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Astron. Astrophys. 338, 813-818 (1998)

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Updating the [FORMULA]-T relationship for galaxy clusters *

Xiang-Ping Wu 1, Li-Zhi Fang 2 and Wen Xu 2

1 Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing 100012, P.R. China
2 Department of Physics, University of Arizona, Tucson, AZ 85721, USA

Received 15 October 1997 / Accepted 12 August 1998


The relationship between the X-ray determined temperature T of the intracluster gas and the optical measured velocity dispersion [FORMULA] of the cluster galaxies is often believed to be not only a straightforward but also robust test for the dynamical properties of galaxy clusters. Here, we present the [FORMULA]-T relationship using the 94 clusters drawn from the largest sample of 149 clusters in literature, for which both [FORMULA] and T are observationally determined. Employment of the doubly weighted orthogonal distance regression to our sample yields [FORMULA], indicating an apparent deviation of dynamical state from that predicted by the isothermal and hydrostatic equilibrium model for galaxy clusters, though the average ratio [FORMULA] of specific energy in galaxies to that in gas is found to be in excellent agreement with unity. It shows that a nonisothermal gas distribution with a mean polytropic index of [FORMULA] can account for the reported [FORMULA]-T relationship, while overall clusters can still be regarded as dynamically-relaxed systems.

Key words: galaxies: clusters: general – X-rays: galaxies

* Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr ( or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?JA+A/338/813

Send offprint requests to: X.P. Wu

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© European Southern Observatory (ESO) 1998

Online publication: September 17, 1998