This is the home page of the cosmological radiative transfer code CRASH. Here you can find a description of its main features, references to the scientific papers describing it in detail, applications, simulation outputs, figures, movies and more!

CRASH is a monte carlo radiative transfer code mainly developed for cosmological studies, though its very general implementations of the different physical processes involved makes its suited to a wide variety of astrophysical application.

Code development history

The very first version of the code has been implemented in 2001 as part of one of the first study of the process of cosmological reionization, and has been described in Sec. 4 of the paper "Cosmological reionization around the first stars: Monte Carlo radiative transfer" by B. Ciardi, A. Ferrara, S. Marri, and G. Raimondo (Ciardi et al. 2001, MNRAS, 324, 381). In this first layout, the main basic conceptual and structural features have been implemented. The radiative transfer code was developed as a ray tracing scheme where radiation is dicretized and represented by monochromatic photon packets travelling along rays and interacting with the gas represented on a 3D Cartesian grid.Thanks to the Monte Carlo sampling of the absorption probability, yet in its first layout the code could be applied to a variety of quite general configurations being able to deal with (i) arbitrary 3D density fields, (ii) multiple point sources, (iii) arbitrary source spectra and angular emissivity distributions, and (iv) treating self consistently the ionizing radiation resulting from hydrogen recombination. Despite this high level of flexibility, the code at this stage, followed exclusively the evolution of the ionization state of hydrogen without solving the energy balance. Changes in the temperature due to the process of photo-heating, were approximated instead by manually setting the temperature of regions ionized above a given treshold, to a fixed value about 10^4 K, characteristic value for an ionized gas.

The approximation done on the thermal state of the gas is a good one for studying e.g. the main phases through which the process of reionization evolves, but starts to be quite pour in studies focused on the modelling of the physical state of the intergalactic medium (IGM), observed in the Lyman alpha forest. This has been the main trigger to the development of a new version of the code, based on a much more sofisticated implementation, described in detail in the paper " CRASH: a radiative transfer scheme" by A. Maselli, A. Ferrara & B. Ciardi (Maselli et al, 2003, 345, 379).

Implementation description


Comparison Project tests

CRASH vs CLOUDY comparison

Errata corrige

Photons Redistribution


UVB background Fluctuations
Quasar Proximity Regions

Topic revision: r9 - 21 Sep 2009, AntonellaMaselli
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