We present an investigation of candidate Infrared Dark Cloud cores as identified by located within the SCUBA Legacy Catalogue .
After applying a uniform noise cut to the Catalogue data we identify 154 Infrared Dark Cloud cores that were detected at 850 \mu m and 51 cores that were not .
We derive column densities for each core from their 8 \mu m extinction and find that the IRDCs detected at 850 \mu m have higher column densities ( a mean of 1.7 \times 10 ^ { 22 } cm ^ { -2 } ) compared to those cores not detected at 850 \mu m ( a mean of 1.0 \times 10 ^ { 22 } cm ^ { -2 } ) .
Combined with sensitivity estimates , we suggest that the cores not detected at 850 \mu m are low mass , low column density and low temperature cores that are below the sensitivity limit of SCUBA at 850 \mu m. For a subsample of the cores detected at 850 \mu m those contained within the MIPSGAL area ) we find that two thirds are associated with 24 \mu m sources .
Cores not associated with 24 \mu m emission are either “ starless ” IRDC cores that perhaps have yet to form stars , or contain low mass YSOs below the MIPSGAL detection limit .
We see that those “ starless ” IRDC cores and the IRDC cores associated with 24 \mu m emission are drawn from the same column density population and are of similar mass .
If we then assume the cores without 24 \mu m 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 10 ^ { 3 } –10 ^ { 4 } years .
Finally , we make conservative predictions for the number of observed IRDCs that will be observed by the Apex Telescope Galactic Plane Survey ( ATLASGAL ) , the Herschel Infrared Galactic Plane Survey ( Hi-GAL ) , the JCMT Galactic Plane Survey ( JPS ) and the SCUBA-2 “ All Sky ” Survey ( SASSy ) .