Browsing by Author "Holland, ST"

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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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    The optical afterglow of the gamma-ray burst GRB 012111
    (2002) Holland, ST; Soszynski, I; Gladders, MD; Barrientos, LF; Berlind, P; Bersier, D; Garnavich, PM; Jha, S; Stanek, KZ
    We present early-time optical photometry and spectroscopy of the optical afterglow of the gamma-ray burst GRB 011211. The spectrum of the optical afterglow contains several narrow metal lines that are consistent with the burst's occurring at a redshift of 2.14 +/- 0.001. The optical afterglow decays as a power law with a slope of alpha = 0.83 +/- 0.04 for the first approximate to2 days after the burst, at which time there is evidence of a break. The slope after the break is greater than or equal to 1.4. There is evidence of rapid variations in the R-band light approximately 0.5 days after the burst. These variations suggest that there are density fluctuations near the gamma-ray burst on spatial scales of approximately 40-125 AU. The magnitude of the break in the light curve, the spectral slope, and the rate of decay in the optical suggest that the burst expanded into an ambient medium that is homogeneous on large scales. We estimate that the local particle density is between approximately 0.1 and 10 cm(-3) and that the total gamma-ray energy in the burst was (1.2-1.9) x 10(50) ergs. This energy is smaller than, but consistent with, the "standard" value of (5 +/- 2) x 10(50) ergs. Comparing the observed color of the optical afterglow with predictions of the standard beaming model suggests that the rest-frame V-band extinction in the host galaxy is less than or similar to0.03 mag.
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    Twenty-three high-redshift supernovae from the Institute for Astronomy Deep Survey
    (2004) Barris, BJ; Tonry, JL; Blondin, S; Challis, P; Chornock, R; Clocchiatti, A; Filippenko, AV; Garnavich, P; Holland, ST; Jha, S; Kirshner, RP; Krisciunas, K; Leibundgut, B; Li, WD; Matheson, T; Miknaitis, G; Riess, AG; Schmidt, BP; Smith, RC; Sollerman, J; Spyromilio, J; Stubbs, CW; Suntzeff, NB; Aussel, H; Chambers, KC; Connelley, MS; Donovan, D; Henry, JP; Kaiser, N; Liu, MC; Martín, EL; Wainscoat, RJ
    We present photometric and spectroscopic observations of 23 high-redshift supernovae (SNe) spanning a range of z = 0.34-1.03, nine of which are unambiguously classified as Type Ia. These SNe were discovered during the IfA Deep Survey, which began in 2001 September and observed a total of 2.5 deg(2) to a depth of approximately m approximate to 25-26 in RIZ over 9-17 visits, typically every 1-3 weeks for nearly 5 months, with additional observations continuing until 2002 April. We give a brief description of the survey motivations, observational strategy, and reduction process. This sample of 23 high-redshift SNe includes 15 at z greater than or equal to 0.7, doubling the published number of objects at these redshifts, and indicates that the evidence for acceleration of the universe is not due to a systematic effect proportional to redshift. In combination with the recent compilation of Tonry et al. (2003), we calculate cosmological parameter density contours that are consistent with the flat universe indicated by the cosmic microwave background (Spergel et al. 2003). Adopting the constraint that Omega(total) = 1.0, we obtain best-fit values of (Omega(m), Omega(Lambda)) = (0.33, 0.67) using 22 SNe from this survey augmented by the literature compilation. We show that using the empty-beam model for gravitational lensing does not eliminate the need for Omega(Lambda) > 0. Experience from this survey indicates great potential for similar large-scale surveys while also revealing the limitations of performing surveys for z > 1 SNe from the ground.