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

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Abstract: The 21 cm emission of neutral hydrogen is the most promising probe of theepoch of reionizationEoR. In the next few years, the SKA pathfinders willprovide statistical measurements of this signal. Numerical simulationspredicting these observations are necessary to optimize the design of theinstruments. The main difficulty is the computation of the spin temperature ofneutral hydrogen which depends on the gas kinetic temperature and on the levelof 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 laterin the history as long as the sources of X-rays are too weak to heat theintergalactic medium significantly. This work presents the first EoR numericalsimulations including, beside dynamics and ionizing continuum radiativetransfer, a self-consistent treatment of the Ly-alpha radiative transfer. Thisallows us to compute the spin temperature more accurately. We use two differentbox sizes, 20 Mpc-h and 100 Mpc-h, and a star source model. Using the redshiftdependence of average quantities, maps, and power spectra, we quantify theeffect of using different assumptions to compute the spin temperature and theinfluence of the box size. The first effect comes from allowing for a signal inabsorption. The magnitude of this effect depends on the amount of heating byhydrodynamic shocks and X-rays in the intergalactic mediumIGM. The secondeffects comes from using the real, local, Lyman-alpha flux. This effect isimportant for an average ionization fraction of less than 10%: it changes theoverall amplitude of the 21 cm signal, and adds its own fluctuations to thepower spectrum.

Author: S. Baek, P. Di Matteo, B. Semelin, F. Combes, Y. Revaz


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