Radiative transfer of energetic photons: X-rays and helium ionization in C 2-Ray
Por:
Friedrich M.M., Mellema G., Iliev I.T., Shapiro P.R.
Publicada:
1 ene 2012
Resumen:
We present an extension to the short-characteristic ray-tracing and non-equilibrium photoionization code C 2-Ray. The new version includes the effects of helium and improved multifrequency heating. The motivation for this work is to be able to deal with harder ionizing spectra, such as from quasar-like sources during cosmic reionization. We review the basic algorithmic ingredients of C 2-Ray before describing the changes implemented, which include a treatment of the full on-the-spot (OTS) approximation, secondary ionization, and multifrequency photoionization and heating. We performed a series of tests against equilibrium solutions from cloudy as well as comparisons to the hydrogen-only solutions by C 2-Ray in the extensive cosmological radiative transfer code comparison project. We show that the full, coupled OTS approximation is more accurate than the simplified, uncoupled one. We find that also with helium and a multifrequency setup, long time-steps (up to ~ 10 percent of the recombination time) still give accurate results for the ionization fractions. On the other hand, accurate results for the temperature set strong constraints on the time-step. The details of these constraints depend, however, on the optical depth of the cells. We use the new version of the code to confirm that the assumption made in many reionization simulations, namely that helium is singly ionized everywhere where hydrogen is, is indeed valid when the sources have stellar-like spectra. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.
Filiaciones:
Friedrich M.M.:
Department of Astronomy, Stockholm University, AlbaNova, SE-106 91 Stockholm, Sweden
The Oskar Klein Centre, Stockholm University, AlbaNova, SE-106 91 Stockholm, Sweden
Mellema G.:
Department of Astronomy, Stockholm University, AlbaNova, SE-106 91 Stockholm, Sweden
The Oskar Klein Centre, Stockholm University, AlbaNova, SE-106 91 Stockholm, Sweden
Iliev I.T.:
Astronomy Centre, Department of Physics and Astronomy, University of Sussex, Pevensey II Building, Falmer, Brighton BN1 9QH, United Kingdom
Shapiro P.R.:
Department of Astronomy, The University of Texas, Austin, TX 78712, United States
Texas Cosmology Center, The University of Texas, Austin, TX 78712, United States
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