The structure and kinematics of dense gas in NGC2068

Abstract

We have carried out a survey of the NGC2068 region in the Orion B molecular cloud using HARP on the James Clerk Maxwell Telescope, in the 13CO and C18O (J = 3-2) and H13CO+ (J = 4-3) lines. We used 13CO to map the outflows in the region, and matched them with previously defined Submillimetre Common-User Bolometer Array cores. We decomposed the C18O and H13CO+ into Gaussian clumps, finding 26 and eight clumps, respectively. The average deconvolved radii of these clumps are 6200 ± 2000 and 3600 ± 900 au for C18O and H13CO+, respectively. We have also calculated virial and gas masses for these clumps, and hence determined how bound they are. We find that the C18O clumps are more bound than the H13CO+ clumps (average gas mass to virial mass ratio of 4.9 compared to 1.4). We measure clump internal velocity dispersions of 0.28 ± 0.02 and 0.27 ± 0.04 km s-1 for C18O and H13CO+, respectively, although the H13CO+ values are heavily weighted by a majority of the clumps being protostellar, and hence having intrinsically greater linewidths. We suggest that the starless clumps correspond to local turbulence minima, and we find that our clumps are consistent with formation by gravoturbulent fragmentation. We also calculate interclump velocity dispersions of 0.39 ± 0.05 and 0.28 ± 0.08 km s-1 for C18O and H13CO+, respectively. The velocity dispersions (both internal and external) for our clumps match results from numerical simulations of decaying turbulence in a molecular cloud. However, there is still insufficient evidence to conclusively determine the type of turbulence and time-scale of star formation, due to the small size of our sample. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.