized at small angular scales

Abstract

The \hi 21 cm transition line is expected to be an important probe into the cosmic dark ages and epoch of reionization. Foreground source removal is one of the principal challenges for the detection of this signal. This paper investigates the extragalactic point source contamination and how accurately bright sources ($\gtrsim 1$ ~Jy) must be removed in order to detect 21 cm emission with upcoming radio telescopes such as the Murchison Widefield Array (MWA). We consider the residual contamination in 21 cm maps and power spectra due to position errors in the sky-model for bright sources, as well as frequency independent calibration errors. We find that a source position accuracy of 0.1 arcsec will suffice for detection of the \hi power spectrum. For calibration errors, 0.05 % accuracy in antenna gain amplitude is required in order to detect the cosmic signal. Both sources of subtraction error produce residuals that are localized to small angular scales, $\kperp \gtrsim 0.05 $Mpc$^{-1}$, in the two-dimensional power spectrum.