Reionization by UV or X-ray sources

S. Baek^1,2, B. Semelin^1,3, P. Di Matteo⁴, Y. Revaz⁵ and F. Combes¹

¹ LERMA, Observatoire de Paris, 61 Av. de l’Observatoire, 75014 Paris, France
² Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
e-mail: sunghye.baek@sns.it
³ Université Pierre et Marie Curie, 4 place Jussieu, 75005 Paris, France
⁴ GEPI, Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon Cedex, France
⁵ Laboratoire d’Astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), Swizerland

Received: 3 March 2010
Accepted: 3 August 2010

Abstract

We present simulations of the 21-cm signal during the epoch of reionization. We focus on properly modeling the absorption regime in the presence of inhomogeneous Wouthuysen-Field effect and X-ray heating. We ran radiative transfer simulations for three bands in the source spectrum (Lyman, UV, and X-ray) to fully account for these processes. We find that the brightness temperature fluctuation of the 21 cm signal has an amplitude greater than 100 mK during the early reionization, up to 10 times greater than the typical amplitude of a few 10 mK obtained during the later emission phase. More importantly, we find that even a rather high contribution from QSO-like sources only damps the absorption regime without erasing it. Heating the IGM with X-ray takes time. Our results show that observations of the early reionization will probably benefit from a higher signal-to-noise value than during later stages. After analyzing the statistical properties of the signal (power spectrum and PDF) we find three diagnostics to constrain the level of X-ray, hence the nature of the first sources.