Substructures and density profiles of clusters in models of galaxy formation

Abstract

In this paper we investigate, using high-resolution N-body simulations, the density profiles and the morphologies of galaxy clusters in seven models of structure formation. We show that these properties of clusters are closely related to the occurrence of a significant merging event in the recent past. The seven models are: (1) the standard cold dark matter model (SCDM) with Omega_0=1, Lambda_0=0 and h=0.5; (2) a low-density flat model (FL03) with Omega_0=0.3, Lambda_0=0.7 and h=0.75; (3) an open model (OP03) with Omega_0=0.3, Lambda_0=0 and h=0.75; (4) a low-density flat model (FL02) with Omega_0=0.2, Lambda_0=0.8 and h=1; (5) an open model (OP02) with Omega_0=0.2, Lambda_0=0 and h=1; (6) a low-density flat model (FL01) with Omega_0=0.1 and Lambda_0=0.9 and (7) an open model (OP01) with Omega_0=0.1 and Lambda_0=0. We find that the density profiles and morphologies of clusters depend both on Omega_0 and on Lambda_0=0, these properties are a monotonic function of Omega_0. Clusters in OP01 have the steepest density profiles, their density contours are the roundest and show the smallest centre shifts among the density contours. The other extreme case is SCDM, where clusters show the least steep density profiles and the most elongated contours. For a given Omega_0 (<1), clusters in the flat model (i.e. with Lambda_0=1-Omega_0) have flatter density profiles and more substructures than in the corresponding open model. Clusters in FL03 have density profiles and centre shifts close to those in SCDM, although their density contours are rounder. Our results show that, although cluster density profiles and morphologies are useful cosmological tests, low-density flat models with Omega_0~0.3, which are currently considered as a successful alternative to SCDM, can produce a substantial fraction of clusters with substructures. This is in contrast to conclusions drawn from previous work.