HI in the galactic halo

We find solid evidence for diffuse HI gas at substantial z heights in our Galaxy, with a velocity dispersion of sigma = 60 km s(-1) and a vertical projected column density of N-Hi = 1.4 . 10(19) 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 the ground. Investigations of receiver bandpass and stray radiation effects could not explain this component as an artifact of the instrumentation. Assuming that the distribution of mass and pressure perpendicular to the galactic plane is in hydrostatic equilibrium with the galactic potential, we derive a vertical exponential scale height of h(z) similar or equal to 4.4 kpc for the observed diffuse high-dispersion HI component. The radial distribution is characterized by the corresponding galactocentric scale length A(1) similar or equal to 15 kpc.