Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...311..113z&link_type=abstract
Astronomy and Astrophysics, v.311, p.113-126
Astronomy and Astrophysics
Astrophysics
72
Galaxies: Halo, Galaxy: Halo, Cosmic Rays, Galaxies: Magnetic Field, Mhd
Scientific paper
We have calculated the dynamics of mass loss from a disk galaxy with the escaping high energy component of the ISM (cosmic rays), and the magnetic field. The coupling between cosmic rays and plasma is provided by the resonant excitation of small-scale magnetic field fluctuations (MHD waves). Earlier work is generalized by including galactic rotation and the resulting magnetic tension of the frozen-in field. It is shown that nonlinear damping of self-excited waves in the galactic halo is significant, thus heating the plasma. We obtain steady-state galactic wind solutions with a moderate enhancement of the galactic mass loss rate in comparison with a non-rotating and undamped model. A qualitative new result of this theory is the determination of the angular momentum loss rate of a galaxy. Due to magnetic stresses, this exceeds the angular momentum carried away by the fluid elements leaving the galaxy. Thus the halo is forced to corotate with the disk up to a vertical distance of a few kiloparsecs, typically. Quantitatively, for our Galaxy, we find that over a Galactic evolution time scale of 10^10^ years about 17 to 39 percent of the total angular momentum (including the stellar component) is lost. The corresponding numbers due to magnetic stresses alone are about 2 to 17 percent. Since the star formation rate is likely to have been significantly larger in the past, it seems inevitable that galaxies like ours have lost a significant amount of their present angular momentum.
Breitschwerdt Dieter
Ptuskin Vladimir S.
Voelk Heinrich J.
Zirakashvili Vladimir N.
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