Galactic disks, infall, and the global value of Omega

Details Galactic disks, infall, and the global value of Omega Galactic disks, infall, and the global value of Omega

Apr 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apj...389....5t&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 389, April 10, 1992, p. 5-26.

Astronomy and Astrophysics

Astrophysics

324

Astronomical Models, Cosmology, Galactic Structure, Milky Way Galaxy, Spiral Galaxies, Accretion Disks, Circular Orbits, Dark Matter, Galactic Evolution, Halos

Scientific paper

Stringent limits on the current rate of infall of satellite systems onto spiral galaxies are set on the basis of the thinness and coldness of Galactic disks. For infalling satellites on isotropically oriented circular orbits, it is shown that, due to scattering, the thermal energy gain of the disk exceeds the satellite energy loss from dynamical friction by a factor of 1.6, with 25 percent deposited in z motion and 75 percent in planar motions. It is found that no more than 4 percent of the Galactic mass inside the solar radius can have accreted within the last 5 billion years, or else its scale and its Toomre Q-parameter would exceed observed values. In standard cold-dark-matter-dominated models for the growth of structure with Omegatot of 1, the mass accreted in dark matter lumps rises faster than t exp 2/3 and would exceed 28 percent in the last 5 Gyr. It is proposed that heating from satellite infall accounts for a substantial fraction of the increase of velocity dispersion and scale height with age that is observed in the Galaxy.

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