CRASH: A radiative transfer scheme

A. Maselli, A. Ferrara, B. Ciardi

Research output: Contribution to journalArticlepeer-review


We present a largely improved version of CRASH, a 3D radiative transfer code that treats the effects of ionizing radiation propagating through a given inhomogeneous H/He cosmological density field on the physical conditions of the gas. The code, based on a Monte Carlo technique, self-consistently calculates the time evolution of gas temperature and ionization fractions due to an arbitrary number of point/extended sources and/or diffuse background radiation with given spectra. In addition, the effects of diffuse ionizing radiation following recombinations of ionized atoms have been included. After a complete description of the numerical scheme, to demonstrate the performance, accuracy, convergence and robustness of the code, we present four different test cases designed to investigate specific aspects of radiative transfer: (i) a pure-hydrogen isothermal Strömgren sphere; (ii) realistic Strömgren spheres; (iii) multiple overlapping point sources; and (iv) shadowing of background radiation by an intervening optically thick layer. When possible, detailed quantitative comparison of the results against either analytical solutions or ID standard photoionization codes has been made, and shows a good level of agreement. For more complicated tests the code yields physically plausible results, which could be eventually checked only by comparison with other similar codes. Finally, we briefly discuss future possible developments and cosmological applications of the code.

Original languageEnglish
Pages (from-to)379-394
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - Oct 21 2003


  • Cosmology: theory
  • Intergalactic medium
  • Methods: numerical
  • Radiative transfer

ASJC Scopus subject areas

  • Space and Planetary Science


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