21-CM Line Observations of Galactic H II Regions

Abstract

Twenty-seven galactic H ir regions have been observed in the 21-cm spectral line using the 300-foot transit radio telescope and the 100-channel digital autocorrelator of the National Radio Astronomy Observatory. Neutral hydrogen components associated with IC 5146, NGC 281, 8170, and S222 have been detected. IC 5146 has an H i mass of 670 Mo and an H ii mass of 20 Mo, and is not a simple isolated gravitationally bound system. NGC 281 has an H i mass of at least 16000 Mo, and an H ii mass of 880 Mo. In both cases the 21-cm systemic velocity is in agreement with the optical value. IC 5146 and NGC 281 both contain star clusters, and all four objects with H i associated with them have patches of obscuration crossing them. There is no direct observational evidence for the existence of an expanding H I component containing an appreciable fraction of the observed neutral hydrogen mass in any of the cases reported. Seven high4atitude H ii regions have no neutral hydrogen associated to an upper limit of 8 K brightness temperature. The sixteen remaining H ii regions either had no clear H I features visible above the large-scale background or were located in regions so complex as to make detection impossible.