Sultan Hassan, Centre for Extragalactic Theory, University of the Western Cape, South Africa
From Instantaneous to Late Reionization
The 21cm emission line is a hyperfine spin-flip transition of neutral hydrogen. Prior to the completion of cosmological reionization, the Universe is expected to have glowed brightly in this transition owing to the ubiquitous presence of tepid neutral hydrogen, with overdense/ neutral regions glowing more brightly and underdense/ionized ones less so. Over the next decade, spatial fluctuations in the 21cm line will be one of the most important cosmological and astrophysical probes of the early universe. The recent low value of the Planck 2016 integrated optical depth to Thomson scattering suggests that reionization occurred more suddenly, and at much later times, than what was previously believed. This will have a significant impact on the expected 21cm signal. Using a semi-numerical framework, I will present two models of reionizations (“Instantaneous” and “Late”) and show how these models can produce different HII bubble sizes which lead to different 21cm power spectra at the same ionisation fraction. Using an MCMC analysis, I will further discuss how our three free parameters (ionising escape fraction (fesc), Amplitude of ionising emissivity (A), emissivity-halo mass power dependence (n)) can be well constrained against the current EoR observations and ongoing/upcoming 21cm EoR experiments, such LOFAR, HERA and SKA.