Improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at z ≈ 9.1 from LOFAR

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Date

2020

Journal Title

Journal ISSN

Volume Title

Publisher

Oxford University Press

Abstract

A new upper limit on the 21 cm signal power spectrum at a redshift of z ≈ 9.1 is presented, based on 141 h of data obtained with the Low-Frequency Array (LOFAR). The analysis includes significant improvements in spectrally smooth gain-calibration, Gaussian Process Regression (GPR) foreground mitigation and optimally weighted power spectrum inference. Previously seen ‘excess power’ due to spectral structure in the gain solutions has markedly reduced but some excess power still remains with a spectral correlation distinct from thermal noise. This excess has a spectral coherence scale of 0.25–0.45 MHz and is partially correlated between nights, especially in the foreground wedge region.

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Keywords

Methods: data analysis, Techniques: interferometric, Dark ages, Reionization, Cosmology: observations, First stars

Citation

Ghosh, A. et al. (2020). Improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at z ≈ 9.1 from LOFAR. Monthly Notices of the Royal Astronomical Society, 493(2), 1662–1685