Radio continuum interferometry of dark clouds. I - A search for newly formed H II regions. II - A study of the physical properties of local newly formed H II regions

Abstract

A search for compact H II regions embedded in dark clouds has been carried out in an effort to study local massive star formation. Approximately 20% of the total area of opaque dark cloud material in the sky with A/sub v/> or =6 mag was surveyed with the NRAO three-element interferometer at 2695 MHz, and at least 5% more was surveyed with the NRAO 300-ft. telescope at 4750 MHz. The regions surveyed include the dark cloud complexes in Perseus, Taurus, Orion, and Ophiuchus, as well as several smaller cloud complexes and individual clouds. No hidden compact H II regions embedded inside dark clouds were detected with certainty in the radio continuum. However, 11 H II regions with associated visible emission and 18 other sources identified as possible H II regions were detected. Comparison of the single dish and interferometer results indicates that selection effects, which may be the result of the process of local massive star formation, were present in the survey. This paper reports the general results of the observations. Analysis of specific regions of star formation and of the selection effects is presented in two corresponding papers. The completeness and interpretation of this survey cannot be judged withoutmore » such an analysis.« less