Non-Nucleosynthetic Constraints on the Baryon Density and Other Cosmological Parameters

Details Non-Nucleosynthetic Constraints on the Baryon Density and Other Cosmological Parameters Non-Nucleosynthetic Constraints on the Baryon Density and Other Cosmological Parameters

1997-08-02

arxiv.org/abs/astro-ph/9708016v2

Astrophys.J. 510 (1999) 564-575

Astronomy and Astrophysics

Astrophysics

Version accepted for ApJ. New section with figures showing effect of smaller Gamma; other minor changes. 18 pages including 14

Scientific paper

10.1086/306589

Because the baryon-to-photon ratio eta_{10} is in some doubt, we drop nucleosynthetic constraints on eta_{10} and fit the three cosmological parameters (h, Omega_M, eta_{10}) to four observational constraints: Hubble parameter h_o = 0.70+-0.15, age of the universe t_o = 14+7-2 Gyr, cluster gas fraction f_o \equiv f_G h^{3/2} = 0.060 +- 0.006, and effective shape parameter Gamma_o = 0.255 +- 0.017. Errors quoted are 1 sigma, and we assume Gaussian statistics. We experiment with a fifth constraint Omega_o = 0.2 +- 0.1 from clusters. We set the tilt parameter n = 1 and the gas enhancement factor Upsilon = 0.9. We consider CDM models (open and Omega_M = 1) and flat LambdaCDM models. We test goodness of fit and draw confidence regions by the Delta chi^2 method. CDM models with Omega_M = 1 (SCDM models) are accepted only because the large error on h_o allows h < 0.5. Baryonic matter plays a significant role in Gamma_o when Omega_M \sim 1. Open CDM models are accepted only for Omega_M \gtrsim 0.4. The combination of the four other constraints with Omega_o = 0.2 +- 0.1 is rejected in CDM models with 98% confidence, suggesting that light may not trace mass. LambdaCDM models give similar results. In all of these models, eta_{10} \gtrsim 6 is favored strongly over eta_{10} \lesssim 2. This suggests that reports of low deuterium abundances on QSO lines of sight may be correct and that observational determinations of primordial 4He may have systematic errors. Plausible variations on n and Upsilon in our models do not change the results much. If we drop or change the crucial Gamma_o constraint, lower values of Omega_M and eta_{10} are permitted. The constraint Gamma_o = 0.15 +- 0.04, derived recently from the IRAS redshift survey, favors Omega_M \approx 0.3 and eta_{10} \approx 5 but does not exclude eta_{10} \approx 2.

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