Vol. 644
3. Cosmology

From universal profiles to universal scaling laws in X-ray galaxy clusters

The properties of galaxy clusters are shaped mainly by gravity and astrophysical dissipative processes and show remarkable universal behavior once they are rescaled by halo mass and redshift. In this work, the authors show that a universal pressure profile of the intracluster medium (ICM) combined with a halo–mass concentration–redshift relation and the hydrostatic equilibrium equations allow for the reconstruction of the radial profiles of the thermodynamical quantities. When they are integrated over a characteristic scale (such as the commonly used R500 radius), as was done in the observations, they produce the most important physical quantities for characterizing clusters, that is to say, the total mass, gas mass, temperature, and so on. These quantities in turn satisfy universal scaling laws. Using a large sample of clusters from the Planck observations, which have homogeneous X-ray data, the authors calibrate the predicted scaling laws. Their model not only reproduces the observed scaling laws well, but it also provides a way to interpret possible deviations from this self-similar behavior of galaxy clusters. For example, this comparison allows for the quantification of the effect of gas clumping on the studied sample.