Discovery of a Population of H [CSC]i[/CSC] Clouds in the Galactic Halo

A population of discrete HI clouds in the halo of the inner Galaxy has beendiscovered in 21cm observations made with the Green Bank Telescope. The haloclouds are seen up to 1.5 kpc from the Galactic plane at many longitudes. Theirvelocities follow Galactic rotation. A group of clouds chosen for detailedstudy are found to have, in the median, a peak NHI of 2x10^19, a diameter of afew tens of pc, a density of a few tenths cm^-3, and a mass in HI of 50 solarmasses. Some halo clouds have narrow lines implying that their temperature mustbe <1000 K; some have a core-halo spectral structure. As much as half of themass of the neutral halo may reside in these discrete clouds. They may havebeen formed in a Galactic fountain and are now returning to the disk.Comment: Accepted for publication in ApJ(Letters). The 12 pages include 3 figure