1 Astrophysics and Planetary Science, The Niels Bohr Institute, Faculty of Science, Københavns Universitet2 Natural History Museum of Denmark, Faculty of Science, Københavns Universitet3 Natural History Museum of Denmark, Natural History Museum of Denmark, Faculty of Science, Københavns Universitet4 Chalmers University of Technology5 Stockholm University6 INAF - Osservatorio Astrofisico di Arcetri7 LERMA, Observatoire de Paris8 Peking University9 Harvard-Smithsonian Center for Astrophysics10 INAF, Osservatorio Astronomico di Roma11 Observatorio Astronómico Nacional (IGN)12 Astrophysics and Planetary Science, The Niels Bohr Institute, Faculty of Science, Københavns Universitet
CO line mapping at high spatial and spectral resolution
Context. The HH 54 shock is a Herbig-Haro object, located in the nearby Chamaeleon II cloud. Observed CO line profiles are due to a complex distribution in density, temperature, velocity, and geometry. Aims. Resolving the HH 54 shock wave in the far-infrared (FIR) cooling lines of CO constrain the kinematics, morphology, and physical conditions of the shocked region. Methods. We used the PACS and SPIRE instruments on board the Herschel space observatory to map the full FIR spectrum in a region covering the HH 54 shock wave. Complementary Herschel-HIFI, APEX, and Spitzer data are used in the analysis as well. The observed features in the line profiles are reproduced using a 3D radiative transfer model of a bow-shock, constructed with the Line Modeling Engine code (LIME). Results. The FIR emission is confined to the HH 54 region and a coherent displacement of the location of the emission maximum of CO with increasing J is observed. The peak positions of the high-J CO lines are shifted upstream from the lower J CO lines and coincide with the position of the spectral feature identified previously in CO (10−9) profiles with HIFI. This indicates a hotter molecular component in the upstream gas with distinct dynamics. The coherent displacement with increasing J for CO is consistent with a scenario where IRAS12500 – 7658 is the exciting source of the flow, and the 180 K bow-shock is accompanied by a hot (800 K) molecular component located upstream from the apex of the shock and blueshifted by −7 km s-1. The spatial proximity of this knot to the peaks of the atomic fine-structure emission lines observed with Spitzer and PACS ([O i]63, 145 μm) suggests that it may be associated with the dissociative shock as the jet impacts slower moving gas in the HH 54 bow-shock.