Characterizing Low-frequency Foregrounds for Cosmological HI studies with the uGMRT — Indian SKA pathfinder

Understanding the low-frequency radio sky in depth is necessary to mitigate foregrounds in order to detect the redshifted 21 cm signal of neutral hydrogen from the Cosmic Dawn, Epoch of Reionization (EoR) and post-reionization era. Here, we present the detailed analysis of foregrounds in ELAIS N1 field observed with the upgraded Giant Meterwave Radio Telescope (uGMRT) at 300-500 MHz. We show the effects of direction-dependent and direction-independent calibration in the estimation of angular power spectrum (APS) of diffuse galactic synchrotron radiation (DGSE). We have found that the effects of direction-dependent calibration can be ignored with higher tapering of the field of view in comparison with direction-independent calibration. For the first time, we estimated the spectral characteristics of the APS or Multi-Frequency Angular Power Spectrum (MFAPS) of diffuse Galactic synchrotron emission (DGSE) over the wide frequency bandwidth of 200 MHz from radio interferometric observations. We found that the spectral index of APS of DGSE is consistent with previous all-sky measurements by a single dipole antenna. We present a radio source catalog containing 2528 sources and normalized source counts derived from that. The normalized source counts are in agreement with previous observations of the same field, as well as model source counts from the Square Kilometre Array Design Study (SKADS) and T-Recs simulation. It shows a flattening below 1 mJy which corresponds to the rise in population of star forming galaxies and radio-quiet AGNs. We will also present a simple solution to RFI excision in estimation of 21 cm power spectrum. We show with both simulation and observation that we get an unbiased and robust estimate of the power spectrum using the CLEAN algorithm.