Milky Way Disk-Halo Transition in HI: Properties of the Cloud Population

Understand

Using 21cm HI observations from the Parkes Radio Telescope's Galactic All-Sky Survey, we measure 255 HI clouds in the lower Galactic halo that are located near the tangent points at 16.9 < l < 35.3 degrees and |b| < 20 degrees.

• The clouds have a median mass of 700 Msun and a median distance from the Galactic plane of 660 pc.
• This first Galactic quadrant (QI) region is symmetric to a region of the fourth quadrant (QIV) studied previously using the same data set and measurement criteria.
• The properties of the individual clouds in the two quadrants are quite similar suggesting that they belong to the same population, and both populations have a line of sight cloud-cloud velocity dispersion of sigma_cc ~ 16 km/s.