Title:	Probing early Universe through redshifted 21-cm signal: Modeling and observational challenges
Authors:	Shaw, Abinash Kumar Chakraborty, Arnab Kamran, Mohd Ghara, Raghunath Choudhuri, Samir Ali, Sk. Saiyad Pal, Srijita Ghosh, Abhik Kumar, Jais Dutta, Prasun Sarkar, Anjan Kumar
Issue Date:	20-Jan-2023
Publisher:	Indian Academy of Sciences
Citation:	Journal of Astrophysics and Astronomy, 2023, Vol.44, p4
Abstract:	Cosmic dawn (CD) and the epoch of reionization (EoR) are the most important parts of cosmic history during which the first luminous structures emerged. These first objects heated and ionized the neutral atomic hydrogen in the intergalactic medium. The redshifted 21-cm radiation from the atomic hydrogen provides an excellent direct probe to study the evolution of neutral hydrogen (Hi) and thus reveal nature of the first luminous objects, their evolution and role in this last phase transition of the Universe and formation and evolution of the structures thereafter. Direct mapping of the Hi density during the CD–EoR is rather difficult with the current and forthcoming instruments due to stronger foreground and other observational contamination. The first detection of this redshifted Hi signal is expected to be done through statistical estimators. Given the upmost importance of the detection and analysis of the redshifted 21-cm signal, physics of CD–EoR is considered as one of the objective of the upcoming SKA-low telescope. This paper summarizes the collective effort of Indian astronomers to understand the origin of the redshifted 21-cm signal, sources of first ionizing photons, their propagation through the IGM, various cosmological effects on the expected 21-cm signal, various statistical measures of the signal like power spectrum, bispectrum, etc. A collective effort on detection of such signal by developing estimators of the statistical measures with rigorous assessment of their expected uncertainties, various challenges like that of the large foreground emission and calibration issues are also discussed. Various versions of the detection methods discussed here have also been used in practice with the Giant Meterwave Radio Telescope with successful assessment of the foreground contamination and upper limits on the matter density in reionization and post-reionization era. The collective efforts compiled here has been a large part of the global effort to prepare proper observational technique, analysis procedure for the first light of the CD–EoR through the SKA-low.
Description:	Open Access from Indian Academy of Sciences
URI:	http://hdl.handle.net/2289/8044
ISSN:	0250-6335 0973-7758 (Online)
Alternative Location:	https://ui.adsabs.harvard.edu/abs/2023JApA...44....4S/abstract https://arxiv.org/abs/2211.05512 https://inspirehep.net/literature/2180556 https://doi.org/10.1007/s12036-022-09889-6
Copyright:	2023 Indian Academy of Sciences
Appears in Collections:	Research Papers (A&A)

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