1 Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
2 Max-Planck Institute für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
3 Observatorio Astronomico Nacional (OAN-IGN), Alfonso XII 3, 28014, Madrid, Spain
Received: 3 March 2015
Accepted: 19 November 2015
Filaments play a central role in the molecular clouds’ evolution, but their internal dynamical properties remain poorly characterized. To further explore the physical state of these structures, we have investigated the kinematic properties of the Musca cloud. We have sampled the main axis of this filamentary cloud in 13CO and C18O (2–1) lines using APEX observations. The different line profiles in Musca shows that this cloud presents a continuous and quiescent velocity field along its ~6.5 pc of length. With an internal gas kinematics dominated by thermal motions (i.e. σNT/cs ≲ 1) and large-scale velocity gradients, these results reveal Musca as the longest velocity-coherent, sonic-like object identified so far in the interstellar medium. The transonic properties of Musca present a clear departure from the predicted supersonic velocity dispersions expected in the Larson’s velocity dispersion-size relationship, and constitute the first observational evidence of a filament fully decoupled from the turbulent regime over multi-parsec scales.
Key words: radio lines: ISM / ISM: clouds / ISM: kinematics and dynamics / ISM: molecules / ISM: structure
This publication is based on data acquired with the Atacama Pathfinder Experiment (APEX). APEX is a collaboration between the Max-Planck-Institut fuer Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory (ESO programme 087.C-0583).
The reduced datacubes as FITS files are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A97
© ESO, 2016