Galactic winds. II. Role of the disk-halo interface in cosmic ray driven galactic winds.
Abstract
By emphasizing the dynamical role of Cosmic Rays (CRs) in galactic haloes, it is argued that the region can be divided into a lower part where CR diffusion prevails and upper part which is the site of galactic wind formation due to a strong coupling between the CRs and self-excited hydromagnetic waves. A stationary but nonstatic model for the lower halo is described in which the thermal and the CR pressure push the gas against a gravitational pull which can either increase with distance from the disk or remain approximately constant. We present analytical solutions for typical disk parameters such as gas density, gas and CR pressure, appropriate for the Galaxy, and show that it is possible to match them to the outflow solutions in the upper halo. It turns out that the flow of the disk-halo interlace is always subsonic. In order to obtain physically reasonable velocity profiles in that region, we find that the observationally permitted range of mass loading is considerably restricted. The effect of the CRs on the flow is that for a diffusion coefficient less than critical the halo density exhibits a maximum. The problem of stability of these stationary solutions is also discussed within the context of overturning and cooling.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- March 1993
- Bibcode:
- 1993A&A...269...54B
- Keywords:
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- Galactic Cosmic Rays;
- Galactic Halos;
- Interstellar Gas;
- Molecular Gases;
- Gas Pressure;
- Hydrogen;
- Interstellar Magnetic Fields;
- Astrophysics