Criteria for quasi-stationary collapse of a cloudy protogalaxy. I. Gravitationally stable clouds

Details Criteria for quasi-stationary collapse of a cloudy protogalaxy. I. Gravitationally stable clouds Criteria for quasi-stationary collapse of a cloudy protogalaxy. I. Gravitationally stable clouds

Jul 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998newar..42...23m&link_type=abstract

New Astronomy Reviews, Volume 42, Issue 1, p. 23-40.

Astronomy and Astrophysics

Astronomy

Scientific paper

This paper seeks to study the collapse of a non-rotating protogalaxy comprising clouds and intercloud gas. The gravitational force in it is balanced by the temperature of the gas and the random motion of the clouds. The clouds are assumed to be identical, gravitationally stable and in pressure equilibrium with the intercloud gas. The opacity, cloud evaporation by thermal conductivity, thermal instability and radiation cooling of the gas of the clouds are ignored. A system can be defined as quasi-stationary only if the free-fall time (t_ff) is smaller than both the cooling time of the gas (t_cool) and the collision time of the clouds (t_c). A study of different initial conditions of the dark and the baryonic matter was made. The important results obtained are as follows: 1. The dark matter plays a crucial role. Its amount and mass distribution strongly affect the evolution of the system. A system with a more massive and more compact dark halo has a better chance of being quasi-stationary. 2. The systems with larger masses or intermediate values of the ratio M_cl/M_g have better chances of being quasi-stationary. 3. Every spiral and dwarf elliptical galaxy formed by the collapse of a cloudy protogalaxy has passed through a phase where at least some of its layers were in a state of non-stationary collapse. 4. A giant elliptical galaxy can be formed by a quasi-stationary collapse only in a hot dark matter dominated universe. 5. The cooling flows of the hot coronas of elliptical galaxies and the intergalactic gas are probably quasi-stationary. 6. The model can explain many properties of the halo of our Galaxy.

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