A CO survey on a sample of Herschel cold clumps^⋆

¹ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, 1121 Budapest, Konkoly Thege Miklós út 15-17, Hungary
e-mail: feher.orsolya@csfk.mta.hu
² Eötvös Loránd University, Department of Astronomy, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
³ Department of Physics, PO Box 64, 00014 University of Helsinki, Finland
⁴ Institut UTINAM – UMR 6213, CNRS, Univ. Bourgogne Franche Comté, 41bis avenue de l’Observatoire, 25000 Besançon, France
⁵ Chalmers University of Technology, Department of Earth and Space Sciences, Onsala Space Observatory, 439 92 Onsala, Sweden
⁶ Université de Toulouse, UPS-OMP, IRAP, 31400 Toulouse, France
⁷ CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
⁸ Department of Physical Science, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan
⁹ Chile Observatory, National Astronomical Observatory of Japan, National Institutes of Natural Science, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

Received: 9 October 2016
Accepted: 21 August 2017

Abstract

Context. The physical state of cold cloud clumps has a great impact on the process and efficiency of star formation and the masses of the forming stars inside these objects. The sub-millimetre survey of the Planck space observatory and the far-infrared follow-up mapping of the Herschel space telescope provide an unbiased, large sample of these cold objects.

Aims. We have observed ¹²CO(1−0) and ¹³CO(1−0) emission in 35 high-density clumps in 26 Herschel fields sampling different environments in the Galaxy. Here, we aim to derive the physical properties of the objects and estimate their gravitational stability.

Methods. The densities and temperatures of the clumps were calculated from both the dust continuum and the molecular line data. Kinematic distances were derived using ¹³CO(1−0) line velocities to verify previous distance estimates and the sizes and masses of the objects were calculated by fitting 2D Gaussian functions to their optical depth distribution maps on 250 μm. The masses and virial masses were estimated assuming an upper and lower limit on the kinetic temperatures and considering uncertainties due to distance limitations.

Results. The derived excitation temperatures are between 8.5−19.5 K, and for most clumps between 10−15 K, while the Herschel-derived dust colour temperatures are more uniform, between 12−16 K. The sizes (0.1−3 pc), ¹³CO column densities (0.5−44 × 10¹⁵ cm^-2) and masses (from less than 0.1 M_⊙ to more than 1500 M_⊙) of the objects all span broad ranges. We provide new kinematic distance estimates, identify gravitationally bound or unbound structures and discuss their nature.

Conclusions. The sample contains objects on a wide scale of temperatures, densities and sizes. Eleven gravitationally unbound clumps were found, many of them smaller than 0.3 pc, but large, parsec-scale clouds with a few hundred solar masses appear as well. Colder clumps have generally high column densities but warmer objects appear at both low and higher column densities. The clump column densities derived from the line and dust observations correlate well, but are heavily affected by uncertainties of the dust properties, varying molecular abundances and optical depth effects.