Dark Energy and Hubble Constant From the Latest SNe Ia, BAO and SGL

Based on the latest MLCS17 SNe Ia data provided by Hicken et al. (2009), together with the Baryon Acoustic Oscillation (BAO) and strong gravitational lenses (SGL), we investigate the dark energy equation-of-state parameter for both constant w and time-varying w(z) = w0 + waz/(1 + z) in the flat universe, and its correlation with the matter density ΩM and Hubble constant h. The constraints from SNe data alone arrive at: (a) the best-fit results are (ΩM , w, h) = (0.358,−1.09, 0.647), while both ΩM and w are very sensitive to the difference ∆h = h− h̃ of the Hubble constant deviating to the prior input h̃ = 0.65; (b) the likelihoods of parameters are found to be: w = −0.88 −0.39 and ΩM = 0.36 −0.15, which is consistent with the ΛCDM at 95% C.L.; (c) the two parameters in the time-varying case are found to be (w0, wa) = (−0.73 −0.97, 0.84 −10.34) after marginalizing other parameters; (d) there is a clear degeneracy between constant w and ΩM , which depresses the power of SNe Ia to constrain both of them; (e) the likelihood of parameter wa has a high non-Gaussian distribution; (f) an extra restriction on ΩM is necessary to improve the constraint of the SNe Ia data on (w0, wa). A joint analysis of SNe Ia data and BAO is made to break the degeneracy between w and ΩM , and it provides a stringent constrain with the likelihoods: w = −0.88 −0.09 and ΩM = 0.29 −0.03. For the time-varying w(z), it leads to the interesting maximum likelihoods w0 = −0.94 and wa = 0. When marginalizing the parameters ΩM and h, the fitting results are found to be (w0, wa) = (−0.95 −0.18, 0.41 −0.96). After adding the splitting angle statistic of SGL data, a consistent constraint is obtained (ΩM , w) = (0.298,−0.907) and (w0, wa) is further improved to be (w0, wa) = (−0.92 −0.10, 0.35 −0.54), which indicates that the phantom type models are disfavored.