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

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 <sup>5,6

1</sup> 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

Abstract

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 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 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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Contents

• 1. Introduction
• 2. X-ray data
  • 2.1. ROSAT HRI data
  • 2.2. ASCA data
• 3. Spatial analysis of the X-ray emission
  • 3.1. X-ray/optical centering
  • 3.2. Identification of individual sources
  • 3.3. The cluster emission
• 4. Spectral analysis
  • 4.1. ASCA observations
  • 4.2. Total luminosity of the cluster
• 5. Mass analysis
  • 5.1. X-ray mass determination
  • 5.2. Cl0024+17 as a gravitational lens
• 6. Resolving the mass discrepancy?
• 7. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: March 9, 2000
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