Prospects for Detecting the 326.5 MHz Redshifted 21-cm HI Signal with the Ooty Radio Telescope (ORT)

Abstract

Observations of the redshifted 21 cm HI fluctuations promise to be an important probe of the post-reionization era. In this paper we calculate the expected signal and foregrounds for the upgraded Ooty Radio Telescope (ORT) which operates at frequency =326.5 MHz which corresponds to redshift z=3.35. Assuming that the visibilities contain only the HI signal and system noise, we show that a 3 sigma detection of the HI signal ~ 1 mk is possible at angular scales 11 arc-minutes to 3 degree with ~ 1000 hours of observation. Foreground removal is one of the major challenges for a statistical detection of the redshifted 21 cm HI signal. We assess the contribution of different foregrounds and find that the 326.5 MHz sky is dominated by the extragalactic point sources at the angular scales of our interest. The expected total foregrounds are 4-5 orders of magnitude higher than the HI signal.