Multifrequency angular power spectrum of the 21 cm signal from the Epoch of Reionisation using the Murchison Widefield Array
Abstract
Context. The Multifrequency Angular Power Spectrum (MAPS) is an alternative to spherically averaged power spectra, and computes local fluctuations in the angular power spectrum without need for lineofsight spectral transform.
Aims: We aimed to test different approaches to MAPS and treatment of the foreground contamination, and compare with the spherically averaged power spectrum, and the singlefrequency angular power spectrum.
Methods: We applied the MAPS to 110 h of data in z = 6.2 − 7.5 obtained for the Murchison Widefield Array Epoch of Reionisation experiment to compute the statistical power of 21 cm brightness temperature fluctuations. In the presence of bright foregrounds, a filter was applied to remove largescale modes prior to MAPS application, significantly reducing MAPS power due to systematics.
Results: The MAPS showed a contrast of 10^{2}10^{3} to a simulated 21 cm cosmological signal for spectral separations of 0−4 MHz after application of the filter, reflecting results for the spherically averaged power spectrum. The singlefrequency angular power spectrum was also computed. At z = 7.5 and l = 200, we found an angular power of 53 mK^{2}, exceeding a simulated cosmological signal power by a factor of one thousand. Residual spectral structure, inherent to the calibrated data, and not spectral leakage from largescale modes, was the dominant source of systematic power bias. The singlefrequency angular power spectrum yielded slightly poorer results compared with the spherically averaged power spectrum, having applied a spectral filter to reduce foregrounds. Exploration of other filters may improve this result, along with consideration of wider bandwidths.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 October 2022
 DOI:
 10.1051/00046361/202244024
 arXiv:
 arXiv:2208.06082
 Bibcode:
 2022A&A...666A.106T
 Keywords:

 instrumentation: interferometers;
 methods: statistical;
 dark ages;
 reionization;
 first stars;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 9 pages, 9 figures