Institute for Advanced Study Informal Astrophysics Seminar

Galaxy cluster merger statistics are an important component in understanding the formation of large-scale structure. Recent studies suggest a merger bias, that mergers are more highly clustered than other objects of their mass. Cluster mergers are therefore also potential sources of systematic error in the mass calibration of upcoming cluster surveys. It is difficult to study merger properties and evolution directly because identifying cluster mergers in observations is problematic. I will present results from large N-body simulations that quantify the statistical properties of massive halo mergers, specifically investigating the utility of close halo pairs (more accessible to observation) as proxies for mergers. I will elucidate the relationship between pairs and mergers for a wide range of merger timescales, halo masses, and redshifts (0 < z < 1), and show how redshift space distortions alter the picture. I will also present a calibration of the merger kernel; a relationship between the efficiency of merging and the parent halo mass function (also known as coagulation). I will present our investigation of the environmental dependence of this merger efficiency, and discuss how it arises.