Invited Review given at the 18th Texas Symposium held in Chicago, December 1996. To be published by World Scientific Press, eds. A. Olinto, J. Frieman, and D. Schramm.

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MEASURING COSMOLOGICAL PARAMETERS

Wendy L. Freedman

Carnegie Observatories, 813 Santa Barbara St., Pasadena, CA 91101


ABSTRACT. In this review, the status of measurements of the matter density (Omegam), the vacuum energy density or cosmological constant (OmegaLambda), the Hubble constant (H0), and ages of the oldest measured objects (t0) are summarized. Measurements of the statistics of gravitational lenses and strong gravitational lensing are discussed in the context of limits on OmegaLambda. Three separate routes to the Hubble constant are considered: the measurement of time delays in multiply-imaged quasars, the Sunyaev-Zel'dovich effect in clusters, and Cepheid-based extragalactic distances. Globular-cluster ages plus a new age measurement based on radioactive dating of thorium in a metal-poor star are briefly summarized. Limits on the product of H0 t0 are also discussed. Many recent, independent dynamical measurements are yielding a low value for the matter density (Omegam ~ 0.2-0.3). A wide range of Hubble constant measurements appear to be converging in the range of 60-80 km/sec/Mpc. Areas where future improvements are likely to be made soon are highlighted; in particular, measurements of anisotropies in the cosmic microwave background. Particular attention is paid to sources of systematic error and the assumptions that underlie many of the measurement methods.


Table of Contents

INTRODUCTION

Omegam - THE MATTER DENSITY
Galaxies and Clusters: Dynamical Measures & Mass-to-Light Ratios
Dynamics of the Local Group
Cluster Baryon Fraction
Peculiar Velocities: Density and Velocity Comparisons
Galaxy Pairwise Velocities

OmegaLambda AND Omegam LIMITS
Gravitational Lens Statistics
Strong Gravitational Lenses
Omegam and OmegaLambda from Type Ia Supernovae

SUMMARY OF CURRENT Omegam AND OmegaLambda MEASUREMENTS

H0 - THE HUBBLE CONSTANT
"Physical" versus "Astronomical" Methods
Gravitational Lenses
Sunyaev Zel'dovich Effect and X-Ray Measurements
The Cepheid-Calibrated Extragalactic Distance Scale

t0 - AGES OF THE OLDEST STARS
Globular Cluster Ages
Thorium Ages

REMAINING ISSUES FOR MEASURING t0

H0t0

COSMOLOGICAL PARAMETERS FROM COSMIC MICROWAVE BACKGROUND ANISOTROPIES

SUMMARY

REFERENCES

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