Infrared dark cloud cores in the SCUBA Legacy Catalogue

We present an investigation of candidate infrared dark cloud (IRDC) cores as identified by Simon et al. located within the Submillimetre Common User Bolometer Array (SCUBA) Legacy Catalogue. After applying a uniform noise cut to the catalogue data, we identify 154 IRDC cores that were detected at 850μm and 51 cores that were not. We derive column densities for each core from their 8μm extinction and find that the IRDCs detected at 850μm have higher column densities (a mean of 1.7 × 10²²cm^-2) compared to those cores not detected at 850μm (a mean of 1.0 × 10²²cm^-2). Combined with sensitivity estimates, we suggest that the cores not detected at 850μm are low-mass, low-column-density and low-temperature cores that are below the sensitivity limit of SCUBA at 850μm. For a subsample of the cores detected at 850μm [those contained within the Multiband Imaging Photometer for Spitzer Galactic Plane Survey (MIPSGAL) area], we find that two-thirds are associated with 24μm sources. Cores not associated with 24μm emission are either `starless' IRDC cores that perhaps have yet to form stars, or contain low-mass young stellar objects below the MIPSGAL detection limit. We see that those `starless' IRDC cores and the IRDC cores associated with 24μm emission are drawn from the same column density population and are of similar mass. If we then assume the cores without 24μm embedded sources are at an earlier evolutionary stage to cores with embedded objects, we derive a statistical lifetime for the quiescent phase of a few 10³-10⁴yr. Finally, we make conservative predictions for the number of observed IRDCs that will be observed by the Apex Telescope Galactic Plane Survey, the Herschel Infrared Galactic Plane Survey, the James Clerk Maxwell Telescope Galactic Plane Survey and the SCUBA-2 `All Sky' Survey (SASSy).