Parametrising Epoch of Reionization foregrounds: A deep survey of low-frequency point-source spectra with the MWA

TL;DR

This study measures high-resolution spectra of bright unresolved sources in the Epoch of Reionization field using MWA data, revealing instrumental effects and source spectral properties relevant for EoR signal detection.

Contribution

It introduces a novel peeling scheme for source subtraction and provides a detailed spectral catalogue, advancing understanding of foreground spectral behavior in EoR experiments.

Findings

Spectra are affected by instrumental effects limiting intrinsic source spectral constraints.

Residual spectra are dominated by PSF sidelobes from nearby sources.

Deep, confusion-limited MWA image achieved with 45 hours of observation.

Abstract

Experiments that pursue detection of signals from the Epoch of Reionization (EoR) are relying on spectral smoothness of source spectra at low frequencies. This article empirically explores the effect of foreground spectra on EoR experiments by measuring high-resolution full-polarization spectra for the 586 brightest unresolved sources in one of the MWA EoR fields using 45 h of observation. A novel peeling scheme is used to subtract 2500 sources from the visibilities with ionospheric and beam corrections, resulting in the deepest, confusion-limited MWA image so far. The resulting spectra are found to be affected by instrumental effects, which limit the constraints that can be set on source-intrinsic spectral structure. The sensitivity and power-spectrum of the spectra are analysed, and it is found that the spectra of residuals are dominated by PSF sidelobes from nearby undeconvolved sources. We release a catalogue describing the spectral parameters for each measured source.