Type Ia supernova discoveries at z > 1 from the Hubble Space Telescope: Evidence for past deceleration and constraints on dark energy evolution

TLDR: For a flat universe with a cosmological constant, the transition between the two epochs is constrained to be at z = 0.46 ± 0.13 as mentioned in this paper, and w = -1.02 ± (and w < -0.76 at the 95% confidence level) for an assumed static equation of state of dark energy.

Abstract: We have discovered 16 Type Ia supernovae (SNe Ia) with the Hubble Space Telescope (HST) and have used them to provide the first conclusive evidence for cosmic deceleration that preceded the current epoch of cosmic acceleration. These objects, discovered during the course of the GOODS ACS Treasury program, include 6 of the 7 highest redshift SNe Ia known, all at z > 1.25, and populate the Hubble diagram in unexplored territory. The luminosity distances to these objects and to 170 previously reported SNe Ia have been determined using empirical relations between light-curve shape and luminosity. A purely kinematic interpretation of the SN Ia sample provides evidence at the greater than 99% confidence level for a transition from deceleration to acceleration or, similarly, strong evidence for a cosmic jerk. Using a simple model of the expansion history, the transition between the two epochs is constrained to be at z = 0.46 ± 0.13. The data are consistent with the cosmic concordance model of ΩM ≈ 0.3, ΩΛ ≈ 0.7 (χ = 1.06) and are inconsistent with a simple model of evolution or dust as an alternative to dark energy. For a flat universe with a cosmological constant, we measure ΩM = 0.29 ± (equivalently, ΩΛ = 0.71). When combined with external flat-universe constraints, including the cosmic microwave background and large-scale structure, we find w = -1.02 ± (and w < -0.76 at the 95% confidence level) for an assumed static equation of state of dark energy, P = wρc2. Joint constraints on both the recent equation of state of dark energy, w0, and its time evolution, dw/dz, are a factor of ~8 more precise than the first estimates and twice as precise as those without the SNe Ia discovered with HST. Our constraints are consistent with the static nature of and value of w expected for a cosmological constant (i.e., w0 = -1.0, dw/dz = 0) and are inconsistent with very rapid evolution of dark energy. We address consequences of evolving dark energy for the fate of the universe.

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TABLE 2 SN Ia Imaging

Fig. 8.—Joint confidence intervals for ( M , ) from SNe Ia. The solid contours are results from the gold sample of 157 SNe Ia presented here. The dotted contours are the results from Riess et al. (1998) illustrating the earlier evidence for > 0. Regions representing specific cosmological scenarios are illustrated. Contours are closed by their intersection with the line M ¼ 0.

Fig. 16.—Predicted lensing magnifications of SNe Ia and of random positions in the CDF-S and HDF-N. For the SNe Ia discovered in the GOODS fields, the expected magnification was calculated using a multiple-lens plane formalism, with estimates of foreground lens redshifts and masses derived from the GOODS catalog. Expected magnifications were also calculated for 100 randomly selected positions (redshift and angular position). The solid and dotted lines show redshift bin averages and dispersion, respectively. SNe Ia found in the GOODS survey and in other HST searches are indicated.

Fig. 15.—Comparison of individual distance differences estimated by the MLCS2k2 and BATM methods for the HST and ground-discovered SNe Ia. The zero points of both methods are normalized by using the same set of SNe Ia.

Fig. 2.—Multicolor light curves of SNe Ia. For each SN Ia, multicolor photometry transferred to rest-frame passbands is plotted. The individual, best-fit MLCS2k2 model is shown as a solid line, with a 1 model uncertainty, derived from the model covariance matrix, above and below the best fit.

Fig. 17.—Correlation of the predicted magnification and the best-fit cosmological model residual for individual SNe Ia. The predicted magnifications are as described in Fig. 16. The residuals are the difference in distance modulus as predicted from the best-fit model ( M ¼ 0:3, ¼ 0:7) and as observed. The empirical correlation is expected to be unity (if the lens light traces their mass) and is shown for the whole sample and without SN 1997ff, the SN with the largest residual and predicted magnification.