Mid-J CO shock tracing observations of infrared dark clouds II Low-J CO
  constraints on excitation, depletion, and kinematics
  Infrared dark clouds are kinematically complex molecular structures in the
interstellar medium that can host sites of massive star formation. We present 4
square arcminute maps of the 12CO, 13CO, and C18O J = 3 to 2 lines from
selected locations within the C and F (G028.37+00.07 and G034.43+00.24)
infrared dark clouds (IRDCs), as well as single pointing observations of the
13CO and C18O J = 2 to 1 lines towards three cores within these clouds. We
derive CO gas temperatures throughout the maps and find that CO is
significantly frozen out within these IRDCs. We find that the CO depletion
tends to be the highest near column density peaks, with maximum depletion
factors between 5 and 9 in IRDC F and between 16 and 31 in IRDC C. We also
detect multiple velocity components and complex kinematic structure in both
IRDCs. Therefore, the kinematics of IRDCs seem to point to dynamically evolving
structures yielding dense cores with considerable depletion factors.
