F. Durret

Weak lensing and spectroscopic analysis of the nearby dissociative merging galaxy cluster Abell 3376

The galaxy cluster Abell~3376 is a nearby (z=0.046) dissociative merging cluster surrounded by two prominent radio relics and showing an X-ray comet-like morphology. The merger system is comprised of the subclusters A3376W & A3376E. Based on new deep multi-wavelength large-field images and published redshifts, we bring new insights about the history of this merger. Despite the difficulty of applying the weak lensing technique at such low redshift, we successfully recovered the mass distribution in the cluster field. Moreover, with the application of a two-body model, we have addressed the dynamics of these merging system. We have found the individual masses of M_{200}^{W}=3.0_{-1.7}^{+1.3}x10^{14} M_{odot} and M_{200}^{E}=0.9_{-0.8}^{+0.5}x10^{14} M_{odot}. The cometary shaped X-ray distribution shows only one peak spatially coincident with both Eastern BCG and the A3376E mass peak whereas the gas content of A3376W seems to be stripped out. Our data allowed us to confirm the existence of a third subcluster located at the North, 1147+-62 kpc apart from the neighbour subcluster A3376E and having a mass M_{200}^{N}=1.4_{-1.0}^{+0.7}x10^{14} M_{odot}. From our dynamical analysis, we found the merging is taking place very close to the plane of the sky, with the merger axis just 10 deg +-11 deg from it. The application of a two-body analysis code showed that the merging cluster is seen 0.9_{-0.3}^{+0.2} Gyr after the pericentric passage and it is currently going to the point of maximum separation between the subclusters.

Redshift and Photometric Survey of the X-ray Cluster of Galaxies Abell 85

We obtained a catalogue of 4232 galaxies in the rich cD cluster of galaxies A 85 (z=0.0556) by scanning a bJ Schmidt plate with the MAMA measuring machine in a region of ±1° ; magnitudes were recalibrated with six CCD fields in V and R. We also obtained 421 redshifts, which added to the 150 in the literature[2,6] gave a catalogue of 551 galaxies.

Two Physical Laws for Elliptical Galaxies: Photometrical Consequences

We show from theoretical calculations that elliptical galaxies obey two laws: 1) Their specific entropy is quasi-constant and 2) A scaling relation exists between potential energy and mass.

Substructure in ABCG 2256: Wavelet Analysis of ROSAT Image

The image of the cluster of galaxies ABCG 2256 obtained by ROSAT (and retrieved from the data bank) shows the presence of structures on different scales (Figure 1).