Context. In nearby clusters early-type galaxies follow isotropic orbits. The orbits of late-type galaxies are instead characterized by slightly radial anisotropy. Little is known about the orbits of the different populations of cluster galaxies at redshift z > 0.3. Aims. We investigate the redshift evolution of the orbits of cluster galaxies. Methods. We use two samples of galaxy clusters spann...

We present cross sections and reaction rates for merging to occur during encounters of equal-mass spherical galaxies. As an application, we determine the rate of galaxy merging in clusters of galaxies. We present results for two types of Plummer models (a full and a truncated one), two King models and the Hernquist model. Cross sections are determined on the basis of a large number (∼ 500) of s...

We propose a new approach to unveil the presence of binary intermediate mass black holes (IMBHs) in the core of globular clusters (GCs). We study the signature that a binary IMBH imprints on the velocity and on the angular momentum of cluster stars, simulating 3-body encounters between a star and a binary IMBH. We find that the binary IMBH generates a family of few hundreds of stars (∼ 100-300)...

We study the rms peculiar velocity of clusters as a convenient statistic to put constraints on cosmological models. This statistic is easy to compute theoretically given a model for the power spectrum; we show that with some assumptions it can be directly related to the quantity Ω 0 σ8. We develop a likelihood method for estimating the rms peculiar velocity of clusters from line-of-sight veloci...

We report an analysis of the dynamical structure of clusters of galaxies from a survey of photometric and spectroscopic observations in the fields of southern Abell Clusters. We analyze the galaxy velocity field in extended regions up to 7h Mpc from cluster centers and we estimate mean velocity dispersions and their radial dependence. Only one from a total number of 41 Abell clusters does not c...

Galaxy cluster mass distribution are potentially useful probes of Ω0 and the nature of the dark matter. Large clusters will distort the observed shapes of background galaxies through gravitational lensing allowing the measurement of the cluster mass distributions. In this paper we describe weak statistical lensing measurements of the most luminous X-ray cluster known, RXJ1347.5-1145 at z = 0.45...

The distributions of peculiar velocities of rich clusters and of groups of galaxies are investigated for different cosmological models and are compared with observations. Four cosmological models are studied: standard (Ω = 1) CDM, low-density CDM, HDM (Ω = 1), and PBI. We find that rich clusters of galaxies exhibit a Maxwellian distribution of peculiar velocities in all models, as expected from...

We consider here the collective accretion of gas by globular clusters and dwarf galaxies moving through the interstellar medium. In the limit of high velocity and/or sound speed of the ISM, the collective potential of the cluster is insufficient to accrete significant amounts of gas, and stars within the systems accrete gas individually. We show, however, that when the sound speed or the relati...

We propose a new approach to study the dynamical implications of mass models of clusters for the velocity structure of galaxies in the core. Strong and weak lensing data are used to construct the total mass profile of the cluster, which is used in conjunction with the optical galaxy data to solve in detail for the nature of galaxy orbits and the velocity anisotropy in the central regions. We al...

If binaries are common among massive stars, it will have important consequences for the derivation of fundamental properties like the cluster age, IMF and dynamical mass. Making use of the multiplexing facilities of Gemini Multi Object Spectrograph (GMOS) we were able to investigate the presence of binary stars within the ionising cluster of 30 Doradus. From a seven epochs observing campaign at...