Enabling Radiative Transfer on AMR grids in CRASH
  We introduce CRASH-AMR, a new version of the cosmological Radiative Transfer
(RT) code CRASH, enabled to use refined grids. This new feature allows us to
attain higher resolution in our RT simulations and thus to describe more
accurately ionisation and temperature patterns in high density regions. We have
tested CRASH-AMR by simulating the evolution of an ionised region produced by a
single source embedded in gas at constant density, as well as by a more
realistic configuration of multiple sources in an inhomogeneous density field.
While we find an excellent agreement with the previous version of CRASH when
the AMR feature is disabled, showing that no numerical artifact has been
introduced in CRASH-AMR, when additional refinement levels are used the code
can simulate more accurately the physics of ionised gas in high density
regions. This result has been attained at no computational loss, as RT
simulations on AMR grids with maximum resolution equivalent to that of a
uniform cartesian grid can be run with a gain of up to 60% in computational
time.
