The simulated 21 cm signal during the epoch of reionization : full modeling of the Ly-alpha pumping

TL;DR

This paper presents advanced simulations of the 21 cm signal during the epoch of reionization, incorporating a self-consistent treatment of Lyman-alpha radiative transfer to improve accuracy in modeling the spin temperature and its effects.

Contribution

It introduces the first EoR simulations that include detailed Lyman-alpha radiative transfer, enhancing the realism of 21 cm signal predictions.

Findings

Allowing for absorption signals significantly impacts the predicted 21 cm signal.

Local Lyman-alpha flux influences the amplitude and fluctuations of the 21 cm power spectrum.

Box size effects are analyzed to understand their impact on simulation results.

Abstract

The 21 cm emission of neutral hydrogen is the most promising probe of the epoch of reionization(EoR). In the next few years, the SKA pathfinders will provide statistical measurements of this signal. Numerical simulations predicting these observations are necessary to optimize the design of the instruments. The main difficulty is the computation of the spin temperature of neutral hydrogen which depends on the gas kinetic temperature and on the level of the local Lyman-alpha flux. A T_s >> T_cmb assumption is usual. However, this assumption does not apply early in the reionization history, or even later in the history as long as the sources of X-rays are too weak to heat the intergalactic medium significantly. This work presents the first EoR numerical simulations including, beside dynamics and ionizing continuum radiative transfer, a self-consistent treatment of the Ly-alpha radiative transfer. This allows us to compute the spin temperature more accurately. We use two different box sizes, 20 Mpc/h and 100 Mpc/h, and a star source model. Using the redshift dependence of average quantities, maps, and power spectra, we quantify the effect of using different assumptions to compute the spin temperature and the influence of the box size. The first effect comes from allowing for a signal in absorption. The magnitude of this effect depends on the amount of heating by hydrodynamic shocks and X-rays in the intergalactic medium(IGM). The second effects comes from using the real, local, Lyman-alpha flux. This effect is important for an average ionization fraction of less than 10%: it changes the overall amplitude of the 21 cm signal, and adds its own fluctuations to the power spectrum.