Published in 1995 Physics Reports, Vol. 261, Issues 5-6, pp. 271-431


THE DENSITY AND PECULIAR VELOCITY FIELDS OF NEARBY GALAXIES

Michael A. Strauss


School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540

and

Jeffrey A. Willick


Observatories of the Carnegie Institute of Washington, 813 Santa Barbara Street, Pasadena, California 91101-1292


Abstract. We review the quantitative science that can be and has been done with redshift and peculiar velocity surveys of galaxies in the nearby universe. After a brief background setting the cosmological context for this work, the first part of this review focuses on redshift surveys. The practical issues of how redshift surveys are carried out, and how one turns a distribution of galaxies into a smoothed density field, are discussed. Then follows a description of major redshift surveys that have been done, and the local cosmography out to 8,000 km s- 1 that they have mapped. We then discuss in some detail the various quantitative cosmological tests that can be carried out with redshift data. The second half of this review concentrates on peculiar velocity studies, beginning with a thorough review of existing techniques. After discussing the various biases which plague peculiar velocity work, we survey quantitative analyses done with peculiar velocity surveys alone, and finally with the combination of data from both redshift and peculiar velocity surveys. The data presented rule out the standard Cold Dark Matter model, although several variants of Cold Dark Matter with more power on large scales fare better. All the data are consistent with the hypothesis that the initial density field had a Gaussian distribution, although one cannot rule out broad classes of non-Gaussian models. Comparison of the peculiar velocity and density fields constrains the Cosmological Density Parameter. The results here are consistent with a flat universe with mild biasing of the galaxies relative to dark matter, although open universe models are by no means ruled out.


Table of Contents

INTRODUCTION

THEORETICAL BACKGROUND
The Big Bang Model and its Parameters
The Gravitational Instability Paradigm
Power Spectra, Initial Conditions, and Dark Matter
The Correlation Function
The Relation Between the Mass and Galaxy Density Fields
Outstanding Questions

REDSHIFT SURVEYS: SETTING THE QUANTITATIVE GROUNDWORK
The Variety of Redshift Surveys
History of Redshift Surveys
The Measurement of Galaxy Redshifts
Determination of the Luminosity and Selection Functions
Luminosity Functions: Scientific Results
Testing the Hubble Law with Redshift Surveys
The Smoothed Density Field
Filling in the Galactic Plane

REDSHIFT SURVEYS: A COSMOGRAPHICAL TOUR

REDSHIFT SURVEYS: GALAXY CLUSTERING
The Two-Point Correlation Function
Distortions in the Clustering Statistics
Redshift Space Distortions
Non-linear Effects
The Power Spectrum
Higher-Order Statistics
The Density Distribution Function and Counts in Cells
Topology and Related Issues
The Dipole
Spherical Harmonics
Recovering the Real Space Density Field
Clustering of Different Types of Galaxies

PECULIAR VELOCITY FIELDS: TECHNIQUES OF MEASUREMENT AND ANALYSIS
Galaxian Distance Indicator Relations
The Tully-Fisher Relation for Spiral Galaxies
The Faber-Jackson and Dn-sigma Relations for Elliptical Galaxies
Universality of the Distance Indicator Relations
Beyond TF and Dn-sigma: A Look to the Future?
Surface Brightness Fluctuations
BCG L-alpha relation
Possible Methods of Future Peculiar Velocity Work
Statistical Bias and Methods of Peculiar Velocity Analysis
Selection vs. Malmquist Bias - Method I vs. Method II
Bias in a Cluster Sample
Bias in a Field Sample
"Inverse" Distance Indicator Relations
The "Method Matrix" of Peculiar Velocity Analysis
Quantifying Statistical Bias
Forward DIs: Selection Bias
Forward DIs: Malmquist Bias
Distance-Dependent Selection Functions: The "Gould Effect"
Inverse DIs: Selection Bias
Inverse DIs: Malmquist Bias
The Method of Landy and Szalay

STATISTICAL MEASURES OF THE VELOCITY FIELD
A History of Observations of Large-Scale Flow
Early Work
1986-1990: The "Great Attractor"
1990-1994: Very Large-Scale Streaming?
The Lauer-Postman Result
Bulk Flows: A Summary
Homogeneous Peculiar Velocity Catalogs
Velocity Correlation Function
The Cosmic Mach Number
Reconstructing the Three-Dimensional Velocity Field
The Initial Density Distribution Function
Higher-Order Moments of the Velocity Field
Voids in the Reconstructed Density Field
Other Approaches to Reconstructing the Velocity Field

COMPARING THE DENSITY AND VELOCITY FIELDS
Comparison via the Velocity Field
Cluster Infall Models
Unparameterized Velocity Field Models
Method II+
Comparison via the Density Field

DISCUSSION
The Initial Power Spectrum
The Distribution Function of the Initial Fluctuations
The Gravitational Instability Paradigm
The Value of Omega0
The Relative Distribution of Galaxies and Mass
Is the Big Bang Model Right?
The Future

REFERENCES

For a postscript version of the article, click here.

Next