Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant

Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant

15 May 1998 | Adam G. Riess, Alexei V. Filippenko, Peter Challis, Alejandro Clocchiatti, Alan Diercks, Peter M. Garnavich, Ron L. Gilliland, Craig J. Hogan, Saurabh Jha, Robert P. Kirshner, B. Leibundgut, M. M. Phillips, David Reiss, Brian P. Schmidt, Robert A. Schommer, R. Chris Smith, J. Spyromilio, Christopher Stubbs, Nicholas B. Suntzeff, John Tonry
This paper presents spectral and photometric observations of 10 type Ia supernovae (SNe Ia) in the redshift range 0.16 ≤ z ≤ 0.62, along with data from previous studies. These observations are used to constrain cosmological parameters such as the Hubble constant ($H_0$), mass density ($\Omega_M$), cosmological constant ($\Omega_\Lambda$), deceleration parameter ($q_0$), and the dynamical age of the Universe ($t_0$). The high-redshift SNe Ia are found to be 10% to 15% farther than expected in a low mass density universe without a cosmological constant. Different light curve fitting methods and prior constraints consistently favor models with a positive cosmological constant ($\Omega_\Lambda > 0$) and a current acceleration of the expansion ($q_0 < 0$). The spectroscopically confirmed SNe Ia are statistically consistent with a positive cosmological constant at the 2.8σ and 3.9σ confidence levels, and with a current acceleration of the expansion at the 3.0σ and 4.0σ confidence levels, respectively. Fixing a minimal mass density ($\Omega_M = 0.2$) results in a weaker detection of a positive cosmological constant at the 3.0σ confidence level. For a flat Universe ($\Omega_M + \Omega_\Lambda = 1$), the spectroscopically confirmed SNe Ia require a positive cosmological constant at the 7σ and 9σ confidence levels. A closed Universe by ordinary matter ($\Omega_M = 1$) is ruled out at the 7σ to 8σ confidence level. The dynamical age of the Universe is estimated to be 14.2 ± 1.5 Gyr, including systematic uncertainties in the current Cepheid distance scale. Systematic effects, including progenitor and metallicity evolution, extinction, sample selection bias, local perturbations in the expansion rate, gravitational lensing, and sample contamination, are evaluated and found to not reconcile the data with a zero cosmological constant and a non-accelerating expansion.This paper presents spectral and photometric observations of 10 type Ia supernovae (SNe Ia) in the redshift range 0.16 ≤ z ≤ 0.62, along with data from previous studies. These observations are used to constrain cosmological parameters such as the Hubble constant ($H_0$), mass density ($\Omega_M$), cosmological constant ($\Omega_\Lambda$), deceleration parameter ($q_0$), and the dynamical age of the Universe ($t_0$). The high-redshift SNe Ia are found to be 10% to 15% farther than expected in a low mass density universe without a cosmological constant. Different light curve fitting methods and prior constraints consistently favor models with a positive cosmological constant ($\Omega_\Lambda > 0$) and a current acceleration of the expansion ($q_0 < 0$). The spectroscopically confirmed SNe Ia are statistically consistent with a positive cosmological constant at the 2.8σ and 3.9σ confidence levels, and with a current acceleration of the expansion at the 3.0σ and 4.0σ confidence levels, respectively. Fixing a minimal mass density ($\Omega_M = 0.2$) results in a weaker detection of a positive cosmological constant at the 3.0σ confidence level. For a flat Universe ($\Omega_M + \Omega_\Lambda = 1$), the spectroscopically confirmed SNe Ia require a positive cosmological constant at the 7σ and 9σ confidence levels. A closed Universe by ordinary matter ($\Omega_M = 1$) is ruled out at the 7σ to 8σ confidence level. The dynamical age of the Universe is estimated to be 14.2 ± 1.5 Gyr, including systematic uncertainties in the current Cepheid distance scale. Systematic effects, including progenitor and metallicity evolution, extinction, sample selection bias, local perturbations in the expansion rate, gravitational lensing, and sample contamination, are evaluated and found to not reconcile the data with a zero cosmological constant and a non-accelerating expansion.
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