Radial Profile and Lognormal Fluctuations of the Intracluster Medium as the Origin of Systematic Bias in Spectroscopic Temperature

Abstract

The origin of the recently reported systematic bias in the spectroscopictemperature of galaxy clusters is investigated using a cosmologicalhydrodynamic simulation. We find that the local inhomogeneities ofthe gas temperature and density, after being corrected for theirglobal radial profiles, have a nearly universal distribution thatresembles a lognormal function. Based on this lognormal approximationfor the fluctuations in the intracluster medium, we develop an analyticalmodel that explains the bias in the spectroscopic temperature. Weconclude that the multiphase nature of the intracluster medium, duenot only to the radial profiles but also to the local inhomogeneities,plays an essential role in producing the systematic bias.