Discovery of a new fundamental plane dictating galaxy cluster evolution from gravitational lensing

TL;DR

This study uncovers a fundamental plane relating galaxy cluster properties, revealing how their thermodynamic history and growth through accretion shape their structure, supported by observational data and simulations.

Contribution

It identifies a new fundamental plane in galaxy clusters linking radius, mass, and temperature, explained by a similarity solution and confirmed by simulations.

Findings

Galaxy clusters lie on a tight fundamental plane in parameter space.

The plane's tilt is explained by continuous accretion and growth.

Numerical simulations reproduce the observed plane and its angle.

Abstract

In cold dark matter (CDM) cosmology, objects in the Universe have grown under the effect of gravity of dark matter. The intracluster gas in a galaxy cluster was heated when the dark-matter halo formed through gravitational collapse. The potential energy of the gas was converted to thermal energy through this process. However, this process and the thermodynamic history of the gas have not been clearly characterized in connection with with the formation and evolution of the internal structure of dark-matter halos. Here, we show that observational CLASH data of high-mass galaxy clusters lie on a plane in the three-dimensional logarithmic space of their characteristic radius $r_s$, mass $M_s$, and X-ray temperature $T_X$ with a very small orthogonal scatter. The tight correlation indicates that the gas temperature was determined at a specific cluster formation time, which is encoded in $r_s$ and $M_s$. The plane is tilted with respect to $T_X \propto M_s/r_s$, which is the plane expected in case of simplified virial equilibrium. We show that this tilt can be explained by a similarity solution, which indicates that clusters are not isolated but continuously growing through matter accretion from their outer environments. Numerical simulations reproduce the observed plane and its angle. This result holds independently of the gas physics implemented in the code, revealing the fundamental origin of this plane.