Measurements of Ω and Λ from 42 High‐Redshift Supernovae

Abstract

We report measurements of the mass density, Ω M , and cosmological-constant energy density, Ω Λ , 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 fit 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 lightcurve width-luminosity relation. The measurement yields a joint probability distribution of the cosmological parameters that is approximated by the relation 0.8 Ω M − 0.6 Ω Λ ≈ −0.2 ± 0.1 in the region of interest (Ω M ∼ < 1.5). For a flat (Ω M + Ω Λ = 1) cosmology we find Ω flat M = 0.28 +0.09 −0.08 (1σ 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 non-zero 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 t flat 0 = 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 which 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.

Friedman—Robertson—Walker Models with Late-Time Acceleration

“…These models are mainly motivated by the cosmological observations of the supernovae of type Ia [4]- [7]. Dark energy is also supported by other observations, for example, the anisotropy measurements of the cosmic microwave background radiation [8]- [9] and the observations of the baryon acoustic oscillations…”

Astrophysical explosions: from solar flares to cosmic gamma-ray bursts

“…The supernova distance determined in this way is independent of the recession velocity as determined by the redshift of the host galaxy. These two independent pieces of information, applied statistically to a large sample of type Ia supernovae, revealed the remarkable, and deeply challenging, result that the Universe is accelerating, most often interpreted as the effect of a 'dark energy' [48,49]. The supernova results coupled with other techniques (fluctuations in the cosmic microwave background radiation, the spatial distributions of galaxies and the growth of clusters of galaxies) suggest that this effect is consistent with Einstein's cosmological constant in a Universe that is geometrically flat.…”

Modifying gravity: you cannot always get what you want

“…In particular, both the Universe's current expansion and its expansion at some epoch in the very distant past seem to involve acceleration. The current accelerating expansion is inferred by direct observation of the recession velocity (redshift) of distant type 1a supernovae as a function of their distance, as derived from their apparent brightness (originally [12,13]; most recently [14][15][16][17][18][19][20]); these supernovae are standard candles once one recalibrates to account for their different masses.…”