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The Galactic Halo in Hydrostatic Equilibrium

Published online by Cambridge University Press:  12 April 2016

P.M.W. Kalberla ,
J. Pietz  and
J. Kerp
P.M.W. Kalberla
Affiliation:
Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
J. Pietz
Affiliation:
Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
J. Kerp
Affiliation:
Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany

Abstract

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The large scale distribution of gas, magnetic field and cosmic rays in the Galaxy is explored. We analyze recent all-sky surveys of HI gas (Leiden/Dwingeloo survey), soft X-ray radiation (ROSAT) and high energy gamma-rays (EGRET > 100 MeV) in combination with the 408 MHz survey. Prom these observations we derive a Galactic halo model consistent with hydrostatic equilibrium conditions.

The large scale equilibrium configuration consists of two separate domains with different properties and scale sizes:

  1. 1) The gaseous halo consists of collisionally ionized gas at T=106.2K as well as HI and has an exponential scale height hz ~ 4.4 kpc. The radial distribution is characterized by the galactocentric scale length A1 ~ 15 kpc. All components of the halo – gas, magnetic field and cosmic rays – contribute equally to the pressure. The magnetic field in the halo is oriented parallel to the Galactic plane.

  2. 2) The disk extends up to a scale height of hz ~ 1 kpc and is associated with irregular magnetic fields. Here the pressure of the magnetic field is only ⅓ of the gas pressure. The cosmic rays are only weakly coupled to the disk.

Type
Part VIII High-Velocity Clouds, Galactic Halo Models, Observations of the LMC
Information
International Astronomical Union Colloquium , Volume 166: The Local Bubble and Beyond , 1997 , pp. 475 - 478
Copyright
Copyright © Springer-Verlag 1998

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