A2163 is among the richest and most distant Abell clusters, presenting outstanding properties in different wavelength domains. X-ray observations have revealed a distorted gas morphology and strong features have been detected in the temperature map, suggesting that merging processes are important in this cluster. However, the merging scenario is not yet well-defined. We have undertaken a complementary optical analysis, aiming to understand the dynamics of the system, to constrain the merging scenario and to test its effect on the properties of galaxies. We present a detailed optical analysis of A2163 based on new multicolor wide-field imaging and medium-to-high resolution spectroscopy of several hundred galaxies.
We present a detailed dynamical analysis of the rich galaxy cluster A2744, containing a powerful diffuse radio-halo. Our analysis is based on redshift data for 102 galaxies, part of them recovered from unexplored spectra in the ESO archive. We combine galaxy velocity and position information to select the cluster members and determine global dynamical properties of the cluster. We use a variety of statistical tests to detect possible substructures. We find that A2744 appears as a well isolated peak in the redshift space at <z>=0.306, which includes 85 galaxies recognized as cluster members. We compute the line-of-sight (LOS) velocity dispersion of galaxies, sigma_V_=1767_-99_^121^km/s, which is significantly larger than what is expected in the case of a relaxed cluster with an observed X-ray temperature of 8 keV. We find evidence that this cluster is far from dynamical equilibrium, as shown by the non Gaussianity of the velocity distribution, the presence of a velocity gradient and a significant substructure. Our analysis shows the presence of two galaxy-clumps of different mean LOS velocities DeltaV~4000km/s. We detect a main, low-velocity clump with sigma_V_~1200-1300km/s and a secondary, high-velocity clump with sigma_V_=500-800km/s and located in the S-SW cluster region. We estimate a cluster mass within 1Mpc of 1.4-2.4M_{sun}_, depending on the model adopted to describe the cluster dynamics. Our results suggest a merging scenario of two clumps with a mass ratio of 3:1 and a LOS impact velocity of DeltaV_rf_~3000km/s, likely observed just after the core passage. The merging is occuring roughly in the NS direction with the axis close to the LOS. This scenario agrees with that proposed on the basis of recent Chandra results in its general lines although pointing out for a somewhat more advanced merging phase. Our conclusions support the view of the connection between extended radio emission and energetic merging phenomena in galaxy clusters.
We report 102 new redshifts and magnitudes for a sample of galaxies to R_F_~15.5mag in a 2.17{deg}x2.17{deg} region centered on the galaxy IC 4296, the most luminous member of the A3565 Cluster. The sample of galaxies was defined from scans of an on-film copy of the ESO/Uppsala survey field 383 in the R band (IIIa-F emulsion plus GG 630 filter; hereafter ESO-LV) using the Observatsrio Nacional PDS 1010A microdensitometer.
We have obtained 65 new redshifts in 4 Abell galaxy as well as 15 velocities of galaxies observed through the galactic plane, at ESO and OHP. Data on individual galaxies are presented, and the accuracy of the determined velocities are discussed as well as some properties of the clusters.
As a part of our galaxy-cluster redshift survey, we present a set of 79 new velocities in the 4 clusters Abell 376, Abell 970, Abell 1356, and Abell 2244, obtained at Haute-Provence observatory. This set now completes our previous analyses, especially for the first two clusters. Data on individual galaxies are presented, and we discuss some cluster properties.
A detailed dynamical analysis of the nearby rich Norma cluster (ACO 3627) is presented. From radial velocities of 296 cluster members, we find a mean velocity of 4871+/-54km/s and a velocity dispersion of 925km/s. The mean velocity of the E/S0 population (4979+/-85km/s) is offset with respect to that of the S/Irr population (4812+/-70km/s) by {Delta}v=164km/s in the cluster rest frame. This offset increases towards the core of the cluster. The E/S0 population is free of any detectable substructure and appears relaxed. Its shape is clearly elongated with a position angle that is aligned along the dominant large-scale structures in this region, the so-called Norma wall. The central cD galaxy has a very large peculiar velocity of 561km/s which is most probably related to an ongoing merger at the core of the cluster.
We present a new insight on NGC 6034 and UGC 842, two groups of galaxies previously reported in the literature as being fossil groups. The study is based on optical photometry and spectroscopy obtained with the CTIO Blanco telescope and Sloan Digital Sky Survey archival data.
We present the results of a new spectroscopic and photometric survey of the hot, binary X-ray cluster A115 at z=0.193, containing a radio relic. Our analysis is based on new spectroscopic data obtained at the Telescopio Nazionale Galileo for 115 galaxies and on new photometric data obtained at the Isaac Newton Telescope in a large field. We combine galaxy velocity and position information to select 85 galaxies recognized as cluster members, determine global dynamical properties and detect substructures.
We present the results of the dynamical analysis of the rich, hot, and X-ray very luminous galaxy cluster A2219, containing a powerful diffuse radio-halo. Our analysis is based on new redshift data for 27 galaxies in the cluster region, measured from spectra obtained at the Telescopio Nazionale Galileo (TNG), with the addition of other 105 galaxies recovered from reduction of CFHT archive data in a cluster region of about 5-arcmin radius (about 0.8Mpc/h at the cluster distance) centered on the cD galaxy. The investigation of the dynamical status is also performed by using X-ray data stored in the Chandra archive. Further, valuable information comes from other bands - optical photometric, infrared, and radio data - which are analyzed and/or discussed, too. Our analyses support the view of the connection between extended radio emission and merging phenomena in galaxy clusters.
We present 546 optical redshifts obtained for galaxies in the region of the Horologium-Reticulum supercluster (HRS) using the 6{deg} field (6dF) multifiber spectrograph on the UK Schmidt Telescope at the Anglo-Australian Observatory. The HRS covers an area of more than 12{deg}x12{deg} on the sky centered at approximately RA=03h19m, DE=-50{deg}02'.
