Generalized Chaplygin gas as a unified scenario of dark matter/energy: Observational constraints

Free access article

Issue		A&A Volume 423, Number 2, August IV 2004


Page(s)		421 - 426
Section		Cosmology (including clusters of galaxies)
DOI		http://dx.doi.org/10.1051/0004-6361:20040236

A&A 423, 421-426 (2004)
DOI: 10.1051/0004-6361:20040236

Generalized Chaplygin gas as a unified scenario of dark matter/energy: Observational constraints

Z.-H. Zhu

Department of Astronomy, Beijing Normal University, Beijing 100875, PR China
e-mail: zong-hong.zhu@nao.ac.jp National Astronomical Observatories, Chinese Academie of Sciences, Beijing 100012, PR China

National Astronomical Observatory, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan

(Received 10 February 2004 / Accepted 30 March 2004)

Abstract
Although various cosmological observations congruously suggest that our universe is dominated by two dark components, the cold dark matter without pressure and the dark energy with negative pressure, the nature and origin of these components is yet unknow. The generalized Chaplygin gas (gCg), parametrized by an equation of state, $p = -A/\rho_{\rm gCg}^{\alpha}$ , was recently proposed to be a candidate of the unified dark matter/energy (UDME) scenarios. In this work, we investigate some observational constraints on it. We mainly focus our attention on the constraints from recent measurements of the X-ray gas mass fractions in clusters of galaxies published by Allen et al. (2002, MNRAS, 334, L11; 2003, 342, 257) and the dimensionless coordinate distances to type Ia supernovae and Fanaroff-Riley type IIb radio galaxies compiled by Daly & Djorgovski (2003, ApJ, 597, 9). We obtain the confidence region on the two parameters fully characterizing gCg, $A_{\rm s} \equiv A/\rho_{{\rm gCg}0}^{(1+\alpha)}$ and $\alpha$ , from a combined analysis of these databases, where $\rho_{{\rm gCg}0}$ is the energy density of gCg at present. It is found that $A_{\rm s}=0.70^{+0.16}_{-0.17}$ and $\alpha=-0.09^{+0.54}_{-0.33}$ , at a 95% confidence level, which is consistent within the errors with the standard dark matter + dark energy model, i.e., the case of $\alpha = 0$ . Particularly, the standard Chaplygin gas ( $\alpha=1$ ) is ruled out as a feasible UDME by the data at a 99% confidence level.

Key words: cosmology: cosmological parameters -- cosmology: theory -- stars: supernovae: general -- galaxies: distances and redshifts -- X-rays: galaxies: clusters

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.