Submillimeter Observations of Midcourse Space Experiment Galactic Infrared-Dark Clouds

We present 850 and 450 μm continuum images of infrared-dark clouds (IRDCs) taken with the Submillimeter Common-User Bolometer Array (SCUBA) submillimeter camera at the James Clerk Maxwell Telescope. The IRDCs are large (1-10 pc diameter) molecular cores with gas densities ~10⁶ cm^-3 and temperatures ~15 K. We detected strong submillimeter sources with peak flux densities of ~1 Jy beam^-1 at 850 μm in all eight clouds that were observed. The submillimeter emission generally lies within the envelope of the mid-infrared extinction where dense gas has been detected using H₂CO as a tracer. The dust temperatures in the bright, compact sources are calculated to lie in the range 10-25 K. The masses of these sources are estimated to be in the range of several tens up to about a thousand solar masses. The corresponding gas column densities range over an order of magnitude, up to about 10²³ cm^-2. Several of the sources are detected in emission at both 850 and 8 μm. Two of the sources have HCO⁺ line profiles characteristic of molecular infall. It is likely that the bright, compact sources seen in the SCUBA images are in various early stages of star formation, from preprotostellar cores to class I objects.