Recombination Lines from Compact HII Regions

Extract

Radio recombination lines of hydrogen (H167ot) have been observed from 45 HII regions using the Arecibo telescope. Nine of these sources also show the C167a line, and twenty show H2103 lines. Some of the carbon lines, particularly those from W48 and G62.2 + 0.5, show a significant negative displacement from the H167a velocities. This can be explained if the lines originate in the ionization front or in neutral material swept up by the ionization front. The displacement is 3.8 km/sec for W48, and 5.7 km/sec for G62.2 + 0.5. The source G37.7 + 0.1 ex-hibited two H167a lines, one 25 km/sec wide at 87.3 km/sec and one 16 km/sec wide at 48 km/sec, velocities with respect to the local standard of rest. This may be a case of two HII regions in the same line of sight. Parameters for the HII regions, such as electron temperatures and densities, are derived. (Paper to appear in the Astronomical Journal.)