Investigating the velocity structure and X-ray observable properties of simulated galaxy clusters with PHOX

Non-thermal motions in the intracluster medium (ICM) are believed to play a non-negligible role in the pressure support to the total gravitating mass of galaxy clusters. Future X-ray missions, such as ASTRO-H and ATHENA, will eventually allow us to directly detect the signature of these motions from high-resolution spectra of the ICM. In this paper, we present a study on a set of clusters extracted from a cosmological hydrodynamical simulation, devoted to explore the role of non-thermal velocity amplitude in characterizing the cluster state and the relation between observed X-ray properties. In order to reach this goal, we apply the X-ray virtual telescope PHOX to generate synthetic observations of the simulated clusters with both Chandra and ATHENA, the latter used as an example for the performance of very high-resolution X-ray telescopes. From Chandra spectra we extract global properties, e. g. luminosity and temperature, and we accurately estimate the gas velocity dispersion along the line of sight achievable from the broadening of emission lines from heavy ions (e.g. Fe) resolved in ATHENA spectra. Given the good agreement found between simulations (true, intrinsic solution) and mock observations (detectable amplitude of non-thermal velocities), we further extend the analysis to the relation between non-thermal velocity dispersion of the gas and the L-X-T scaling law for the simulated clusters. Interestingly, we find a clear dependence of slope and scatter on the selection criterion for the clusters, based on the level of significance of non-thermal motions. Namely, the scatter in the relation is significantly reduced by the exclusion of the clusters, for which we estimate the highest turbulent velocities. Such velocity diagnostics appears therefore as a promising independent way to identify disturbed clusters, in addition to the commonly used morphological inspection.