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Astron. Astrophys. 363, 440-450 (2000)

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6. Conclusions and future prospects

The rich cluster Abell 2104 at a redshift of [FORMULA] was found to have a high X-ray luminosity ([FORMULA] ergs s-1 in [0.1-2.4] keV) and temperature ([FORMULA] keV) from ROSAT HRI and ASCA data. The central cooling time, [FORMULA] yr for this cluster indicates the absence of a cooling flow. The galaxy velocity distribution showed that the cD galaxy was at rest at the bottom of the cluster potential. The X-ray image shows significant substructure in the centre of the cluster and an overall elliptical appearance. It appears that the cluster has not yet reached dynamical equilibrium.

As shown in Evrard et al. (1996) and Schindler (1996), the total mass deduced from assumptions of dynamical equilibrium are not significantly different from the true values. The total mass deduced from the X-ray data assuming hydrostatic equilibrium is consistent with the dynamic mass deduced from Jean's equation. However, the current data on the projected galaxy density distribution and our knowledge of the galaxy orbits are limited for studies of cluster dynamics, which allows a wide range of possible parametric functions for the spatial galaxy density distribution without even attempting the non-parametric methods of Merritt & Tremblay (1994) or considering any anisotropic orbits. This can be improved by a deep wide-field observation, to extend the galaxy number density distribution to a large radius (up to 3 Mpc) and to allow a direct measure of the cluster mass from a weak shear analysis. This would allow us to definitively address the issue of whether or not the cluster is in dynamical equilibrium and constrain the range of possible total mass distributions allowed by the wide-range of data from lensing effects to X-rays. In order not to bias the results and incorporate a wide-range of the possible total mass density distributions, a non-parametric method should also be employed. With the launch of XMM and Chandra, we will soon able to obtain a temperature profile and probe the X-ray emission at the edge of the cluster which is crucial to the improvement of the X-ray mass estimates.

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© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000