Abstract Details

Name: Janakee Raste
Affiliation: Tata Institute of Fundamental Research
Conference ID: ASI2020_145
Title : Analytical Formalism to Study the 21 cm Signal from Cosmic Dawn and Epoch of Reionization
Authors and Co-Authors : Janakee Raste, Prof. Shiv Sethi (Thesis supervisor)
Abstract Type : Oral
Abstract Category : Thesis
Abstract : The epoch of Cosmic Dawn and Reionization is one of the most important time periods of the universe when first sources of radiation like stars and galaxies were formed, and they changed the properties of their surrounding medium. 21 cm radiation emitted due to the hyperfine splitting of ground state of neutral hydrogen is one of the most important probes to study the state and dynamics of neutral medium during this epoch. Efficient modelling of this signal is essential for inferring physical information from data sets that observatories such as SKA will produce. Numerical simulations of this signal are computationally inefficient as well as limited in dynamic range. Therefore, I will present an analytical formalism to understand the statistical properties of the 21 cm signal of neutral hydrogen from the epoch of reionization and cosmic dawn. In this formalism, we calculate the size distribution of ionization bubbles in the early universe, and the spin temperature profiles around them due to X-rays and Lyman-alpha radiation. Using geometric and probabilistic arguments, we model the fluctuations of ionization, heating and coupling inhomogeneity for a range of modelling parameters. We compute the global 21 cm signal, its auto-correlation and power spectrum in the redshift range 10 < z < 30. This is a computationally inexpensive method, which can be used to compare various reionization, heating, and coupling histories. Comparing results of this formalism with simulations would lead to a deeper understanding of the properties of the first sources, as well as point out the strengths and weaknesses of different methods.