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For refcode 1993MNRAS.264...71v:
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Copyright by Royal Astronomical Society. 1993MNRAS.264...71v The dynamics of the outer regions of the Coma cluster Michiel P, van Haarlem, Laura Cayon, Carlos Gutierrez de la Cruz, Enrique Martinez-Gonzalez and Rafael Rebolo Sterrewacht Leiden, PO Box 9513,2300 RA Leiden, The Netherlands Dpto Fisica Moderna, Facultad de Ciencias, Universidad de Cantabria and Instituto de estudios Avanzados en Fisica Moderna y Biologia Molecular, CSIC-Universidad de Cantabria, Avenida Los Castros s/n, 39005 Santander Cantabria, Spain Instituto de Astrofisica de Canarias, La Laguna E-38200, Tenerife, Spain Accepted 1993 February 17. Received 1993 January 11; in original form 1992 September 14 ABSTRACT We apply the spherical infall model to compare the observed distribution of radial velocities of galaxies around Coma with predictions that are based on optical and X-ray overdensity profiles. Two optically selected galaxy catalogues, the CfA redshift survey and a UKST plate scanned with the APM, are used to determine the overdensity profile of the cluster. The two sets of predicted caustics in the angular separation-redshift diagram are compared with a radial velocity catalogue which we have extended significantly in the range between 10 and 40 from the centre of the Coma cluster. In total, we have measured 98 new redshifts. Despite almost doubling the number of radial velocities in this interval, we fail to find the caustics with any degree of certainty. Using recent X-ray-based density profiles of Coma, we derive an independent prediction of the caustics in redshift space. The velocities predicted using these X-ray profiles are in general agreement with the observed velocity distribution. We also investigate the effect that non-spherical mass distributions have on the velocity field in the halo. For a velocity field that is constant on concentric ellipsoids, we show that the caustics are blurred, providing a natural explanation of why we do not see the caustics in Coma. Key words: celestial mechanics, stellar dynamics - galaxies: clusters: individual: Coma - galaxies: distances and redshifts - galaxies: kinematics and dynamics - X-rays: galaxies.
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