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Title: Detecting the 21 cm signal from the Epoch of Reionization using Drift Scans
Authors: Patwa, Akash Kumar
Thesis Advisor: Sethi, Shiv
Subject: Astronomy and Astrophysics
Issue Date: Nov-2020
Publisher: Raman Research Institute, Bengaluru
Citation: Ph.D. Thesis, Jawaharlal Nehru University, New Delhi, 2020
Abstract: In the early universe there are two major transitions in the state of the baryonic matter: recombination and reionization. From the last scattering surface of the cosmic microwave background (CMB) photons we know that the recombination of primordial hydrogen took place at the redshift of z ' 1100. On the other hand, the reionization process is expected to have occurred in the redshift range 10 & z & 6. However, the physical processes responsible for the reionization are poorly constrained. In the recent years there have been multiple efforts to directly probe the cosmic dawn (CD) and epoch of reionization (EoR) with redshifted 21 cm signal of the neutral hydrogen (HI) using radio telescopes designed to operate at low frequencies (50 MHz < n < 200 MHz) (e.g. uGMRT, MWA, HERA, and LOFAR). Measurement of 21 cm signal (also known as HI signal) from EoR is expected to tightly constrain various cosmological and astrophysical phenomena including the formation and growth of large-scale structures, properties of underlying dark matter distribution and first luminous sources (stars and galaxies). According to current theoretical models, the strength of the 21 cm signal (10 mK at z ' 8) is at least three to four orders of magnitude weaker than the foregrounds (300 K) at 150 MHz. The major component of the foregrounds are extragalactic point-like radio sources and diffuse galactic emission. These foregrounds are spectrally smooth unlike the 21 cm signal. This discriminator is used to isolate the 21 cm signal from bright foregrounds.
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