Book contents
- Frontmatter
- Contents
- Preface
- Introduction
- Part I Idealized homogeneous systems – basic ideas and gentle relaxation
- Part II Infinite inhomogeneous systems – galaxy clustering
- 20 How does matter fill the Universe?
- 21 Gravitational instability of the infinite expanding gas
- 22 Gravitational graininess initiates clustering
- 23 Growth of the two-galaxy correlation function
- 24 The energy and early scope of clustering
- 25 Later evolution of cosmic correlation energies
- 26 N-body simulations
- 27 Evolving spatial distributions
- 28 Evolving velocity distributions
- 29 Short review of basic thermodynamics
- 30 Gravity and thermodynamics
- 31 Gravithermodynamic instability
- 32 Thermodynamics and galaxy clustering; ξ(r)∝r-2
- 33 Efficiency of gravitational clustering
- 34 Non-linear theory of high order correlations
- 35 Problems and extensions
- 36 Bibliography
- Part III Finite spherical systems – clusters of galaxies, galactic nuclei, globular clusters
- Part IV Finite flattened systems – galaxies
- Index
28 - Evolving velocity distributions
Published online by Cambridge University Press: 05 July 2011
- Frontmatter
- Contents
- Preface
- Introduction
- Part I Idealized homogeneous systems – basic ideas and gentle relaxation
- Part II Infinite inhomogeneous systems – galaxy clustering
- 20 How does matter fill the Universe?
- 21 Gravitational instability of the infinite expanding gas
- 22 Gravitational graininess initiates clustering
- 23 Growth of the two-galaxy correlation function
- 24 The energy and early scope of clustering
- 25 Later evolution of cosmic correlation energies
- 26 N-body simulations
- 27 Evolving spatial distributions
- 28 Evolving velocity distributions
- 29 Short review of basic thermodynamics
- 30 Gravity and thermodynamics
- 31 Gravithermodynamic instability
- 32 Thermodynamics and galaxy clustering; ξ(r)∝r-2
- 33 Efficiency of gravitational clustering
- 34 Non-linear theory of high order correlations
- 35 Problems and extensions
- 36 Bibliography
- Part III Finite spherical systems – clusters of galaxies, galactic nuclei, globular clusters
- Part IV Finite flattened systems – galaxies
- Index
Summary
Naturally, peculiar velocities must grow consistently with increased spatial clustering. Again, N-body simulations provide valuable insight, especially into the non-linear regime. Since velocity distributions depend strongly on the amount of clustering it is important to separate galaxies according to the density contrast in their local neighborhood.
For the 4000-body experiments, for example, it is possible to use the integration scheme itself to determine the number density inside the nearest neighbor sphere surrounding any galaxy. This sphere is essentially where the fluctuating component dominates the gravitational force. The result is a measure of the local density contrast, which varies from about 104 or 105 in the centers of rich clusters to less than 0.5 in the field galaxies. A subset of field galaxies may be selected by also requiring them to be separated from their nearest neighbor by at least twice the average separation that a uniform random distribution would have. These most isolated galaxies are called extreme field galaxies. They are almost always well outside the haloes of clusters.
As an indication of the relative degree of isolation these criteria imply, at R = 32 (the present time) in the Ω = 0.1, n = -1 model, about 23% of all the galaxies are in clusters (density contrast > 100), about 62% are intermediate (100 > contrast > 0.5), 15% are field galaxies and 5% are extreme field galaxies.
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- Chapter
- Information
- Gravitational Physics of Stellar and Galactic Systems , pp. 195 - 201Publisher: Cambridge University PressPrint publication year: 1985