Abstract
Abstract
Power spectrum of H i 21-cm radiation is one of the promising probes to study
large scale structure of the universe and understand galaxy formation and evolution. The presence
of foregrounds, that are orders of magnitude larger in the same frequency range of the redshifted
21-cm signal has been one of the largest observational challenges. The foreground contamination
also hinders the calibration procedures and introduces residual calibration errors in the
interferometric data. It has been shown that the calibration errors can introduce bias in the
21-cm power spectrum estimates and introduce additional systematics. In this work, we assess the
efficacy of 21-cm power spectrum estimation for the uGMRT Band-3 observations of the ELAIS-N1
field. We first evaluate the statistics of the residual gain errors and perform additional
flagging based on these statistics. We then use an analytical method to estimate the bias and
variance in the power spectrum. We found that (a) the additional flagging based on calibration
accuracy help reduce the bias and systematics in the power spectrum, (b) the majority of the
systematics at the lower angular scales, ℓ< 6000, are due to the residual gain errors, (c)
for the uGMRT baseline configuration and system parameters, the standard deviation is always
higher than the bias in the power spectrum estimates. Based on our analysis we observe that for an
angular multipole of ℓ∼3000, 2000 hours of `on source time' is required with the uGMRT
to detect redshifted 21-cm signal at 3-σ significance from a redshift of 2.55. In this
work we only consider the power spectrum measurement in the plane of the sky, an assessment of
residual gain statistics and its effect on multifrequency angular power spectrum estimation for
the uGMRT and the SKA like telescopes will be presented in a companion paper.