Formation of spiral and elliptical galaxies

Journal Article · Mon Mar 15 00:00:00 EST 1976 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/154214· OSTI ID:7285754

Gott, III, J R; Thuan, T X

The key factor distinguishing an elliptical from a spiral galaxy is proposed to be the amount of gas left over at the point of maximum collapse of the protogalaxy. The gas left depends on the ratio of the star formation time scale tau/sub s/ to the collapse time of the protogalaxy tau/sub c/. Observed properties of ellipticals imply that they formed out of relatively larger density perturbations at recombination, giving them a relatively small tau/sub s//tau/sub c/ (if a rho/sup 2/ star formation law is adopted); and thus they are expected to essentially complete their star formation by the time of maximum collapse. Observations of spiral galaxies and our Galaxy imply that they formed out of less dense density perturbations giving them a larger tau/sub s//tau/sub c/. In the latter, star formation is not nearly completed by the time of maximum collapse. A detailed numerical model including both stars and gas was used to follow the collapse of a spiral galaxy. The gas and stars collapse together until they hit the plane, whereupon the gas forms a disk and the stars relax to form a spheroidal halo. The competing effects of dissipation and turbulent viscosity are analyzed using a model of cloud formation in the early protogalaxy. The gas disk does not hit the plane at its equilibrium position, and both radial and nonaxisymmetric oscillations of the disk are expected before equilibrium is reached. ''Zeroth'' order Maclaurin spheroid models for equilibrium spiral and elliptical galaxies are presented, which relate many useful galactic parameters to the original size and angular momentum. Monte Carlo calculations suggest that the tidal interaction picture of Peebles is capable of explaining the angular momentum of our Galaxy and the observed distribution of ellipticities in elliptical galaxies. This also explains why ellipticals are found preferentially in large clusters: because protogalaxies arising from larger initial density fluctuations cluster more easily. (AIP)

• Research Organization: California Institute of Technology, Pasadena
• OSTI ID: 7285754
• Journal Information: Astrophys. J.; (United States), Vol. 204:3
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
GALACTIC EVOLUTION
COSMIC GASES
GRAVITATIONAL COLLAPSE
ANGULAR MOMENTUM
ELLIPTICAL CONFIGURATION
MECHANICS
SPATIAL DISTRIBUTION
SPIRAL CONFIGURATION
STAR EVOLUTION
TURBULENCE
VISCOSITY
CONFIGURATION
DISTRIBUTION
FLUIDS
GASES
640105* - Astrophysics & Cosmology- Galaxies