Transition Redshift: New Kinematic Constraints from Supernovas

The transition redshift (deceleration/acceleration) is discussed by expanding the deceleration parameter to first order around its present value. A detailed study is carried out by considering two different parameterizations: q = q0 + q1z and q = q0 + q1z(1 + z) , and the associated free parameters (qo, q1) are constrained by 3 different supernova samples. The previous analysis by Riess et al. [ApJ 607, 665, 2004] using the first expansion is slightly improved and confirmed at light of their recent data (Gold07 sample). However, by fitting the model with the Supernova Legacy Survey (SNLS) type Ia sample we find that the best fit to the redshift transition is zt = 0.61 instead of zt = 0.46 as derived by the High-z Supernovae Search (HZSNS) team. This result based in the SNLS sample is also in good agreement with the Davies et al. sample, zt = 0.60 +0.28 −0.11 (1σ). Such results are in line with some independent analyzes and accommodates more easily the concordance flat model (ΛCDM). For both parameterizations, the three SNe type Ia samples considered favor recent acceleration and past deceleration with a high degree of statistical confidence level. All the kinematic results presented here depend neither on the validity of general relativity nor the matter-energy contents of the Universe. Subject headings: cosmology, luminosity distance, dark energy, SNe Ia