Dissipation in Galaxy Formation

Astronomy 626: Spring 1995

Cooling Times and Galactic Scales

Only those systems with t_cool < t_dyn can become galaxies before being incorporated into larger structures.

Core Condensation in Heavy Halos

Clustering of dark matter provides potential wells in which luminous galaxies form. The latter survive the merging of their halos because dissipation has increased their binding energies.

Rotation of Disk Galaxies

Torques between objects impart a modest amount of angular momentum. A self-gravitating cloud must then collapse by a large factor to reach centrifugal equilibrium, while the collapse factors for clouds in heavy halos are more reasonable.

Problems

• The cooling catastrophe: rapid cooling in small halos could turn all gas into stars before large galaxies can form.
• In hierarchical pictures, the brighter objects are typically younger, and we would expect them to be bluer as well.
• The predicted luminosity function has too many faint galaxies.

References

• Binney, J. 1977, Ap.J. 215, 483.
• Fall, S.M. & Efstathiou, G.P.E. 1980, M.N.R.A.S. 193, 189.
• Rees, M.J. & Ostriker, J.P. 1977, M.N.R.A.S. 179, 541.
• Silk, J. 1977, Ap.J. 211, 638.
• White, S.D.M. & Rees, M.J. 1978, M.N.R.A.S. 183, 341.

Last modified: April 10, 1995