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 CDM model (SCDM) with $Ω_0 = 1$, $Λ_0=0$ and $h=0.5$; (2) a low-density flat model (FL03) with $Ω_0=0.3$, $Λ_0=0.7$ and $h=0.75$; (3) an open model (OP03) with $Ω_0=0.3$, $Λ_0=0$ and $h=0.75$; (4) a low-density flat model (FL02) with $Ω_0=0.2$, $Λ_0=0.8$ and $h=1$; (5) an open model (OP02) with $Ω_0=0.2$, $Λ_0=0$ and $h=1$; (6) a low-density flat model (FL01) with $Ω_0=0.1$ and $Λ_0=0.9$; (7) an open model (OP01) with $Ω_0=0.1$ and $Λ_0=0$. We find that the density profiles and morphologies of clusters depend both on $Ω_0$ and on $Λ_0$. For $Λ_0=0$, these properties are a monotonic function of $Ω_0$. Clusters in OP01 have the steepest density profiles, their density contours are the roundest and show the smallest center shifts. The other extreme case is SCDM, where clusters show the least steep density profiles and the most elongated contours. For a given $Ω_0$ ($<1$), clusters in the flat model (i.e. with $Λ_0=1-Ω_0$) have flatter density profiles and less substructures than in the corresponding open model. In particular, our results show that low-density flat models with $Ω_0\sim 0.3$, which are currently considered as a successful alternative to SCDM, can produce a substantial fraction of clusters with substructures. This is in contrast to the conception that this kind of models may have serious problem in this aspect.