Simulating the Epoch of Reionization: A Comparison between Radiative Transfer and Semi-Numerical Techniques

by Dr Suman Majumdar (Indian Institute of Technology Indore)

Friday 27 Sept 2013, 10:30 → 11:30 Europe/Stockholm

FA31

Until today, much of the Epoch of Reionization, the period during which most of the hydrogen in the Universe was transformed from neutral (HI) to ionized (HII), remains unknown. Thus numerical simulations are necessary to interpret the observational data, such as the expected redshifted HI 21 cm signal from this epoch. Proper radiative transfer simulations are capable of predicting the HI 21 cm signal very accurately. Unfortunately these simulations are computationally extremely expensive. On the other hand, semi-numerical simulations are computationally fast and capable of generating several realizations of the EoR at the expense of reasonable amount of computational resources. However, the included physics in this case are more approximate. We present here a detailed comparison between a radiative transfer simulation (C2RAY) and a set of semi-numerical simulations developed by us. This comparison is two fold in nature. First we quantify the similarities and differences between these simulations in terms of the morphology of the ionization maps, which are the first basic output from these simulations. This has been done by estimating the bubble size distribution, the topology (i.e. the Euler characteristic), power spectra of the ionization field and cross-correlations between the C2RAY and semi-numerical simulation outputs. Next we compare some observable quantities that would be of interest for the present and upcoming low frequency radio interferometrs like the GMRT, LOFAR, SKA etc. We first consider the variance of the redsifted 21 cm brightness temperature fluctuations. Next, we conisder the redshift space angle averaged 3D power spectrum of the redshifted 21 cm signal and at last we consider the various angular multipoles of the redshift space 3D power spectrum.