Lunch talk on Jun. 19, 2023

Radiative Transfer of 21-cm Signals From the Epoch of Reionisation

Speaker: Qin Han (UCL)

Venue: Video Conference

Time: 12:30 PM, Monday, Jun. 19, 2023

Abstract: 

About 10 million years after the Big Bang, the Universe was almost entirely neutral (mostly neutral hydrogen, HI). Later on, luminous sources (e.g. galaxies) formed and produced copious ionising photos. The process of luminous sources gradually drove the Universe to be almost completely ionised is called ‘cosmic reionisation’. Throughout this epoch of reionisation, HI gas is always present. Therefore, the 21-cm line associated with the transition between hyperfine states of HI is a unique probe for the entire epoch. As more and more studies focus on how luminous sources formed and ionised the neutral medium, the production and propagation of the 21-cm signal remains over-simplified in most studies. Predicting accurate 21-cm signal template will be vital for retrieving the details of reionisation from future observational data (e.g. from The Square Kilometre Array, SKA). Hence, we use a covariant radiative transfer treatment which accounts for the local physics (gas properties) and the cosmological effects. The globally-averaged 21-cm signal we calculated is consistent with conventional method. However, we demonstrate that many features imprinted by ionised cavities are missing when using a conventional method and can be accurately predicted by our method. We show that detailed radiative transfer is suitable and necessary for modelling the 21-cm features imprinted by the detailed ionisation and thermal structures of the cavities.

Report PPT:  SWIFAR_Qin Han.pdf