Multi-frequency angular power spectrum of the 21 cm signal from the Epoch of Reionisation using the Murchison Widefield Array
Context. The Multi-frequency Angular Power Spectrum (MAPS) is an alternative to spherically averaged power spectra, and computes local fluctuations in the angular power spectrum without need for line-of-sight 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 single-frequency 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 large-scale modes prior to MAPS application, significantly reducing MAPS power due to systematics.
Results: The MAPS showed a contrast of 102-103 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 single-frequency angular power spectrum was also computed. At z = 7.5 and l = 200, we found an angular power of 53 mK2, 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 large-scale modes, was the dominant source of systematic power bias. The single-frequency 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.
Astronomy and Astrophysics
- Pub Date:
- October 2022
- instrumentation: interferometers;
- methods: statistical;
- dark ages;
- first stars;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- Astrophysics - Instrumentation and Methods for Astrophysics
- 9 pages, 9 figures