Research Projects

The Epoch of Reionization (EoR) and Cosmic Dawn (CD) mark the birth of the first galaxies and quasars in ushering the universe from darkness into light. Despite their importance, these epochs remain poorly understood due to the difficulty in observing the faint early-universe sources. Key questions—such as the timing and properties of the first luminous sources, the morphology of ionized regions, and the evolution of neutral hydrogen—are still open. Among the most promising observational probes of these epochs is the redshifted HI 21-cm line, which traces the distribution and thermal state of neutral hydrogen. Ongoing experiments like the uGMRT (India), MWA, and LOFAR have already placed upper limits on the HI 21-cm power spectrum. The upcoming Square Kilometre Array (SKA)—one of the most sensitive and promising radio telescopes under construction, with India as a full member—is expected to transform this field by enabling detailed detection and characterization of the HI 21-cm signal. In this context, the proposed project aims to advance our understanding of the first luminous sources and their impact on the intergalactic medium through two complementary research directions. First, we propose to study the detection of ionized bubbles around known bright galaxies and quasars using a matched filter technique. Unlike the conventional approach of measuring the power spectrum, this method focuses on enhancing the detectability of individual features in the 21-cm maps by optimally combining the weak signal, significantly improving the signal-to-noise ratio. To implement this, we will develop an end-to-end simulation pipeline that generates realistic mock visibility data, incorporating the HI 21-cm signal, astrophysical foregrounds, system noise, and calibration errors tailored to instruments like the uGMRT and SKA-Low. After validation, we will apply this pipeline to actual uGMRT observations. Second, we aim to investigate the non-Gaussian features of the HI 21-cm signal during cosmic dawn through bispectrum analysis. The bispectrum encodes crucial information about the morphology and correlations in the signal that are not captured by the power spectrum alone. In particular, we will explore the impact of large HI optical depth, which can arise due to low spin temperature and high-density conditions during cosmic dawn, and is often neglected in conventional models. A detailed theoretical and numerical study will be conducted to assess their effects on the signal and their implications for detection strategies with future instruments like SKA. Upon successful completion, the project is expected to yield a validated detection methodology for ionized bubbles using the matched filter approach, an end-to-end simulation and analysis pipeline that can be applied to current and future 21-cm experiments, and theoretical insights into non-Gaussian features in the HI signal, especially under high optical depth conditions. These results will hold the potential to support upcoming SKA- Low observations directly and contribute significantly to global efforts aimed at uncovering the nature of the first galaxies and the evolution of the early universe.