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Astron. Astrophys. 355, 433-442 (2000)

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X-ray observations and mass determinations in the cluster of galaxies Cl0024+17 *

G. Soucail 1, N. Ota 2, H. Böhringer 3, O. Czoske 1, M. Hattori 4 and Y. Mellier 5,6

1 Observatoire Midi-Pyrénées, Laboratoire d'Astrophysique, UMR 5572, 14 Avenue E. Belin, 31400 Toulouse, France
2 Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan
3 Max-Planck-Institut für Extraterrestrische Physik, Gießenbachstrasse, 85740 Garching bei München, Germany
4 Astronomical Institute, Tôhoku University, Aoba Aramaki, Sendai 980, Japan
5 Institut d'Astrophysique de Paris, 98 bis Boulevard Arago, 75014 Paris, France
6 Observatoire de Paris, DEMIRM, 61 Avenue de l'Observatoire, 75014 Paris, France

Received 4 November 1999 / Accepted 17 January 2000


We present a detailed analysis of the mass distribution in the rich and distant cluster of galaxies Cl0024+17. X-ray data come from both a deep ROSAT HRI image of the field (B"ohringer et al., 2000) and ASCA spectral data. Using a wide field CCD image of the cluster, we optically identify all the faint X-ray sources, whose counts are compatible with deep X-ray number counts. In addition we marginally detect the X-ray counter-part of the gravitational shear perturbation detected by Bonnet et al. (1994) at a 2.5 [FORMULA] level. A careful spectral analysis of ASCA data is also presented. In particular, we extract a low resolution spectrum of the cluster free from the contamination by a nearby point source located 1.2 arcmin from the center. The X-ray temperature deduced from this analysis is [FORMULA] keV at the 90% confidence level. The comparison between the mass derived from a standard X-ray analysis and from other methods such as the Virial Theorem or the gravitational lensing effect lead to a mass discrepancy of a factor 1.5 to 3. We discuss all the possible sources of uncertainties in each method of mass determination and give some indications on the way to reduce them. A complementary study of optical data is in progress and may solve the X-ray/optical discrepancy through a better understanding of the dynamics of the cluster.

Key words: galaxies: clusters: general – galaxies: clusters: individual: Cl0024+17 – cosmology: observations – cosmology: dark matter – cosmology: gravitational lensing – X-rays: galaxies

* Based on observations with the ROSAT and ASCA satellites and with the Canada-France-Hawaii Telescope at Mauna Kea, Hawaii, USA

Send offprint requests to: G. Soucail (soucail@obs-mip.fr)

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© European Southern Observatory (ESO) 2000

Online publication: March 9, 2000