Fast large volume simulations of the 21-cm signal from the reionization and pre-reionization epochs

Abstract

While limited to low spatial resolution, the next‐generation low‐frequency radio interferometers that target 21‐cm observations during the era of reionization and prior will have instantaneous fields of view that are many tens of deg2 on the sky. Predictions related to various statistical measurements of the 21‐cm brightness temperature must then be pursued with numerical simulations of reionization with correspondingly large volume box sizes, of the order of 1000 Mpc on one side. We pursue a semi‐numerical scheme to simulate the 21‐cm signal during and prior to reionization by extending a hybrid approach where simulations are performed by first laying down the linear dark matter density field, accounting for the non‐linear evolution of the density field based on second‐order linear perturbation theory as specified by the Zel'dovich approximation, and then specifying the location and mass of collapsed dark matter haloes using the excursion‐set formalism. The location of ionizing sources and the time evolving distribution of ionization field is also specified using an excursion‐set algorithm. We account for the brightness temperature evolution through the coupling between spin and gas temperature due to collisions, radiative coupling in the presence of Lyman α photons and heating of the intergalactic medium, such as due to a background of X‐ray photons. The hybrid simulation method we present is capable of producing the required large volume simulations with adequate resolution in a reasonable time, so a large number of realizations can be obtained with variations in assumptions related to astrophysics and background cosmology that govern the 21‐cm signal.

The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization

“…Bouwens et al 2012;Robertson et al 2013), semi-analytic modelling of reionization (e.g. Choudhury et al 2009;Pritchard et al 2010;Santos et al 2010;Mesinger et al 2011;Raskutti et al 2012;Mitra et al 2013;Shull et al 2012) and numerical simulations of reionization (e.g. Iliev et al 2006; Trac & Cen 2007;Ciardi et al 2012).…”

Probing the first galaxies with the Square Kilometer Array

“…Numerical simulations, on the other hand, can provide a self-consistent treatment of the Lyα radiative transfer, taking into account effects such as the scattering in the Lyα line wings (Semelin et al 2007;Baek et al 2009), although they are typically slow to run and are limited to small volumes (≤100 Mpc/h). Recent developments using seminumerical algorithms have allowed the rapid generation of the high redshift 21 cm signal during the pre-reionization epoch (Santos et al 2008(Santos et al , 2010Mesinger et al 2010) in large boxes, while maintaining the 3-d structure of the signal on large scales as seen in the full numerical simulations.…”

“…In this paper we will generate fast simulations as described in Santos et al (2010) to analyze the dependence of the overall 21 cm signal on several parameters related to the first galaxies in the Universe and consider the ability of an experiment like SKA to constrain these parameters. The layout of this paper is as follows.…”

Linear perturbation theory of reionization in position space: Cosmological radiative transfer along the light cone

“…In fact, because of this, the LPTR can serve as the basis of a semi-numerical simulation algorithm 8 , which can efficiently generate 3D realizations of H II distributions, in a similar spirit to semi-numerical codes [7][8][9][10] based on the ESMR (Mao et al in prep. ).…”

“…[6] and subsequently developed as the basis of several "semi-numerical" simulation codes [7][8][9][10]. These ESMR-based semi-numerical algorithms have been shown to agree well with full radiative transfer simulations for the simplest models of reionization [11,12].…”