We consider a sample of about 50 distant galaxy clusters at z > 0.15 (< z >∼ 0.3), each cluster having at least 10 galaxies with available redshift in the literature. We select member galaxies, analyze the velocity dispersion profiles, and evaluate in a homogeneous way cluster velocity dispersions and virial masses. We apply the same procedures already recently applied on a sample of nearby clu...

By using the ENACS data, we have studied the properties of emission-line galaxies (ELG) in clusters. The fraction of ELG in clusters is 16 %; this fraction is slightly dependent on the cluster velocity dispersion, being larger for \colder" systems. ELG tend to occur more frequently than other cluster galaxies in substructures. However, only a minor cluster fraction has an ELG population with a ...

We have studied the poor southern cluster of galaxies S639. Based on new Strömgren photometry of stars in the direction of the cluster we confirm that the galactic extinction affecting the cluster is large. We find the extinction in Johnson B to be AB = 0.75± 0.03. We have obtained new photometry in Gunn r for E and S0 galaxies in the cluster. If the Fundamental Plane is used for determination ...

We investigate the kinetics of generic single-species reaction processes when the reactants move ballistically, namely ballistic annihilation, A + A 0, and a ballistic aggregation process which mimics traffic flow on a single-lane roadway. For ballistic annihilation, dimensional analysis shows that the concentration and root means square velocity decay as c P and u N r-6, respectively, with a +...

We present high resolution N-body/SPH simulations of the interacting cluster 1E0657−56. The main and the sub-cluster are modeled using extended cuspy ΛCDM dark matter halos and isothermal β-profiles for the collisional component. The hot gas is initially in hydrostatic equilibrium inside the global potential of the clusters. We investigate the X-ray morphology and derive the most likely impact ...

Aims. We obtained VLT/FLAMES+UVES high-resolution, fibre-fed spectroscopy of five young massive clusters (YMCs) in M83 (NGC 5236). This forms the basis of a pilot study testing the feasibility of using fibre-fed spectroscopy to measure the velocity dispersions of several clusters simultaneously, in order to determine their dynamical masses. In principle, this reduces the telescope time required...

Redshifts of several galaxies thought to be associated with NGC 326 are determined. The results confirm the presence of a cluster and find a mean redshift of z = 0.0477 ± 0.0007 and a line-of-sight velocity dispersion σ z = 599 (+230, −110) km s −1. The velocity dispersion and previously measured X-ray gas temperature of kT ≃ 1.9 keV are consistent with the cluster σ z /kT relation, and NGC 326...

We have carried out additional spectroscopic observations in the field of cluster Cl 1324+3011 at z = 0.76. Combined with the spectroscopy presented in Postman, Lubin & Oke (2001, AJ, 122, 1125), we now have spectroscopically confirmed 47 cluster members. With this significant number of redshifts, we measure accurately the cluster velocity dispersion to be 1016 −93 km s −1. The distribution of ...

We investigate the star-formation properties of dynamically relaxed galaxy clusters as a function of cluster mass for 308 low-redshift clusters drawn from the Sloan Digital Sky Survey (SDSS) C4 cluster catalog. It is important to establish if cluster star-formation properties have a mass dependence before comparing clusters at different epochs, and here we use cluster velocity dispersion, σ, as...