Determining the equation of state of dark energy from angular size of compact radio sources and X-ray gas mass fraction of galaxy clusters

Free access article

Issue		A&A Volume 417, Number 3, April III 2004


Page(s)		833 - 837
Section		Cosmology (including clusters of galaxies)
DOI		http://dx.doi.org/10.1051/0004-6361:20034327

A&A 417, 833-837 (2004)
DOI: 10.1051/0004-6361:20034327

Determining the equation of state of dark energy from angular size of compact radio sources and X-ray gas mass fraction of galaxy clusters

Zong-Hong Zhu^{1, 2}, Masa-Katsu Fujimoto² and Xiang-Tao He¹

¹ Department of Astronomy, Beijing Normal University, Beijing 100875, China
² National Astronomical Observatory, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan
e-mail: fujimoto.masa-katsu@nao.ac.jp

(Received 15 September 2003 / Accepted 16 December 2003)

Abstract
Using recent measurements of angular size of high- z milliarcsecond compact radio sources compiled by Gurvits et al. (1999) and X-ray gas mass fraction of galaxy clusters published by Allen et al. (2002, 2003), we explore their bounds on the equation of state, $\omega_x \equiv p_x/\rho_x$ , of the dark energy, whose existence has been congruously suggested by various cosmological observations. We relax the usual constraint $\omega_x \ge -1$ , and find that combining the two databases yields a nontrivial lower bound on $\omega_x$ . Under the assumption of a flat universe, we obtain a bound $-2.22 < \omega_x < -0.62$ at 95.4% confidence level. The 95.4% confidence bound goes to $-1 \le \omega_x < -0.60$ when the constraint $\omega_x \ge -1$ is imposed.

Key words: cosmology: cosmological parameters -- cosmology: theory -- cosmology: distance scale -- galaxies: active -- radio continuum: galaxies -- X-ray: galaxies: clusters

Offprint request: Zong-Hong Zhu, zong-hong.zhu@nao.ac.jp

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