Radial profile and log-normal fluctuations of intra-cluster medium as an   origin of systematic bias of spectroscopic temperature
  The origin of the recently reported systematic bias in the spectroscopic temperature of galaxy clusters is investigated using cosmological hydrodynamical simulations. We find that the local inhomogeneities of the gas temperature and density, after corrected for the global radial profiles, have nearly a universal distribution that resembles the log-normal function. Based on this log-normal approximation for the fluctuations in the intra-cluster medium, we develop an analytical model that explains the bias in the spectroscopic temperature discovered recently. We conclude that the multi-phase nature of the intra-cluster medium not only from the radial profiles but also from the local inhomogeneities plays an essential role in producing the systematic bias. 
Hajime Kawahara, Yasushi Suto, Tetsu Kitayama, Shin Sasaki, Mamoru   Shimizu, Elena Rasia, and Klaus Dolag