ATNF Marsfield Lecture Theatre

Peter Kalberla

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

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.