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Ionisation fronts and their interaction with density fluctuations: implications for reionisation

Published online by Cambridge University Press:  06 October 2005

Ilian T. Iliev
Affiliation:
Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8, Canada, email: iliev@cita.utoronto.ca
Paul R. Shapiro
Affiliation:
Department of Astronomy, University of Texas, Austin, 78712, USA
Evan Scannapieco
Affiliation:
Kavli Institute for Theoretical Physics, Kohn Hall, UC Santa Barbara, Santa Barbara, CA 93106, USA
Garrelt Mellema
Affiliation:
ASTRON, P.O. Box 1, NL-7990 AA Dwingeloo, The Netherlands
Marcelo Alvarez
Affiliation:
Department of Astronomy, University of Texas, Austin, 78712, USA
Alejandro C. Raga
Affiliation:
Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de México (UNAM), Apdo. Postal 70-543, 04510 México, D. F., México
Ue-Li Pen
Affiliation:
Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8, Canada, email: iliev@cita.utoronto.ca
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Abstract

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The propagation of cosmological ionisation fronts (I-fronts) during reionisation is strongly influenced by small-scale structure. Here we summarise our recent attempts to understand the effect of this small-scale structure. We present high resolution cosmological N-body simulations at high-z ($z>6$) which resolve a wide range of halo mass, from mini-halos to clusters of large, rare halos. We also study how mini-halos affect I-fronts, through simulations of mini-halo photo-evaporation including numerical gas dynamics with radiative transfer. Furthermore, we modify the I-front propagation equations to account for evolving small-scale structure, and incorporate these results into a semi-analytical reionisation model. When intergalactic medium clumping and mini-halo clustering around sources are included, small-scale structure affects reionisation by slowing it down and extending it in time. This helps to explain the observations of the Wilkinson Microwave Anisotropy Probe, which imply an early and extended reionisation epoch. We also study how source clustering affects the evolution and size of H II regions, finding, in agreement with simulations, that H II regions usually expand, and rarely shrink. Hence, “relic H II regions” are an exception, rather than the rule. When the suppression of small-mass sources in already-ionised regions by Jeans-mass filtering is accounted for, H II regions are smaller, delaying overlap. We also present a new numerical method for radiative transfer which is fast, efficient and easily coupled to hydrodynamics and N-body codes, along with sample tests and applications.

Type
Contributed Papers
Copyright
© 2005 International Astronomical Union