A Tapered Gridded Estimator (TGE) for the multifrequency angular power spectrum (MAPS) and the cosmological H I 21-cm power spectrum

In this work, we present a new approach to estimate the power spectrum P(k) of redshifted H I 21-cm brightness temperature fluctuations. The MAPS C-l (nu(a) ,nu(b)) completely quantifies the second-order statistics of the sky signal under the assumption that the signal is statistically homogeneous and isotropic on the sky. Here, we generalize an already existing visibility based estimator for C-l, namely TGE, to develop an estimator for C-l(nu(a) , nu(b)) . The 21-cm power spectrum is the Fourier transform of C-l(Delta nu) with respect to Delta nu = vertical bar nu(a) - nu(b)vertical bar, and we use this to estimate P(k). Using simulations of 150 MHz GMRT observations, we find that this estimator is able to recover P(k) with an accuracy of 5-20 per cent over a reasonably large k range even when the data in 80 per cent randomly chosen frequency channels are flagged.