  We included the intrinsic line profiles of the strongest fluorescent lines in
the X-ray radiative transfer code SKIRT to model the cold-gas structure and
kinematics based on high-resolution line observations from XRISM/Resolve and
Athena/X-IFU. The intrinsic line profiles of the Ka and Kb lines of Cr, Mn, Fe,
Co, Ni, and Cu were implemented based on a multi-Lorentzian parameterisation
and line energies are sampled from these Lorentzian components during the
radiative transfer routine. In the optically thin regime, the SKIRT results
match the intrinsic line profiles as measured in the laboratory. With a more
complex 3D model that also includes kinematics, we find that the intrinsic line
profiles are broadened and shifted to an extent that will be detectable with
XRISM/Resolve; this model also demonstrates the importance of the intrinsic
line shapes for constraining kinematics. We find that observed line profiles
directly trace the cold-gas kinematics, without any additional radiative
transfer effects. With the advent of the first XRISM/Resolve data, this update
to the X-ray radiative transfer framework of SKIRT is timely and provides a
unique tool for constraining the velocity structure of cold gas from X-ray
microcalorimeter spectra.
