Search for CO outflows toward a sample of 69 high-mass protostellar candidates: Frequency of occurrence

A survey for molecular outflows was carried out by mapping the CO J = 2-1 line toward a sample of 69 luminous IRAS point sources. Sixty objects have IRAS luminosities from 10(3) to 10(5) L, and are associated with dense gas traced by NH,, identifying them as high-mass star-forming regions. Among 69 sources, 65 sources have data that are suitable for outflow identification. Thirty-nine regions show spatially confined high-velocity wing emission in CO, indicative of molecular outflows. Most objects without identifiable outflows Lie within 0 degrees < l < 50 degrees where outflow signatures are confused by multiple cloud components along the line of sight. Excluding 26 sources with 0 degrees < l < 50 degrees, we found 35 outflows out of 39 sources, which yields an outflow detection/rate of 90%. Many of the outflows contain masses of more than 10 M. and have momenta of a few hundred M. km s(-1), at least 2 orders of magnitude larger than those in typical low-mass outflows. This class of massive and energetic outflows is most likely driven by high-mass young stellar objects. The high detection rate indicates that molecular outflows are common toward high-mass young stars. Given the connection between outflows and accretion disks in low-mass stars, we suggest that high-mass stars may form via an accretion-outflow process, similar to their low-mass counterparts.