Mid-J CO shock tracing observations of infrared dark clouds

II. Low-J CO constraints on excitation, depletion, and kinematics^⋆,⋆⋆

¹ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
² Department of Physics and Astronomy, The University of Western Ontario, London, N6A 3K7, Canada
e-mail: apon@uwo.ca
³ Joint Astronomy Centre, 660 North A’ohoku Place, University Park, Hilo, HI 96720, USA
⁴ NRC-Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
⁵ Department of Physics and Astronomy, University of Victoria, PO Box 3055 STN CSC, Victoria, BC V8W 3P6, Canada
⁶ INAF−Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁷ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, PO Box 3-72, 58090 Morelia, Michoacán, Mexico
⁸ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁹ Department of Physics and Astronomy, San Jose State University, One Washington Square, San Jose, CA 95192-0106, USA
¹⁰ Space Science and Astrobiology Division, MS 245-3, NASA Ames Research Center, Moffett Field, CA 94035, USA
¹¹ Department of Physics and Astronomy, University College London, 132 Hampstead Road, London NW1 2PS, UK
¹² Departments of Astronomy & Physics, University of Florida, Gainesville, FL 32611, USA

Received: 10 August 2015
Accepted: 16 December 2015

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 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.