MOLECULAR LINE OBSERVATIONS OF INFRARED DARK CLOUDS. II. PHYSICAL CONDITIONS

Using a source selection biased toward high-mass star-forming regions, we used a large velocity gradient code to calculate the H-2 densities and CS column densities for a sample of Midcourse Space Experiment 8 mu m infrared dark cores. Our average H-2 density and CS column density were 1.14 x 10(6)cm(-3) and 1.21 x 10(13) cm(-2), respectively. In addition, we have calculated the Jeans mass and Virial mass for each core to get a better understanding of their gravitational stability. We found that core masses calculated from observations of N2H+ J = 1 -> 0 and (CO)-O-18 J = 1 -> 0 by Ragan et al. (Paper I) were sufficient for collapse, though most regions are likely to form protoclusters. We have explored the star-forming properties of the molecular gas within our sample and find some diversity which extends the range of infrared dark clouds from the very massive clouds that will create large clusters, to clouds that are similar to some of our local counterparts (e.g., Serpens, Ophiuchus).