Consequences on some dark energy-candidates from SN 1997ff

Abstract

We examine the status of various dark energy-models in light of the recently observed SN 1997ff at z ≈ 1.7. The modified data still fit a pure cosmological constant Λ or a quintessence with an equation of state similar to that of Λ. The kinematical Λ-models, Λ ∼ S−2 and Λ ∼ H2 , also fit the data reasonably well and require less dark energy density (hence more matter energy density) than is required by the constant Λ-model. However, the model Λ ∼ S−2 with low energy density becomes unphysical as it cannot accommodate higher redshift objects. We also examine an alternative explanation of the data, viz., the absorp- tion by the intervening whisker-like dust and find that the quasi-steady state model and the FRW model Ωm0 = 0.33, without any dark energy also fit the data reasonably well. We notice that the addition of SN 1997ff to the old data has worsened the fit to most of the models, except a closed FRW model with a constant Λ and a closed quintessence-model with ωφ = −0.82, and the models have started departing from each other as we go above z = 1. However, to make a clear discrimination possible, a few more supernovae with z > 1 are required. We have also calculated the age of the universe in these models and find that, in the models with a constant Λ, the expansion age is uncomfortably close to the age of the globular clusters. Quintessence-models show even lower age. The kinematical Λ-models are, however, interesting in this con- nection (especially the model Λ ∼ H2 ), which give remarkably large age of the universe.