Submillimeter observations of Midcourse Space Experiment galactic infrared-dark clouds

We present 850 and 450 mum continuum images of infrared-dark clouds (IRDCs) taken with the Submillimeter Common-User Bolometer Array (SCUBA) submillim eter camera at the James Clerk Maxwell Telescope. The IRDCs are large (1-10 pc diameter) molecular cores with gas densities similar to 10(6) cm(-3) an d temperatures approximate to 15 K. We detected strong submillimeter source s with peak flux densities of approximate to1 Jy beam(-1) at 850 mum in all eight clouds that were observed. The submillimeter emission generally lies within the envelope of the mid-infrared extinction where dense gas has bee n detected using H2CO as a tracer. The dust temperatures in the bright, com pact sources are calculated to lie in the range 10-25 K. The masses of thes e sources are estimated to be in the range of several tens up to about a th ousand solar masses. The corresponding gas column densities range over an o rder of magnitude, up to about 10(23) cm(-2). Several of the sources are de tected in emission at both 850 and 8 mum 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 sta r formation, from preprotostellar cores to class I objects.