A kinematic study of galactic HII regions. Indication of a contraction towards the center

Abstract

We have considered radial velocities of galactic H II regions with known distances to analyze the velocity field of these regions along the galactic plane. A radial velocity is taken as the average of optical and radio data existing in the literature. A limiting value of 14 km kpc−1 s−1 for Oort’s constant A is attained with a least squares solutions, as we incorporate regions with ever larger distances from the sun. The data also suggest an overall radial contraction of the H II regions towards the galactic center of about 6 km s−1.