The merger history of clusters and its effect on the X-ray properties of the intracluster medium

We investigate mergers undergone by 20 massive (>3 keV) clusters in a hydrodynamical simulation of the LambdaCDM cosmology with radiative cooling. The clusters show a variety of formation histories which affect their X-ray properties and the scatter of the X-ray scaling relations. For the majority of their lifetimes, clusters grow by accreting low entropy material in small subclumps but occasionally undergo a major merger. We identify several different kinds of major merger including double-peaked mergers in which the global intracluster medium merges first (Lx and Tx increase together) and then the cluster cores merge (Lx increases and Tx decreases). Movement in the Lx-Tx plane is dominated by major mergers, usually parallel to the Lx-Tx relation but sometimes perpendicular to it. However there is no simple relationship between scatter in the Lx-Tx relation and either recent merger activity or cluster formation time. The scatter in the Lx-M and Tx-M relations is reduced if properties are measured within R500 rather than Rvir. Clusters at the point of merging (when the luminosity peaks) tend to be spherical and look relaxed which may lead to biases in high-redshift, flux-limited samples.