EDP Sciences
Free Access
Volume 402, Number 1, April IV 2003
Page(s) 53 - 63
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361:20030197
Published online 07 April 2003

A&A 402, 53-63 (2003)
DOI: 10.1051/0004-6361:20030197

Observational constraints on general relativistic energy conditions, cosmic matter density and dark energy from X-ray clusters of galaxies and type-Ia supernovae

P. Schuecker1, R. R. Caldwell2, H. Böhringer1, C. A. Collins3, L. Guzzo4 and N. N. Weinberg5

1  Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße 1, 85740 Garching, Germany
2  Department of Physics & Astronomy, Dartmouth College, Hanover, NH 03755, USA
3  Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD, UK
4  INAF-Osservatorio di Brera, via Bianchi, 22055 Merate (LC), Italy
5  California Institute of Technology, Mail Code 130-33, Pasadena, CA 91125, USA

(Received 22 November 2002 / Accepted 6 February 2003)

New observational constraints on the cosmic matter density  $\Omega_{\rm m}$ and an effectively redshift-independent equation of state parameter $w_{\rm x}$ of the dark energy are obtained while simultaneously testing the strong and null energy conditions of general relativity on macroscopic scales. The combination of REFLEX X-ray cluster and type-Ia supernova data shows that for a flat Universe the strong energy condition might presently be violated whereas the null energy condition seems to be fulfilled. This provides another observational argument for the present accelerated cosmic expansion and the absence of exotic physical phenomena related to a broken null energy condition. The marginalization of the likelihood distributions is performed in a manner to include a large fraction of the recently discussed possible systematic errors involved in the application of X-ray clusters as cosmological probes. This yields for a flat Universe, $\Omega_{\rm m}=0.29^{+0.08}_{-0.12}$ and $w_{\rm x}=-0.95^{+0.30}_{-0.35}$ ( $1\sigma$ errors without cosmic variance). The scatter in the different analyses indicates a quite robust result around $w_{\rm x}=-1$, leaving little room for the introduction of new energy components described by quintessence-like models or phantom energy. The most natural interpretation of the data is a positive cosmological constant with $w_{\rm x}=-1$ or something like it.

Key words: cosmology: cosmological parameters -- X rays: galaxies: clusters

Offprint request: P. Schuecker, peters@mpe.mpg.de

© ESO 2003

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