Reconstructing the Three‐dimensional Structure of Underlying Triaxial Dark Halos from X‐Ray and Sunyaev‐Zel’dovich Effect Observations of Galaxy Clusters

Abstract

While the use of galaxy clusters as tools to probe cosmology is established, their conventional description still relies on spherical and/or isothermal models that were proposed more than 20 years ago. We present, instead, a deprojection method for extracting their intrinsic properties from X-ray and Sunyaev-Zel'dovich effect observations in order to improve our understanding of cluster physics. First, we develop a theoretical model for the intracluster gas in hydrostatic equilibrium in a triaxial dark matter halo with a constant axis ratio. In this theoretical model, the gas density profiles are expressed in terms of the intrinsic properties of the dark matter halos. Then, we incorporate the projection effect into the gas profiles and show that the gas surface brightness profiles are expressed in terms of the eccentricities and the orientation angles of the dark halos. For the practical purpose of our theoretical model, we provide several empirical fitting formulae for the gas density and temperature profiles and also for the surface brightness profiles relevant to X-ray and Sunyaev-Zel'dovich effect observations. Finally, we construct a numerical algorithm to determine the halo eccentricities and orientation angles using our model and demonstrate that it is possible in principle to reconstruct the three-dimensional structures of the dark halos from the X-ray and/or Sunyaev-Zel'dovich effect cluster data alone, without requiring priors, such as weak-lensing information, and without relying on such restrictive assumptions as halo axial symmetry about the line of sight.