New Constraints on Ω_M, Ω_Λ, andwfrom an Independent Set of 11 High‐Redshift Supernovae Observed with theHubble Space Telescope

Abstract

We report measurements of M , à , and w from 11 supernovae (SNe) at z ¼ 0:36 0:86 with high-quality light curves measured using WFPC2 on the Hubble Space Telescope (HST). This is an independent set of high-redshift SNe that confirms previous SN evidence for an accelerating universe. The high-quality light curves available from photometry on WFPC2 make it possible for these 11 SNe alone to provide measurements of the cosmological parameters comparable in statistical weight to the previous results. Combined with earlier Supernova Cosmology Project data, the new SNe yield a measurement of the mass density M ¼ 0:25 þ0:07 À0:06 ðstatisticalÞ AE 0:04 (identified systematics), or equivalently, a cosmological constant of à ¼ 0:75 þ0:06 À0:07 ðstatisticalÞ AE 0:04 (identified systematics), under the assumptions of a flat universe and that the dark energy equation-of-state parameter has a constant value w ¼ À1. When the SN results are combined with independent flat-universe measurements of M from cosmic microwave background and galaxy redshift distortion data, they provide a measurement of w ¼ À1:05 þ0:15 À0:20 ðstatisticalÞ AE 0:09 (identified systematic), if w is assumed to be constant in time. In addition to high-precision light-curve measurements, the new data offer greatly improved color measurements of the high-redshift SNe and hence improved host galaxy extinction estimates. These extinction measurements show no anomalous negative E(BÀV ) at high redshift. The precision of the measurements is such that it is possible to perform a host galaxy extinction correction directly for individual SNe without any assumptions or priors on the parent E(BÀV ) distribution. Our cosmological fits using full extinction corrections confirm that dark energy is required with Pð à > 0Þ > 0:99, a result consistent with previous and current SN analyses that rely on the identification of a low-extinction subset or prior assumptions concerning the intrinsic extinction distribution. , and the National Optical Astronomy Observatory. Based in part on observations made with the European Southern Observatory telescopes (ESO programs 60.A-0586 and 265.A-5721). Based in part on observations made with the Canada-France-Hawaii Telescope, operated by the National

Exploring dark energy with SNAP

“…Precise corrections for dust extinction of eleven more supernovae made possible by accurate HST photometry were shown to support the accelerating expansion and provided tighter constraints on the dark energy equation of state [5]. A sample of high-redshift supernovae reaching z ∼ 1.6 has shown that the supernovae follow the transition from deceleration to acceleration expected as the universe goes from matter domination to dark energy domination [16,5,18]. These space-based measurements have significantly bolstered both the case for dark energy and the efficacy of Type Ia Inner and outer contours delimit 68% and 99% confidence, respectively.…”

“…Samples totaling 39 Type Ia supernovae, segregated into early, middle and late host-galaxy morphologies from an HST Snapshot survey, were shown to support an accelerating expansion [20]. Precise corrections for dust extinction of eleven more supernovae made possible by accurate HST photometry were shown to support the accelerating expansion and provided tighter constraints on the dark energy equation of state [5]. A sample of high-redshift supernovae reaching z ∼ 1.6 has shown that the supernovae follow the transition from deceleration to acceleration expected as the universe goes from matter domination to dark energy domination [16,5,18].…”

“…These space-based measurements have significantly bolstered both the case for dark energy and the efficacy of Type Ia Inner and outer contours delimit 68% and 99% confidence, respectively. On the left, the constraints from the Supernova Cosmology Project sample [9][10][11]5] are shown. These include eleven supernovae with very well-measured colors from HST.…”

Simulations of Dark Energy Cosmologies

“…In the following decade, advances in instrumentation and improved host-galaxy extinction estimators have resulted in precise measurements which rule out dust extinction as an alternative to an accelerating expansion (Riess et al, 2004). Recently direct SN searches, for example with the Hubble space telescope (HST) (Knop et al, 2003), have obtained high quality light curves and are able to constrain the cosmological parameters independently of other datasets. Recent supernovae observations of the distance modulus versus redshift (see Appendix A.1) from the Supernova Legacy Survey (SNLS) and the ESSENCE survey (Miknaitis et al, 2007;Wood-Vasey et al, 2007) are shown in Fig.…”

“…In fact, WMAP measurements together with BAO can completely fix Ω k nearly independently of the dark energy equation of state (Komatsu et al, 2010). As CMB measurements are sensitive to the combination Ω m h 2 , a flatness prior together with constraints on h from HST (Knop et al, 2003) are used to break this degeneracy and obtain good constraints on Ω Λ = 1 − (Ω m h 2 )/h 2 .…”