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摘要
Context. 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.
Aims. 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.
Methods. 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.
Results. The projected galaxy density distribution shows strong subclustering with two dominant structures: a main central component (A), and a northern component (B), visible both in optical and in X-ray, with two other substructures detected at high significance in the optical. At magnitudes fainter than R = 19, the galaxy distribution shows a clear elongation approximately with the east-west axis extending over 4 h(70)(-1) Mpc, while a nearly perpendicular bridge of galaxies along the north- south axis appears to connect (B) to (A). The (A) component shows a bimodal morphology, and the positions of its two density peaks depend on galaxy luminosity: at magnitudes fainter than R = 19, the axis joining the peaks shows a counterclockwise rotation (from NE/SW to E-W) centered on the position of the X-ray maximum. Our final spectroscopic catalog of 512 objects includes 476 new galaxy redshifts. We have identified 361 galaxies as cluster members; among them, 326 have high precision redshift measurements, which allow us to perform a detailed dynamical analysis of unprecedented accuracy. The cluster mean redshift and velocity dispersion are respectively z = 0.2005 +/- 0.0003 and 1434 +/- 60 km s(-1). We spectroscopically confirm that the northern and western components (A2163-B and A2163-C) belong to the A2163 complex. The velocity distribution shows multi-modality, with an overall bimodal structure peaking at similar to 59 200 km s(-1) and similar to 60 500 km s(-1). A significant velocity gradient (similar to 1250 km s(-1)) is detected along the NE/SW axis of the cluster, which partially explains the detected bimodality. A2163 appears to be exceptionally massive: the cluster virial mass is M(vir) = 3.8 +/- 0.4 x 1015 M(circle dot) h(70)(-1).
Conclusions. Our analysis of the optical data, combined with the available information from X-ray observations and predictions of numerical simulations, supports a scenario in which A2163-A has undergone a recent (t similar to 0.5 Gyr) merger along a NE/SW (or E-W) axis, and A2163-B is connected to the main complex, and is probably infalling on A2163-A.
- 出版日期2008-4
- 单位中国地震局
