Astronomy and Astrophysics – Astrophysics
Scientific paper
1995-09-28
Astrophys.J. 460 (1996) 10
Astronomy and Astrophysics
Astrophysics
17 pages, uuencoded, compressed Postscript file, to appear in Astrophysical Journal
Scientific paper
10.1086/176948
The observed baryon fraction and velocity--temperature relation in clusters of galaxies are compared with hydrodynamic simulations in two cosmological models : standard (Omega = 1) and a low-density flat (Omega=0.45 and \lambda=0.55) CDM models, normalized to the COBE background fluctuations. The observed properties of clusters include the velocity dispersion versus temperature relation, the gas mass versus total mass relation, and the gas mass fraction versus velocity dispersion relation. We find that, while both cosmological models reproduce well the shape of these observed functions, only low-density CDM can reproduce the observed amplitudes. The cluster gas mass fraction reflects approximately the baryon fraction in the models, with a slight anti-bias. Therefore, due to the low baryon density given by nucleosynthesis, Omega = 1 models produce too few baryons in clusters compared with observations. Scaling our results as a function of Omega, we find that a low-density CDM model, with Omega approximately 0.3 - 0.4, best reproduces the observed mean baryon fraction in clusters. The observed beta parameter of clusters, beta = sigma^2/(k T/mu m_p) = 0.94 \pm 0.08 discriminates less well between the models; it is consistent with that produced by low-density CDM (1.10 \pm 0.22), while it is slightly larger than expected but still consistent with Omega = 1 (0.70 \pm 0.14).
Bahcall Neta A.
Cen Renyue
Lubin Lori Maxine
Ostriker Jeremiah P.
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