The impact of mergers on relaxed X-ray clusters – II. Effects on global X-ray and Sunyaev–Zel'dovich properties and their scaling relations

We use the suite of simulations presented by Poole et al. to examine global X-ray and Sunyaev–Zel'dovich (SZ) observables for systems of merging relaxed X-ray clusters. The time evolution of our merging systems' X-ray luminosities, temperatures, total mass measures, SZ central Compton parameters and integrated SZ fluxes are presented and the resulting impact on their scaling relations examined. In all cases, and for all parameters, we observe a common time evolution: two rapid transient increases during first and second pericentric passage, with interceding values near or below their initial levels. This is in good qualitative agreement with previous idealized merger simulations, although we find several important differences related to the inclusion of radiative cooling in our simulations. These trends translate into a generic evolution in the scaling-relation planes as well: a rapid transient roughly along the mass scaling relations, a subsequent slow drift across the scatter until virialization, followed by a slow evolution along and up the mass scaling relations as cooling recovers in the cluster cores. However, this drift is not sufficient to account for the observed scatter in the scaling relations. We also study the effects of mergers on several theoretical temperature measures of the intracluster medium: emission-weighted measures (Tew), the spectroscopic-like measure (Tsl) proposed by Mazzotta et al. and plasma model fits to the integrated spectrum of the system (Tspec). We find that Tsl tracks Tspec for the entire duration of our mergers, illustrating that it remains a good tool for observational comparison even for highly disturbed systems. Furthermore, the transient temperature increases produced during first and second pericentric passage are 15–40 per cent larger for Tew than for Tsl or Tspec. This suggests that the effects of transient temperature increases on σ8 and ΩM derived by Randall et al. are over estimated. Lastly, we examine the X-ray SZ proxy proposed by Kravtsov, Vikhlinin & Nagai (2006) and find that the tight mass scaling relation they predict remains secure through the entire duration of a merger event, independent of projection effects.