Towards 21-cm intensity mapping at z = 2.28 with uGMRT using the tapered gridded estimator � IV. Wide-band analysis

Abstract

We present a Wide-band tapered gridded estimator (TGE), which incorporates baseline migration and variation of the primary beam pattern for neutral hydrogen (H i) 21-cm intensity mapping (IM) with large frequency bandwidth radio-interferometric observations. Here we have analysed 394 ? 494 MHz (z = 1.9�2.6) uGMRT data to estimate the Multifrequency Angular Power Spectrum (MAPS) C?(??) from which we have removed the foregrounds using the polynomial fitting (PF) and Gaussian Process Regression (GPR) methods developed in our earlier work. Using the residual C?(??) to estimate the mean-squared 21-cm brightness temperature fluctuation ?2(k), we find that this is consistent with 0 � 2? in several k bins. The resulting 2? upper limit ?2(k) &lt

(4.68)2 mK2 at k = 0.219 Mpc?1 is nearly 15 times tighter than earlier limits obtained from a smaller bandwidth (24.4 MHz) of the same data. The 2? upper limit [?H ibH i] &lt

1.01 � 10?2 is within an order of magnitude of the value expected from independent estimates of the H i mass density ?H i and the H i bias bHi. The techniques used here can be applied to other telescopes and frequencies, including ? 150 MHz Epoch of Reionization observations. � 2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.