Pointing to the minimum scatter: the generalized scaling relations for galaxy clusters

TL;DR

This paper introduces a generalized scaling law for galaxy clusters to identify the combination of observables that minimizes mass reconstruction scatter, providing new insights into cluster properties and their evolution.

Contribution

It proposes a unified framework for scaling relations that minimizes scatter and reveals a new relation involving luminosity and temperature for galaxy clusters.

Findings

Identifies a locus in slope space minimizing mass scatter.

Derives a new scaling relation M_tot ~ (LT)^(1/2).

Provides formulas for expected redshift evolution in self-similar models.

Abstract

We introduce a generalized scaling law, M_tot = 10^K A^a B^b, to look for the minimum scatter in reconstructing the total mass of hydrodynamically simulated X-ray galaxy clusters, given gas mass M_gas, luminosity L and temperature T. We find a locus in the plane of the logarithmic slopes $a$ and $b$ of the scaling relations where the scatter in mass is minimized. This locus corresponds to b_M = -3/2 a_M +3/2 and b_L = -2 a_L +3/2 for A=M_gas and L, respectively, and B=T. Along these axes, all the known scaling relations can be identified (at different levels of scatter), plus a new one defined as M_tot ~ (LT)^(1/2). Simple formula to evaluate the expected evolution with redshift in the self-similar scenario are provided. In this scenario, no evolution of the scaling relations is predicted for the cases (b_M=0, a_M=1) and (b_L=7/2, a_L=-1), respectively. Once the single quantities are normalized to the average values of the sample under considerations, the normalizations K corresponding to the region with minimum scatter are very close to zero. The combination of these relations allows to reduce the number of free parameters of the fitting function that relates X-ray observables to the total mass and includes the self-similar redshift evolution.