SKIRT 9: redesigning an advanced dust radiative transfer code to allow
  kinematics, line transfer and polarization by aligned dust grains
  The open source SKIRT Monte Carlo radiative transfer code has been used for
more than 15 years to model the interaction between radiation and dust in
various astrophysical systems. In this work, we present version 9 of the code,
which has been substantially redesigned to support long-term objectives. We
invite interested readers to participate in the development, testing and
application of new features such as including gas media types in addition to
dust, performing line transfer in addition to continuum radiation transfer, and
modeling polarization by non-spherical dust grains aligned by magnetic fields.
We describe the major challenges involved in preparing the code for these and
other extensions, as well as their resolution, including a completely new
treatment of wavelengths to support kinematics. SKIRT 9 properly runs over 400
handcrafted functional tests and successfully performs all relevant benchmarks.
The source code and all documentation is publicly available for use and ready
for further collaborative development.
