Observations of the Hydrogen Recombination Line 158α in Galactic H II Regions

Abstract

Observations of emission in the l58a line at 1651 MHz of the hydrogen recombination spectrum in galactic H ii regions are described. For thirty-nine nebulae, twenty well-known optical objects, eighteen thermal radio sources, and one previously uncatalogued object, velocities, intensities, and line widths are reported. Thirteen of the sources lie within the Cygnus X complex. Kinematic distances and estimates of the peculiar motions of the 1111 regions are derived. Line widths are used to estimate the size of internal motions; the average of mass motions in all the nebulae is 25 km/sec. A discussion of the determination of electron temperature from the ratio of line-to-continuum emission is presented. It is found that the as- sumption of a constant temperature within an H ii region leads to the measurement of too low a tem- perature by this radio method. No definite conclusion concerning the presence of non-equilibrium effects is reached. I. INTRODUCTIO