Large-scale structure and motions from simulated galaxy clusters.pdf

a s t r o - p h / 9 3 1 0 0 1 6 1 1 O c t 9 3 Large-scale structure and motions from simulatedgalaxy clusters.R. A. C. Croft and G. Efstathiou AbstractWe use high resolution dissipationless N-body simulations to examine the spatial dis-tribution of galaxy clusters on large scales. The Standard CDM model and two of itsmain competitors, Low density CDM and Mixed Dark Matter are compared. The two-point correlation function of simulated clusters is compared with an extended surveyof APM clusters , and it is found that Standard CDM exhibits a lack of power on allscales, whereas the two alternative scenarios are able to match the spatial correlationswell. Of the remaining two models, the velocities in the MDM universe have a higheramplitude and their distribution is much broader . We compare these peculiar velocitieswith observations and nd that both models have diculty in reproducing the observednumbers of very high peculiar velocity clusters. The reliable detection of several moreclusters with velocities in excess of 1000km s1 would render the LCDM scenario inparticular very unlikely.1. IntroductionClusters of galaxies eciently trace out the large scale structure of the universe. Mea-surements of their spatial correlation function in and 2 and 3 dimensions[11;3;13] providedsome of the rst evidence that there is more power in the clustering of matter than can beaccounted for by the standard CDM model. More recently, surveys of rich clusters pickedfrom computer generated galaxy catalogues[7;17] , and a survey of ROSAT X-ray clusters[18]indicate that their 3D two-point correlation function has the following form:cc(r)  (r=r0)1:8 r0  13 16 h1Mpc (1)(the Hubble constant is H0 = 100hkm s1 Mpc1). We have run a series of N-bodysimulations to determine whether equation (1) can be reproduced by the standard CDMmodel, or by variants such as Low density CDM or Mixed Dark Matter. The simulations,described in Section 2.1 , are large enough to resolve individual cl