Stellar kinematics and interstellar turbulence

Abstract

Data assembled from a variety of sources show that the velocity dispersion of young stars and cool interstellar gas increases systematically with the size of the region considered, over a wide range of length scales. This causes an increase of stellar velocity dispersion with age for stars observed near the sun, since the older stars originate from a large volume of space. This effect is sufficient to account for the observed age dependence of the velocity dispersion of stars for ages up to about 109 yr, implying that secular acceleration is relatively unimportant for the kinematics of the stars. The observed dependence of the gaseous velocity dispersion on region size suggests a turbulent hierarchy of motions in which smaller-scale motions are produced by the turbulent decay of larger-scale ones. Some of the observed large-scale motions, especially those associated with warps of the gas layer, may be driven by gas infall.