A high-resolution 21 centimeter line study of infrared cirrus

Abstract

High-resolution H I observations of part of an IR cirrus in Ursa Major are discussed. The atomic hydrogen component presents an intricate morphology and velocity field. The H I feature is made up of interconnecting filaments and condensations the majority of which have an east-west alignment. Two filaments extrude perpendicularly from the main body of the feature. The vast majority of the H I spectra have multiple components with FWHM of the order of 3-5 km/s. The velocity dispersions are about equal to the Alfven speed. The turbulent and magnetic pressures are the main forces acting on the H I gas. In IR maps, the atomic cloud appears spatially connected to a molecular cloud with a gas density one order of magnitude larger and a turbulent energy one order of magnitude smaller. The association and the location of the whole object within a large H I loops suggests that a molecular cloud is being formed or disrupted.