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The Galactic HI Halo

Published online by Cambridge University Press:  12 April 2016

P.M.W. Kalberla ,
G. Westphalen ,
U. Mebold ,
D. Hartmann  and
W.B. Burton
P.M.W. Kalberla
Affiliation:
Radioastronomisches Institut der Universität Bonn, 53121 Bonn, Germany
G. Westphalen
Affiliation:
Radioastronomisches Institut der Universität Bonn, 53121 Bonn, Germany
U. Mebold
Affiliation:
Radioastronomisches Institut der Universität Bonn, 53121 Bonn, Germany
D. Hartmann
Affiliation:
Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, U.S.A.
W.B. Burton
Affiliation:
Sterrewacht Leiden, P.O. Box 9513, RA 2300 Leiden, The Netherlands

Abstract

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We find indications for diffuse HI gas at substantial z heights in our Galaxy, with a velocity dispersion of 60 km s−1 and a vertical projected column density of 1.41019 cm−2. This pervasive component of the emission spectrum could be identified in the Leiden/Dwingeloo 21 cm Survey (LDS) after increasing the accuracy further by correcting the observations for reflections from ground. Assuming hydrostatic equilibrium an exponential scale height of 4.4 kpc for the observed diffuse high-dispersion Hi component is deduced. This differs from the scale height of lkpc derived by Lockman & Gehman (1991), which corresponds to a velocity dispersion of 34kms−1, based on an analysis of the the Bell Laboratories HI Survey (BLS). A comparison of BLS and LDS data explains the differences in the derived model parameters in terms of baseline uncertainties at a level of ≈ 30 mK. We find additional indications for baseline uncertainties in the BLS data. Concerning the LDS we cannot, however, exclude that this survey may also be affected by baseline uncertainties. Receiver bandpass and stray-radiation effects need a more thorough analysis before drawing firm conclusions.

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. 479 - 482
Copyright
Copyright © Springer-Verlag 1998

References

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