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The High-Velocity Clouds: Galactic or Extragalactic?

Published online by Cambridge University Press:  12 April 2016

Hugo van Woerden ,
Bart P. Wakker ,
Ulrich J. Schwarz ,
Reynier F. Peletier  and
Peter M.W. Kalberla
Hugo van Woerden
Affiliation:
Kapteyn Institute, Postbus 800, 9700 AV Groningen, The Netherlands
Bart P. Wakker
Affiliation:
Department of Astronomy, University of Wisconsin, Madison WI, USA
Ulrich J. Schwarz
Affiliation:
Kapteyn Institute, Postbus 800, 9700 AV Groningen, The Netherlands
Reynier F. Peletier
Affiliation:
Kapteyn Institute, Postbus 800, 9700 AV Groningen, The Netherlands
Peter M.W. Kalberla
Affiliation:
Radioastronomisches Institut der Universität, Bonn, Germany

Abstract

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We present firm evidence that one of the major high velocity clouds (HVCs), Complex A, lies in the Milky Way Halo, at a vertical distance z = 3 - 7 kpc from the Galactic plane. For clouds MII/MIII, Danly et al. and Keenan et al. had already found z < 5 kpc. We further report that the metallicity in the largest HVC, Complex C, is at least 0.1 solar. Call/Hi ratios in 6 HVCs, ranging from 0.002 to 0.07 times solar, set lower limits to their metallicities.

Blitz et al. have recently suggested that most of the HVCs are relatively unprocessed, extragalactic remnants of the gas which formed the Local Group of galaxies. However, the results mentioned above indicate that several major HVC complexes are neither primordial nor extragalactic. For the smaller HVCs, some of which have much higher velocities, a location in the Local Group remains a possibility.

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. 467 - 470
Copyright
Copyright © Springer-Verlag 1998

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