H I shells and supershells

Abstract

Photographic representations of H I antenna temperatures in narrow velocity intervals vs galactic longitude and latitude are presented for velocities of -143 to +141 km/s, longitudes of 10 to 250 deg, and latitudes of -10 to +10 deg. A multitude of structure, much of which is filamentary, is observed in the photographs. Forty-six stationary H I shells and 17 expanding H I shells are identified, and properties of these shells are tabulated. Distances to the shells and the velocity dispersion are estimated, along with the hydrogen content of the H I shells and the energies of the expanding shells. The results are compared with previous studies, the numbers and production rates of H I shells are considered, and explanations are offered for the observed shapes of the shells. Eleven 'supershells' are identified, and possible production agents for these shells are examined.