Published in "The Extragalactic Distance Scale", Space Telescope Science Institute Symposium Series 10, 1997, eds. M. Livio, M. Donahue and N. Panagia


GRAVITATIONAL LENSING AND THE EXTRAGALACTIC DISTANCE SCALE

Roger D. Blandford and Tomislav Kundic


Theoretical Astrophysics, California Institute of Technology, MC 130-33, Pasadena, CA 91125


Abstract. The potential of gravitational lenses for providing direct, physical measurements of the Hubble constant, free from systematic errors associated with the traditional distance ladder, has long been recognized. However, it is only recently that there has been a convincing measurement of a time delay sufficiently accurate to carry out this program. By itself, an accurate time delay measurement does not produce an equivalently definite Hubble constant and the errors associated with models of the primary lens, propagation through the potential fluctuations produced by the large-scale structure and the global geometry of the universe must also be taken into account. The prospects for measuring several more time delays and the feasibility of making the corresponding estimates of the Hubble constant with total error smaller than ten percent are critically assessed.


Table of Contents

INTRODUCTION

THE METHOD

MEASURING TIME DELAYS

Modeling strong galaxy lenses
The models
Modeling "quad" sources
Uncertainties in the models
The double quasar 0957+561

SYSTEMATIC ERRORS

IS A TEN PERCENT MEASUREMENT OF H0 ATTAINABLE?

REFERENCES

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