The modelling of infrared dark cloud cores

¹ Kapteyn Astronomical Institute, University of Groningen, PO box 800, 9700 AV Groningen, The Netherlands e-mail: ormel@astro.rug.nl
² SRON National Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands e-mail: [russ;f.p.helmich]@sron.rug.nl
³ Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany e-mail: ossk@ph1.uni-koeln.de

Received: 17 November 2004
Accepted: 4 May 2005

Abstract

This paper presents results from modelling and continuum and line observations of three distinct cores of an infrared dark cloud (IRDC) directed toward the W51 GMC. In the sub-mm continuum these cores appear as bright, isolated emission features. One of them coincides with the peak of extinction as measured by the Midcourse Space Experiment satellite. Detailed radiative transfer codes are applied to constrain the cores' physical conditions to address the key question: Do these IRDC-cores harbour luminous sources? The results of the continuum model, expressed in the quality-of-fit parameter, are also constrained by the absence of emission from IRAS. For the sub-mm emission peaks this shows that sources of ∼ are embedded within the cores. For the extinction peak, the combination of continuum and line modelling indicates that a heating source is present as well. Furthermore, the line model provides constraints on the clumpiness of the medium. All three cores have similar masses of about and similar density structures. The extinction peak differs from the other two cores by hosting a much weaker heating source, and the sub-mm emission core at the edge of the IRDC deviates from the other cores by a higher internal clumpiness.