Abstract Details

Name: Aritra Kundu
Affiliation: Presidency University, Kolkata
Conference ID: ASI2021_143
Title : Cosmic recombination history in light of EDGES measurements of the cosmic dawn 21-cm signal
Authors and Co-Authors : Aritra Kundu (Presidency University, Kolkata), Kanan Kumar Datta (Presidency University, Kolkata), Ankit Paul (Presidency University, Kolkata) and Ankita Bera (Presidency University, Kolkata)
Abstract Type : Oral
Abstract Category : General Relativity and Cosmology
Abstract : Cosmic Dawn is one of the most important epoch in the early Universe, which can be studied using the hydrogen 21-cm line. The recent EDGES measurements of the global 21-cm signal from the cosmic dawn suggest a possibility of the kinetic temperature of the inter-galactic medium (IGM) being significantly lower compared to its expected value. The colder IGM directly affects the hydrogen recombination of the universe during the cosmic dawn and dark ages by enhancing the rate of recombinations. Here, we study and quantify, the impact of the colder IGM scenario on the recombination history of the universe in the context of dark matter-baryon interaction model which is widely used to explain the depth of the EDGES 21-cm signal. We find that, in general, the hydrogen ionization fraction gets suppressed during the dark ages and cosmic dawn and the suppression gradually increases at lower redshifts until X-ray heating from the first stars turns on. However, accurate estimation of the ionisation fraction requires knowledge of the entire thermal history of the IGM, from the epoch of thermal decoupling of hydrogen gas and the CMBR to the cosmic dawn. It is possible that two separate scenarios which predict very similar HI differential temperature during the cosmic dawn and are consistent with the EDGES 21-cm signal might have very different IGM temperature during the dark ages. The evolution of the ionization fraction in these two scenarios are quite different. This prohibits us to accurately calculate the ionization fraction during the cosmic dawn using the EDGES 21-cm signal alone. We find that the changes in the ionization fraction w.r.t the standard scenario at redshift z ∼ 17 could be anything between ∼ 0% to ∼ 36%. This uncertainty may be reduced if measurements of HI 21-cm differential temperature at multiple redshifts are simultaneously used.