Observing GAMA-23 field with uGMRT band-2

Abstract

The GAMA-23 field is a promising region for studying the Epoch of Reionization (EoR), a key phase in the evolution of the Universe when the first luminous sources ionized the intergalactic medium (IGM). Thanks to its extensive multi-wavelength coverage and accessibility to low-frequency radio observations, GAMA-23 allows for detailed investigations of the 21 cm signal, which traces neutral hydrogen in the early Universe. In this thesis, we used data from the upgraded Giant Metrewave Radio Telescope (uGMRT) in Band-2 (120–250 MHz) to detect faint radio signals and im- prove our understanding of ionization and galaxy formation during cosmic history. Due to heavy radio frequency interference (RFI) caused by the low elevation of the source from the GMRT site, the legacy GMRT software backend (GSB) data was unusable. Instead, we used data from the GMRT Wideband Backend (GWB), which we split into sub-bands and processed using the SPAM pipeline. SPAM includes both direction-independent and direction-dependent calibration, and it corrects for ionospheric phase errors using the peeling technique. A TGSS-based sky model was used as a refer- ence during the calibration. After calibrating the individual sub-bands, we used WSClean for wideband imaging, which resulted in a high-resolution image with an off-source RMS noise of 316 μJy/beam and a resolution of 15.35”× 8.22”. We then performed source detection and created a source catalog, which was cross-matched with several existing radio surveys (TGSS, NVSS, SUMSS, RACS ,and GLEAM) to check for positional accuracy and flux consistency. The comparison showed good agreement with previous surveys, indicating that our calibration and imaging were successful. We also calculated differ- ential sourcecountsat183 MHz, correcting for false detections and incom-pleteness using simulations. The source counts match well with predictions from models like S3-SKADS and T-RECS, as well as previous observational results. Overall, the results of this work add to our understanding of faint radio sources, star formation, and the evolution of galaxies in the early Universe.