Browsing by Author "Henry, JP"

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    Cosmological constraints from the evolution of the cluster baryon mass function at z ∼ 0.5
    (2003) Vikhlinin, A; Voevodkin, A; Mullis, CR; VanSpeybroeck, L; Quintana, H; McNamara, BR; Gioia, I; Hornstrup, A; Henry, JP; Forman, WR; Jones, C
    We present a new method for deriving cosmological constraints based on the evolution of the baryon mass function of galaxy clusters and implement it using 17 distant clusters from our 160 deg(2) ROSAT survey. The method uses the cluster baryon mass as a proxy for the total mass, thereby avoiding the large uncertainties of the M-tot-T or M-tot-L-X relations used in all previous studies. Instead, we rely on a well-founded assumption that the M-b/M-tot ratio is a universal quantity, which should result in a much smaller systematic uncertainty. Taking advantage of direct and accurate Chandra measurements of the gas masses for distant clusters, we find strong evolution of the baryon mass function between z > 0.4 and the present. The observed evolution defines a narrow band in the Omega(m)-Lambda plane, Omega(m) + 0.23Lambda = 0.41 +/- 0.10 at 68% confidence, which intersects with constraints from the cosmic microwave background and Type Ia supernovae near Omega(m) = 0.3 and Lambda = 0.7.
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    The 160 Square Degree ROSAT Survey
    (2003) Mullis, CR; McNamara, BR; Quintana, H; Vikhlinin, A; Henry, JP; Gioia, IM; Hornstrup, A; Forman, W; Jones, C
    We present the revised catalog of galaxy clusters detected as extended X-ray sources in the 160 Square Degree ROSAT Survey, including spectroscopic redshifts and X-ray luminosities for 200 of the 201 members. The median redshift is z(median) = 0.25, and the median X-ray luminosity is L-X,L-median = 4.2 x 10(43) h(50)(-2) s(-1) (0.5 - 2.0 keV). This is the largest high-redshift sample of X-ray - selected clusters published to date. There are 73 objects at z > 0.3 and 22 objects at z > 0.5 drawn from a statistically complete flux-limited survey with a median object flux of 1.4 x 10(-13) ergs cm(-2) s(-1). We describe the optical follow-up of these clusters with an emphasis on our spectroscopy, which has yielded 155 cluster redshifts, 110 of which are presented here for the first time. These measurements, combined with 45 from the literature and other sources, provide near-complete spectroscopic coverage for our survey. We discuss the final optical identifications for the extended X-ray sources in the survey region and compare our results to similar X-ray cluster searches.
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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.