Measurements of Omega and Lambda from HighRedshift Supernovae
Abstract
We report measurements of the mass density, Omega_M , and cosmologicalconstant energy density, Omega_ Lambda , of the universe based on the analysis of more than forty Type Ia supernovae discovered by the Supernova Cosmology Project. The magnituderedshift data for these high redshift supernovae are fit jointly with a set of supernovae from the Calan/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 lightcurve widthluminosity relation. The measurement yields a joint probability distribution of the cosmological parameters that is approximated by the relation 0.8 Omega_M  0.6 Omega_ Lambda ~ 0.2 +/ 0.1 in the region of interest (Omega_M ≲ 1.5). For a flat (zero curvature) cosmology we find Omega_M = 0.28(+0.09}_{0.08) (statistical) (+0.05}_{0.04) (systematic). The data are strongly inconsistent with a Lambda = 0 zerocurvature cosmology, the simplest inflationary universe model. An open, Lambda = 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(Lambda > 0) = 99%, including the systematic uncertainty. The bestfit age of the universe relative to the Hubble time is t_0=14.9(+1.4}_{1.1) (0.63/h) Gyr for a zerocurvature universe. 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 lowredshift Calan/Tololo sample and our highredshift sample. Excluding those few supernovae which are outliers in color excess or fit residual does not significantly change the results. The conclusions are also robust whether or not a widthluminosity relation is used to standardize the supernova peak magnitudes.
 Publication:

American Astronomical Society Meeting Abstracts
 Pub Date:
 December 1998
 Bibcode:
 1998AAS...193.3904A