Nature versus Nurture: The curved spine of the galaxy cluster X-ray luminosity -- temperature relation

TL;DR

This study uses hydrodynamical simulations to explore how galaxy cluster mergers influence the X-ray luminosity-temperature relation, revealing that mergers cause clusters to move along and below the relation, with brightest clusters often being recent merger remnants.

Contribution

It provides new insights into the physical processes shaping the L-T relation, emphasizing the role of mergers in cluster evolution and luminosity variations.

Findings

Mergers boost clusters along and below the L-T relation.

Brightest clusters are typically near the peak of a merger.

Clusters at the top of the L-T relation formed earlier.

Abstract

The physical processes that define the spine of the galaxy cluster X-ray luminosity -- temperature (L-T) relation are investigated using a large hydrodynamical simulation of the Universe. This simulation models the same volume and phases as the Millennium Simulation and has a linear extent of 500 h^{-1} Mpc. We demonstrate that mergers typically boost a cluster along but also slightly below the L-T relation. Due to this boost we expect that all of the very brightest clusters will be near the peak of a merger. Objects from near the top of the L-T relation tend to have assembled much of their mass earlier than an average halo of similar final mass. Conversely, objects from the bottom of the relation are often experiencing an ongoing or recent merger.