Peter Kalberla (University of Bonn, Germany)

Global properties of the HI distribution in the Milky Way. Planar and extra-planar gas - Peter Kalberla Colloquium

ATNF Marsfield Lecture Theatre

Abstract

The aim of this talk is to review the global structure of the Milky Way HI disk and to disentangle contributions from the planar and extra-planar components. 90% of the HI gas is confined within a thin disk with a two-phase structure (cold and warm neutral medium). This disk is warped and the HI scale height is strongly flaring. The radial distributions of surface and mid-plane densities decrease exponentially. The gaseous disk has an extension of 35 kpc, a scale length that may be explainable by the Milky Way mass distribution. 10% of the HI gas is "anomalous", located above the plane and best described by a thick disk with a scale height exceeding the thin disk by a factor of ten. Most of this gas is in clumps, having a core-envelope structure. The clumps are probably in pressure equilibrium with a confining hot ionised medium. The halo gas is essentially co-rotating, but increasingly lagging behind the disk with increasing scale height.