The origin of scatter in the X-ray luminosity - halo mass relation of galaxy clusters

TL;DR

This study investigates the sources of scatter in the X-ray luminosity-halo mass relation of galaxy clusters using large hydrodynamical simulations, identifying key properties that reduce scatter and providing formulas for practical use.

Contribution

It introduces the first comprehensive analysis of factors influencing scatter in the X-ray luminosity-halo mass relation, including new correlations with ICM and SZ properties, validated across different simulation models.

Findings

Gas fraction and SZ signal strongly correlate with X-ray scatter.

Accounting for these properties reduces scatter by over 50%.

Correlations vary with feedback strength and redshift.

Abstract

Galaxy groups and clusters are excellent probes of large-scale structure and are shaped by some of the most energetic physical processes in the Universe. They follow a tight scaling relation of X-ray luminosity with halo mass. However, predicting the dependence of the scatter in this relation on mass and redshift is challenging, due to the statistical requirement of large simulation volumes. Using the large volume cosmological hydrodynamical simulations for galaxy cluster physics FLAMINGO and TNG300+TNG-Cluster, we fit this relation and its scatter, focusing on $M_{\rm 500c}>10^{13}~\mathrm{M_\odot}$ and $z \leq 2$. We find qualitatively similar, but quantitatively different results for the two models. For the first time, we study ways to reduce the scatter using properties beyond X-ray luminosity, namely six ICM, six galaxy, and eleven dark matter halo properties. For both FLAMINGO and TNG300+TNG-Cluster, the gas fraction and thermal Sunyaev-Zel'dovich (SZ) signal correlate strongest with X-ray scatter, reducing it by over 50% when accounting for their partial correlations. Galaxy and halo properties correlate weakly with X-ray scatter, typically reducing it by 10-20%. Our results are qualitatively robust across different FLAMINGO feedback variations, though the correlations weaken for stronger feedback and with increasing redshift. Differences between FLAMINGO and TNG300+TNG-Cluster are only apparent at the high-mass end - where e.g. the galaxy stellar age correlates strongly for FLAMINGO, but not for TNG300+TNG-Cluster - confirming robustness across physics implementations. We provide fitting formulas for the scatter and its corrections, for direct application to cosmological analyses and observational data.