Comparison of Supernovae Datasets Constraints on Dark Energy

Cosmological measurements suggest that our universe contains a dark energy component. In order to study the dark energy evolution, we constrain a parameterized dark energy equation of state w(z)=w₀ + w₁ z/1+z using the recent observational datasets: 157 Gold type Ia supernovae and the newly released 182 Gold type Ia supernovae by the maximum likelihood method. It is found that the best fit w(z) crosses -1 in the past and the present best fit value of w(0)<-1 obtained from 157 Gold-type Ia supernovae. The crossing of -1 is not realized and w₀=-1 is not ruled out in 1σ confidence level for the 182 Gold-type Ia supernovae. It is also found that the range of parameter w₀ is wide even in 1σ confidence level and the best fit w(z) is sensitive to the prior of Ωm.