Global properties of the HI distribution in the outer Milky Way - Planar and extra-planar gas

Context. The determination of the global structure of the planar and extra-planar Milky Way H I disk depends critically on a reliable database but also on reasonable assumptions about the shape of the Milky Way rotation curve. Aims. We derive the 3D H I volume density distribution for the Galactic disk out to R similar to 60 kpc. Methods. Our analysis is based on parameters for the warp and rotation curve derived previously. The data are taken from the Leiden/Argentine/Bonn all sky 21 cm line survey. Results. The Milky Way H I disk is significantly warped but shows a coherent structure out to R similar to 35 kpc. The radial surface density distribution, the densities in the middle of the warped plane, and the H I scale heights all follow exponential relations. The radial scale length for the surface density distribution of the H I disk is 3.75 kpc. Gas at the outskirts for 40 less than or similar to R less than or similar to 60 kpc is described best by a distribution with an exponential radial scale length of 7.5 kpc and a velocity dispersion of 74 km s(-1). Such a highly turbulent medium fits also well with the average shape of the high velocity profile wings observed at high latitudes. The turbulent pressure gradient of such extra-planar gas is on average in balance with the gravitational forces. About 10% of the Milky Way H I gas is in this state. The large scale H I distribution is lopsided; for R greater than or similar to 15 kpc there is more gas in the south. The H I flaring indicates that this asymmetry is caused by a dark matter wake, located at R similar to 25 kpc in direction of the Magellanic System. Conclusions. The H I disk is made up of two major components. Most prominent is the normal H I disk which can be traced to R similar to 35 kpc. this is surrounded by a patchy distribution of highly turbulent gas reaching large scale heights but also large radial distances. At the position of the Sun the exponential scale height in the z direction is 3.9 kpc. This component resembles the anomalous gas discovered previously in some galaxies.