|
Infrared Dark Clouds are identified as deep extinction features against the Galactic mid-infrared background. Through 13CO and CS observations, we have determined kinematic distances to over 500 IRDCs. We find characteristic sizes of several pc and masses of a few thousand M_sun, comparable to cluster-forming molecular clumps like Orion and Ophiucus. Millimeter continuum images show that IRDCs contain compact cores with sizes <0.5 pc and masses ~ 100 M_sun. About 1/3 of these cores show unambiguous evidence for active star formation, such as outflows, high densities, broad lines,
evidence for shocks, and "hot core" chemistry. Several have luminosities >10,000 L_sun, conclusively demonstrating that they contain high-mass protostars. Interferometeric images often reveal binary or multiple protostellar systems, indicating cluster formation. The "quiescent" IRDC cores are probably high-mass
"starless cores."
|