The Distribution of Disk-Halo HI Clouds in the Inner Milky Way

Studies by Ford et al., concerning the physical properties and distribution of HI clouds in the inner Milky Way using 21 cm HI observations from the Parkes Radio Telescope’s Galactic All-Sky Survey, are reviewed. Individual clouds were identified in regions centered on tangent points at galactic longitudes 25 (quadrant I; hereafter Q1) and 335 (quadrant IV; hereafter QIV) and within 20 of the galactic plane. Clouds in the two regions have similar physical properties and random velocities relative to galactic rotation but are 3 times more populous with double the scale height in QI than in QIV. These asymmetries are attributed to their formation from gas lifted from star formation regions of the spiral arms in the disc by superbubbles and stellar feedback or from fragmenting supershells. Subject headings: Milky Way, HI clouds