A Comparison of the Velocity Fields of Young Stellar Objects and of Sharpless H II Regions

Abstract

Assuming that the motion of Galactic objects can be represented by a smoothly-varying velocity field on which is superposed a random motion, it is possible to represent the radial component of the smooth field by a formula with a small number of parameters, which can be derived from the observations by standard statistical methods. This has been performed for 1) a list of 989 O- and B-type stars in the solar neighbourhood for which the distance and radial velocity are known, and 2) a list of 112 molecular clouds for which these same quantities are known. The result is a prediction, for each class of objects, of the most probable radial velocity at an arbitrary position in the Galaxy, together with an estimate of its probable error. For the stellar objects, the result deviates only marginally from what would result from circular motion about a centre, but for the molecular clouds the result appears to imply a distorted motion.