Siegel der Universität

Universität zu Köln
Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

A string of giant molecular clouds in the south: RCW106

Printer-friendly versionPDF version

B. Mookerjea, C. Kramer, N. Volgenau,
M. Burton, I. Bains, M. Hunt (UNSW Sydney),
T. Wong, P. Jones (ATNF CSIRO)

Owing to their occurrence in more distant crowded stellar clusters, shorter formation timescales, and formation in regions of high visual extinction, the formation of massive stars is still poorly understood. Submillimeter observatories have only recently been constructed in the southern hemisphere. The new single-dish telescopes (NANTEN2, APEX, ASTE) and the soon-to-come ALMA interferometer will allow to study massive star formation in the southern hemisphere.

We have initiated a program to study the molecular cloud complex, covering a region of 28pc x 94pc, associated with the well-known southern H II region RCW 106 located at a distance of 3.6 kpc. Radio (Goss & Shaver 1970) and far-infrared (Karnik et al. 2001) continuum mapping observations, IRAS and MSX images have shown that this complex consists of a string of high mass star forming clouds.

We aim to use both sub-mm and mm dust continuum and spectroscopic observations to

  1. obtain a census of star forming cores in the region,
  2. understand the physical, chemical, and kinematic conditions of selected star forming cores and
  3. the role played by the high mass star forming cores towards triggering further star formation.

Dust continuum study using SIMBA on SEST

As a first step, we have mapped the dust continuum emission from this region at 1.2 mm using SIMBA (Mookerjea et al. 2004). The observations, having an HPBW of 24" (0.4 pc), revealed 95 clumps. The detected millimeter sources (MMS) include on one end the exotic MMS5 (associated with IRAS 16183-4958, one of the brightest infrared sources in our Galaxy) and the bright (and presumably cold) source MMS54, with no IRAS or MSX associations on the other end. Assuming a uniform dust temperature of 20 K, we estimated the total mass of the GMC associated with RCW 106 to be ~ 105 solar masses, with the constituent millimeter clumps covering a range of masses from 40 to 104 solar masses. The clump mass spectra derived using both Gaussclumps (Stutzki & Güsten 1990) and Clumpfind (Williams et al. 1994) have an index (a =1.6 ±0.3) similar to the index found from large scale CO observations (Heyer et al. 2001, Kramer et al. 1998, etc) and in contrast to the dust clump mass spectrum for low-mass cores (e.g. Testi et al. 1998, Motte et al. 2001).

Collaboration: This work has been a collaboration of B.Mookerjea and C. Kramer with M. Nielbock (Uni Bochum) and L.A. Nyman (APEX, ESO).

Spectroscopic Study of the mm-clumps in the RCW106 complex

In a follow-up collaborative effort with the star formation group of UNSW, Australia we have mapped the entire region around RCW106, using the 22m MOPRA telescope of ATNF in 13CO(1-0) (Bains et al. 2005). The beamsize of MOPRA, 33", is comparable to that of SEST. As a first step, CLUMPFIND (Williams et al. 1994) was used to decompose the 2-dimensional integrated 13CO(1-0) structure into clumps. Comparison with the clumps identified in the 1.2 mm SIMBA data and the 21µm MSX data suggest that only 50 percent of the gas clumps have an associated dust clump at either wavelength. These observations further suggest that the gas is extended and of low dynamic range whilst the dust is compact and display much higher contrast between the compact and the extended emission. The total mass detected in 13CO(1-0) is estimated to be 6 105 solar masses, similar within a factor of 2 with the mass derived from the dust map.

In a simultaneous effort to probe the nature and evolutionary stage of the 15 brightest millimeter cores detected in the 1.2 mm continuum study of the RCW106 complex, we performed a pilot chemical study between 86 and 115 GHz (Mookerjea et al. 2004b). The study was based on pointed spectroscopic observations of CO, C18O, CS, C34S, HCN, HNC, HCO+, H13CO+, N2H+ and the (2k-1k) quartet of CH3OH using the MOPRA. In addition to deriving a first estimate of the excitation temperature and column densities of the different species, the observations were aimed to obtain an overview of the strength of the various spectral lines in order to optimize future detailed mapping observations. Kinetic temperatures estimated from the CO observations lie between 20 and 70 K. Hydrogen column densities estimated from C18O lie between 1.7 and 9.7 1023 cm-2.
This project is currently closely coordinated with the UNSW star formation group and follow up mapping observations of NH3 using ATCA (to determine kinetic temperatures more accurately) will be proposed for and C18O, N2H+, HCO+, HNC and SiO using MOPRA will be observed during the next 4 months.

Collaboration: This work is a collaboration of B.Mookerjea and C.Kramer with M.G. Burton, M. Hunt, I. Bains, T. Wong (UNSW, Australia).