Browsing by Author "Barris, B"

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    Cosmological results from high-z supernovae
    (2003) Tonry, JL; Schmidt, BP; Barris, B; Candia, P; Challis, P; Clocchiatti, A; Coil, AL; Filippenko, AV; Garnavich, P; Hogan, C; Holland, ST; Jha, S; Kirshner, RP; Krisciunas, K; Leibundgut, B; Li, WD; Matheson, T; Phillips, MM; Riess, AG; Schommer, R; Smith, RC; Sollerman, J; Spyromilio, J; Stubbs, CW; Suntzeff, NB
    The High-z Supernova Search Team has discovered and observed eight new supernovae in the redshift interval z = 0.3-1.2. These independent observations, analyzed by similar but distinct methods, confirm the results of Riess and Perlmutter and coworkers that supernova luminosity distances imply an accelerating universe. More importantly, they extend the redshift range of consistently observed Type Ia supernovae (SNeIa) to z approximate to 1, where the signature of cosmological effects has the opposite sign of some plausible systematic effects. Consequently, these measurements not only provide another quantitative confirmation of the importance of dark energy, but also constitute a powerful qualitative test for the cosmological origin of cosmic acceleration. We find a rate for SN Ia of (1.4 +/- 0.5) x 10(-4) h(3) Mpc(-3) yr(-1) at a mean redshift of 0.5. We present distances and host extinctions for 230 SN Ia. These place the following constraints on cosmological quantities: if the equation of state parameter of the dark energy is w = -1, then H(0)t(0) = 0.96 +/- 0.04, and Omega(Lambda) - 1.4Omega(M) = 0.35 +/- 0/14. Including the constraint of a. at universe, we find Omega(M) = 0.28 +/- 0.05, independent of any large-scale structure measurements. Adopting a prior based on the Two Degree Field (2dF) Redshift Survey constraint on Omega(M) and assuming a. at universe, we find that the equation of state parameter of the dark energy lies in the range -1.48 < w < -0.72 at 95% confidence. If we further assume that w > -1, we obtain w < -0.73 at 95% confidence. These constraints are similar in precision and in value to recent results reported using the WMAP satellite, also in combination with the 2dF Redshift Survey.
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    Hubble Space Telescope observations of nine high-redshift essence supernovae
    (2005) Krisciunas, K; Garnavich, PM; Challis, P; Prieto, JL; Riess, AG; Barris, B; Aguilera, C; Becker, AC; Blondin, S; Chornock, R; Clocchiatti, A; Covarrubias, R; Filippenko, AV; Foley, RJ; Hicken, M; Jha, S; Kirshner, RP; Leibundgut, B; Li, WD; Matheson, T; Miceli, A; Miknaitis, G; Rest, A; Salvo, ME; Schmidt, BP; Smith, RC; Sollerman, J; Spyromilio, J; Stubbs, CW; Suntzeff, NB; Tonry, JL; Wood-Vasey, WM
    We present broadband light curves of nine supernovae ranging in redshift from 0.5 to 0.8. The supernovae were discovered as part of the ESSENCE project, and the light curves are a combination of Cerro Tololo 4 m and Hubble Space Telescope (HST) photometry. On the basis of spectra and/or light-curve fitting, eight of these objects are definitely Type Ia supernovae, while the classification of one is problematic. The ESSENCE project is a 5 yr endeavor to discover about 200 high-redshift Type Ia supernovae, with the goal of tightly constraining the time average of the equation-of-state parameter [w = p/(rho c(2))] of the "dark energy." To help minimize our systematic errors, all of our ground-based photometry is obtained with the same telescope and instrument. In 2003 the highest redshift subset of ESSENCE supernovae was selected for detailed study with HST. Here we present the first photometric results of the survey. We find that all but one of the ESSENCE supernovae have slowly declining light curves and that the sample is not representative of the low-redshift set of ESSENCE Type Ia supernovae. This is unlikely to be a sign of evolution in the population. We attribute the decline-rate distribution of HST events to a selection bias at the high-redshift edge of our sample and find that such a bias will infect other magnitude-limited Type Ia supernova searches unless appropriate precautions are taken.