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ApJ 517 (1999 June 1) 565-586   doi: 10.1086/307221

Measurements of Ω and Λ from 42 High-Redshift Supernovae


S. Perlmutter1,12, G. Aldering1, G. Goldhaber1,12, R. A. Knop1, P. Nugent1, P. G. Castro1,13, S. Deustua1, S. Fabbro1,14, A. Goobar1,15, D. E. Groom1, I. M. Hook1,16, A. G. Kim1,12,17, M. Y. Kim1, J. C. Lee1,18, N. J. Nunes1,13, R. Pain1,14, C. R. Pennypacker1,19, R. Quimby1, C. Lidman2, R. S. Ellis3, M. Irwin3, R. G. McMahon3, P. Ruiz-Lapuente4, N. Walton5, B. Schaefer6, B. J. Boyle7, A. V. Filippenko8, T. Matheson8, A. S. Fruchter9, N. Panagia9,20, H. J. M. Newberg10, W. J. Couch11 and The Supernova Cosmology Project
1 Institute for Nuclear and Particle Astrophysics, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA 94720
2 European Southern Observatory, La Silla, Chile
3 Institute of Astronomy, Cambridge, England, UK
4 Department of Astronomy, University of Barcelona, Barcelona, Spain
5 Isaac Newton Group, La Palma, Spain
6 Department of Astronomy, Yale University, New Haven, CT
7 Anglo-Australian Observatory, Sydney, Australia
8 Department of Astronomy, University of California, Berkeley, CA
9 Space Telescope Science Institute, Baltimore, MD
10 Fermi National Laboratory, Batavia, IL
11 University of New South Wales, Sydney, Australia
12 Center for Particle Astrophysics, University of California, Berkeley, California
13 Instituto Superior Técnico, Lisbon, Portugal
14 LPNHE, CNRS-IN2P3, and University of Paris VI and VII, Paris, France
15 Department of Physics, University of Stockholm, Stockholm, Sweden
16 European Southern Observatory, Munich, Germany
17 PCC, CNRS-IN2P3, and Collège de France, Paris, France
18 Institute of Astronomy, Cambridge, England, UK
19 Space Sciences Laboratory, University of California, Berkeley, California
20 Space Sciences Department, European Space Agency

ABSTRACT. We report measurements of the mass density, ΩM, and cosmological-constant energy density, ΩΛ, of the universe based on the analysis of 42 type Ia supernovae discovered by the Supernova Cosmology Project. The magnitude-redshift data for these supernovae, at redshifts between 0.18 and 0.83, are fitted jointly with a set of supernovae from the Calán/Tololo Supernova Survey, at redshifts below 0.1, to yield values for the cosmological parameters. All supernova peak magnitudes are standardized using a SN Ia light-curve width-luminosity relation. The measurement yields a joint probability distribution of the cosmological parameters that is approximated by the relation 0.8ΩM-0.6ΩΛapprox-0.2±0.1 in the region of interest (ΩMlesssim1.5). For a flat (ΩM+ΩΛ=1) cosmology we find ΩMflat=0.28+0.09-0.08 (1 σ statistical) +0.05-0.04 (identified systematics). The data are strongly inconsistent with a Λ=0 flat cosmology, the simplest inflationary universe model. An open, Λ=0 cosmology also does not fit the data well: the data indicate that the cosmological constant is nonzero and positive, with a confidence of P(Λ>0)=99%, including the identified systematic uncertainties. The best-fit age of the universe relative to the Hubble time is t0flat=14.9+1.4-1.1(0.63/h) Gyr for a flat cosmology. The size of our sample allows us to perform a variety of statistical tests to check for possible systematic errors and biases. We find no significant differences in either the host reddening distribution or Malmquist bias between the low-redshift Calán/Tololo sample and our high-redshift sample. Excluding those few supernovae that are outliers in color excess or fit residual does not significantly change the results. The conclusions are also robust whether or not a width-luminosity relation is used to standardize the supernova peak magnitudes. We discuss and constrain, where possible, hypothetical alternatives to a cosmological constant.

Subject headings: cosmology: observations; distance scale; supernovae: general

Print publication: Issue 2 (1999 June 1)
Received 8 September 1998, accepted for publication 17 December 1998

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