A parametric physical model for the intracluster medium and its use in joint SZ/X-ray analyses of galaxy clusters

TL;DR

This paper introduces a parametric model for the intra-cluster medium that combines SZ and X-ray data analysis, accurately estimating cluster properties and highlighting limitations of traditional models.

Contribution

The paper develops and tests a new entropy-based model for galaxy clusters that improves joint SZ/X-ray analysis accuracy over traditional methods.

Findings

Accurately reproduces cluster temperature, mass, and gas fraction.

Performs well outside the core region (r > kpc).

Single isothermal beta model can cause significant biases.

Abstract

We present a parameterized model of the intra-cluster medium that is suitable for jointly analysing pointed observations of the Sunyaev-Zel'dovich (SZ) effect and X-ray emission in galaxy clusters. The model is based on assumptions of hydrostatic equilibrium, the Navarro, Frenk and White (NFW) model for the dark matter, and a softened power law profile for the gas entropy. We test this entropy-based model against high and low signal-to-noise mock observations of a relaxed and recently-merged cluster from N-body/hydrodynamic simulations, using Bayesian hyper-parameters to optimise the relative statistical weighting of the mock SZ and X-ray data. We find that it accurately reproduces both the global values of the cluster temperature, total mass and gas mass fraction (fgas), as well as the radial dependencies of these quantities outside of the core (r > kpc). For reference we also provide a comparison with results from the single isothermal beta model. We confirm previous results that the single isothermal beta model can result in significant biases in derived cluster properties.