Thursday, February 25 2021
16:00 - 17:30

IMSc Webinar

Probing the early Universe using cosmological 21-cm signal; google meet link:

Rajesh Mondal

Stockholm University

Google meet link:

Cosmology is the study of the Universe as a whole. The first billion years of cosmic history of the Universe mark the formation of the first stars and galaxies. The appearance of these first sources of light set in motion many lasting changes. Perhaps the most important one was the transition of essentially all normal matter in the Universe from a cold and atomic state to a hot and ionized one, an event known as Epoch of Reionization. This epoch holds the key to unlocking many of the remaining mysteries in cosmology, astrophysics, and physics. However, as yet, there is very limited observational information available in this field of research. After decades of being a subject of theoretical interest, recently reionization became a topic of direct observational studies, for which groundbreaking international projects that span the electromagnetic spectrum are soon to come online, e.g. SKA, HERA, REACH, JWST, TMT, LSST, etc. Among these several international Mega Science Projects, India is a founding member and major partner in SKA and TMT. The wealth of data from these experiments will address the following fundamental questions: How did the first cosmic structures form and evolve? When and where were the first stars and Galaxies born? What were the nature and the exact role of the first sources of ionization? What was the role of Dark matter at early times? One observational probe which can answer most questions related to reionization is a radio signal produced by neutral atomic hydrogen in the Universe, with the rest-frame wavelength of about 21 cm. Due to the expansion of the Universe, signals from earlier times reach us at longer wavelengths. This implies that in principle we can follow the disappearance of atomic hydrogen due to reionization by tuning into the specific expected stretched wavelength of the radio signal over a wide range of wavelengths. However, to discover what happened during reionization, we need to `model' this signal very accurately, and `decode' the signals in terms of model parameters that describe the cosmology and astrophysical processes. I will describe some of the most exciting frontiers in current studies of the Epoch of Reionization.

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