Disentangling Resonant Scattering and Gas Motions in Galaxy Cluster Emission Line Profiles

Future high spectral resolution telescopes will enable us to place tight constraints on turbulence in the intra-cluster medium through the line widths of strong emission lines. At the same time, these bright lines are the most prone to be optically thick. This requires us to separate the effects of resonant scattering from turbulence, both of which could broaden the lines. How this can be achieved has yet not been quantitatively addressed. In this paper, we propose a flexible new parametrization for the line profile, which allows these effects to be distinguished. The model has only 3 free parameters, which we calibrate with Monte-Carlo radiative transfer simulations. We provide fitting functions and tables that allow the results of these calculations to be easily incorporated into a fast spectral fitting package. In a mock spectral fit, we explicitly show that this parameterization allows us to correctly estimate the turbulent amplitude and metallicity of a cluster such as Perseus, which would otherwise give significantly biased results. We also show how the physical origin of the line shape can be understood analytically.