Published in PASP 1992, 104: 1109-1138

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DARK MATTER IN GALAXIES

Keith M. Ashman


Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218. and Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 1A1.


Abstract. Current ideas on the amount, distribution, and nature of dark matter in galaxies are reviewed. Observations indicate that dark halos surround most, if not all, galaxies. Recent evidence suggests that many dwarf galaxies have higher dark matter fractions than normal galaxies as well as higher central dark matter densities. Some spiral galaxy rotation curves are rising and others are falling at the optical radius, thereby weakening the "disk-halo conspiracy." Observational and theoretical techniques to probe the dark halos of ellipticals are becoming more refined, and various methods are being employed to investigate the shape of halos. There are useful constraints on the extent of the dark matter around our own Galaxy, whereas in some other galaxies the edge of the halo may have been detected. Microlensing experiments have recently commenced which may soon uncover the nature of the Galactic dark matter. These and the other issues reviewed here have far-reaching implications for galaxy formation and evolution, and a variety of cosmological questions.


Table of Contents

INTRODUCTION

THE SOLAR NEIGHBORHOOD

THE MILKY WAY HALO

DWARF SPHEROIDALS
Recent Observational Techniques and Results
Constraining the Dark Matter Distribution
Dispensing with Dark Matter

DWARF IRREGULARS
Observations of Individual Galaxies
Trends in Dark Matter Properties

SPIRAL GALAXIES
Mass Models of Spiral Galaxies
The End of a Conspiracy?
The Dark Matter Fraction in Spirals
The Edge of the Halo
Dust in Spirals

ELLIPTICAL GALAXIES
X-Rays and Globular Clusters
Stellar Velocity Dispersions
Gas Disks

GALAXIES IN PAIRS, GROUPS AND CLUSTERS
Binary Galaxies
Galaxies in Groups
Galaxies in Clusters

THE SHAPE OF DARK HALOS
Polar Ring Galaxies
Warped and Flaring Disks
N-Body Experiments

DARK MATTER SEARCHES AND CONSTRAINTS
Non-Baryonic Dark Matter
Baryonic Dark Matter
Gravitational Lensing

THEORETICAL IMPLICATIONS
Non-Newtonian Gravity
Galaxy Formation and Baryonic Halos
The Hubble Sequence

CONCLUSIONS

REFERENCES

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