A multiwavelength study of the S106 region

I. Structure and dynamics of the molecular gas

¹ I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
² IRAM, BP 53, 38406 Saint Martin d'Hères, France
³ Observatoire de Bordeaux, BP 89, 33270 Floirac, France
⁴ Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA

Corresponding author: N. Schneider, schneider@observ.u-bordeaux.fr

Received: 7 September 2001
Accepted: 15 January 2002

Abstract

The molecular cloud associated with Sharpless 106 has been studied in a variety of (sub)millimeter CO rotational lines on angular resolution scales from 11'' to 80''. We used the KOSMA 3 m telescope to obtain an extended ¹²CO 2 map, from which we calculate a total mass of 2000  and an average density of  cm^-3 for the molecular cloud. The peak intensity region around the massive young star S106 IR was observed in ¹³CO 5 and 32 with KOSMA and in isotopomeric low-J CO lines with the IRAM 30 m telescope. A clump decomposition made for several lines yields a common clump-mass spectral index of , illustrating the self-similarity of the detected structures for length-scales from 0.06 to 0.9 parsec. All ¹²CO and ¹³CO line profiles within approximately 2' around S106 IR show blue wing emission and less prominent red wing emission, partly affected by self-absorption in colder foreground material. We attribute this high-velocity emission to the ionized wind of S106 IR driving a shock into the inhomogeneous molecular cloud. We do not find evidence for a smooth or fragmented disk around S106 IR and/or an expanding ring in the observed CO emission distribution. The excitation conditions along a cut through the molecular cloud/H II region are studied with an LTE analysis (and an Escape Probability model at the position of S106 IR), using the observed CO line intensities and ratios. The kinetic gas temperature is typically 40 K, the average density of the cloud in the core region is  cm^-3, and the local density within the clumps is  cm^-3. The ¹³CO/C¹⁸O line and column density ratios away from S106 IR reflect the natural isotopic abundance but towards the optical lobes and the cavity walls, we see enhanced ¹³CO emission and abundance with respect to C¹⁸O. This shows that selective photo-dissociation is only important close to S106 IR and in a thin layer of the cavity walls. In combination with the results from the excitation analysis we conclude that the molecular line emission arises from two different gas phases: (i) rather homogeneous, low- to medium-density, spatially extended clumps and (ii) embedded, small (≪0.2 pc), high-density clumps with a low volume filling factor.