The GMRT Epoch of Reionization experiment: a new upper limit on the neutral hydrogen power spectrum at z≈ 8.6

TLDR

The GMRT‑EoR experiment seeks to detect the 21 cm power spectrum at z≈9, providing constraints on reionization models and the end of the Dark Ages driven by the first UV‑bright sources. This study presents a new upper limit on the 21 cm power spectrum during the Epoch of Reionization, aimed at constraining models with an unheated intergalactic medium. The authors excised radio‑frequency interference using localisation and singular‑value decomposition, modeled foregrounds with a piecewise linear filter, and estimated the power spectrum via cross‑correlations of foreground‑subtracted images. From about 50 hours of GMRT observations in December 2007, the authors derived the new upper limit, tightening constraints on reionization scenarios with a cold IGM.

Abstract

We present a new upper limit to the 21cm power spectrum during the Epoch of Reionization (EoR) which constrains reionization models with an unheated IGM. The GMRT-EoR experiment is an ongoing effort to make a statistical detection of the power spectrum of 21cm neutral hydrogen emission at redshift z~9. Data from this redshift constrain models of the EoR, the end of the Dark Ages arising from the formation of the first bright UV sources, probably stars or mini-quasars. We present results from approximately 50 hours of observations at the Giant Metrewave Radio Telescope in India from December 2007. We describe radio frequency interference (RFI) localisation schemes which allow bright sources on the ground to be identified and physically removed in addition to automated flagging. Singular-value decomposition is used to remove remaining broadband RFI by identifying ground sources with large eigenvalues. Foregrounds are modelled using a piecewise linear filter and the power spectrum is measured using cross-correlations of foreground subtracted images.