Mid-J CO shock tracing observations of infrared dark clouds. I. A. Pon, P. Caselli, D. Johnstone, M. Kaufman, M. J. Butler, F. Fontani, I. Jiménez-Serra and J. C. Tan A&A, 577 (2015) A75 Published online: 06 May 2015 DOI: 10.1051/0004-6361/201525681