Flux-averaging Analysis of Type Ia Supernova Data

We have combined the type Ia supernova (SNe Ia) data from the High-z SN Search and the Supernova Cosmology Project, and binned the combined data by flux-averaging in redshift intervals of ∆z = 0.05 and ∆z = 0.1. We find that the unbinned data yield a Hubble constant of H0 = 65 ± 1 km s−1 Mpc−1 (statistical error only), a matter density fraction of Ωm = 0.7 ± 0.4, and a vacuum energy density fraction of ΩΛ = 1.2± 0.5. The binned data for ∆z = 0.1 yield H0 = 65 ± 1 km s−1 Mpc−1 (statistical error only), Ωm = 0.3 ± 0.6, and ΩΛ = 0.7 ± 0.7. Our results are not sensitive to the redshift bin size. Flux-averaging leads to less biased estimates of the cosmological parameters. Comparison of the data of 18 SNe Ia published by both groups yields a mean SN Ia peak absolute magnitude of MB = −19.33 ± 0.25. If the SNe Ia peak absolute luminosity changes with redshift due to evolution, our ability to measure the cosmological parameters from SNe Ia data will be significantly diminished. Assuming power-law evolution in the peak absolute luminosity, (1 + z) , we find a strong degeneracy between the evolution power-law index β and the matter density fraction Ωm. For Ωm = 0.3, we find that the unbinned data yields H0 = 65 ± 1 km s−1 Mpc−1 (statistical error only), ΩΛ = 1.4 ± 1.1, and β = 0.5 ± 1.6, and the binned data (with ∆z = 0.1) yields H0 = 65 ± 1 km s−1 Mpc−1 (statistical error only), ΩΛ = 0.6 ± 1.4, and β = 0.0± 1.0.