Joint estimation of cosmological parameters from cosmic microwave background and IRAS data

Observations of large-scale structure (LSS) and of the cosmic microwave bac kground (CMB) each place separate constraints on the values of cosmological parameters. We calculate a joint likelihood based on various CMB experimen ts and the IRAS 1.2 Jy galaxy redshift survey and use this to find an overa ll optimum with respect to the free parameters. Our formulation self-consis tently takes account of the underlying mass distribution, which affects bot h the CMB potential fluctuations and the IRAS redshift distortion. This not only allows more accurate parameter estimation but also removes the parame ter degeneracy that handicaps calculations based on either approach alone. The family of cold dark matter models analyzed corresponds to a spatially f lat universe with an initially scale-invariant spectrum and a cosmological constant. Free parameters in the joint model are the mass density due to al l matter (Omega(m)), Hubble's parameter (h = H-o/100 km s(-1) Mpc(-1)), the quadrupole normalization of the CMB power spectrum (Q) in mu K, and the IR AS light-to-mass bias (b(IRAS)). Throughout the analysis, the baryonic dens ity (Omega(b)) is required to satisfy the nucleosynthesis constraint Omega( b)h(2) = 0.024. Results from the two data sets show good agreement, and the joint optimum lies at Omega(m) = 0.39, h = 0.53, Q = 16.95 mu K, and b(IRA S) = 1.21. The 68% confidence intervals are 0.29 < Omega(m) < 0.53, 0.39 < h < 0.58, 15.34 < Q < 17.60, and 0.98 < b(IRAS) < 1.56. For the above param eters, the normalization and shape of the mass power spectrum are sigma(8) = 0.67 and Gamma = 0.15, and the age of the universe is 16.5 Gyr.