Mid-J CO shock tracing observations of infrared dark clouds. II. Low-J CO constraints on excitation, depletion, and kinematics

Abstract

Infrared dark clouds are kinematically complex molecular structures in the interstellar medium that can host sites of massive star formation. We present maps measuring 4 square arcminutes of the <SUP>12</SUP>CO, <SUP>13</SUP>CO, and C<SUP>18</SUP>O 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 <SUP>13</SUP>CO and C<SUP>18</SUP>O 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. <P />Based on observations carried out with the JCMT and IRAM 30 m Telescopes. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).IRAM CO observations are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A96">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A96