Solutions for the evolution of the cosmic X-ray background are greatly accelerated if one tabulates the IGM opacity, τν(z, z′), ahead of time (see in Appendix C of Haardt & Madau (1996) for some discussion of this technique). ARES automatically looks in $ARES/input/optical_depth
for τν(z, z′) lookup tables.
The shape of the lookup table is defined by the redshift range being considered (set by the parameters first_light_redshift
and final_redshift
), the number of redshift bins used to sample that interval, tau_redshift_bins
, the minimum and maximum photon energies (pop_Emin
and pop_Emax
), and the number of photon energies (determined iteratively from the redshift and energy intervals and the value of tau_redshift_bins
).
By default, ares generates tables assuming the IGM is fully neutral, but that is not required. To make optical depth tables of your own, see $ARES/input/optical_depth/generate_optical_depth_tables.py
. See Section 3 of Mirocha (2014) for more discussion of this technique.
To generate the table used for the calculations in Mirocha, Furlanetto, & Sun (2017), modify the following lines of $ARES/input/optical_depth/generate_optical_depth_tables.py
:
zf, zi = (5, 50)
Emin = 2e2
Emax = 3e4
Nz = [1e3]
helium = 1
The set of parameters used for these calculations are described in the "Simulations" section of param_bundles
.