Astron. Astrophys. 336, 991-1006 (1998)

A survey for dense cores and young stellar clusters in the W 3 giant molecular cloud

A.R. Tieftrunk ^{1, 2}, S.T. Megeath ^{3, 4}, T.L. Wilson ^{1, 5} and J.T. Rayner <sup>6

1</sup> Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
² ESO/La Silla, Casilla 19001, Santiago 19, Chile
³ Harvard Smithsonian Center for Astrophysics, 60 Garden St. MS-72, Cambridge, MA 02138, USA
⁴ MIT Haystack Observatory, Off Route 40, Westford, MA 01886, USA
⁵ Sub-Millimeter Telescope Observatory, University of Arizona, Tucson, AZ 85721, USA
⁶ Institute for Astronomy, University of Hawaii, 2680 Woodlawn Dr., Honolulu, HI 96822, USA

Received 2 June 1997 / Accepted 27 April 1998

Abstract

We simultaneously mapped the metastable (J,K) = (1,1) and (2,2) inversion lines of toward W 3 Main, W 3(OH), and the region between these two star-forming clouds with a angular resolution using the 100-m Effelsberg telescope. We observed a 120 square-arcminute region with spacing and a significantly higher sensitivity than previous maps. We also measured the (J,K) = (3,3) line of in 28 positions toward W 3 Main. For comparison with our survey, we present a -band (2.1 µm) survey conducted by J. T. Rayner. The -band survey detects five distinct stellar clusters within the mapped region. In addition, we compare the survey to the CO (1-0) maps of the FCRAO 2nd quadrant survey (Heyer et al. 1998) and to the distribution of H II regions.

The goals of this new survey are to a) map the extent of dense gas in the W 3 Main and W 3(OH) molecular clouds, b) search for previously undetected molecular cores in the intervening molecular cloud, c) measure column densities and for regions of strong emission, d) compare the distribution of the emission to that of the CO emission and e) study the relationship between the ammonia gas and sites of star formation as traced by stellar clusters and H II regions.

In the W 3 Main cloud, we find strong and extended emission toward the relatively quiescent western core, but only weak and non- extended emission toward the highly active, star-forming, eastern core. We argue that the relative abundance in the eastern core is an order of magnitude lower than that in the western core. Southeast of W 3 Main we detect a new core, which we denote W 3 SE. From our NIR images we detect a jet toward this core. Toward the W 3(OH) cloud, we find an extended ( pc), cold ammonia gas component. We show that the narrow plume of detected toward W 3(OH) in VLA maps, is part of a larger structure extending toward a chain of stellar clusters and nebulosities found in our NIR images. We find that the strong emission detected in the three cores covers 9% of the surveyed region. We estimate virial masses for each core and find that the total sum of the virial masses is 3300 M. The total mass measured from the CO emission surveyed in this region is , thus 20% of the molecular gas in the surveyed region is found in the dense cores. This indicates that the dense cores fill only a small fraction of the total GMC and are concentrated in regions of active star formation. We also find extensive weak emission which covers one fourth of the sur- veyed region. This weak emission may trace gas with densities just sufficient to excite the emission ( cm^-3 ) as well as strongly beam-diluted knots and filaments. We compare in detail the distribution of cores, young stellar clusters, and H II regions, and discuss the effects of star formation on the cores. We also compare the results of our survey to those discussed by Lada (1992) from the CS (2-1) and 2.2µm surveys obtained for the Orion B giant molecular cloud by Lada et al. (1991a, 1991b).

Key words: ISM: W 3; W 3(OH) infrared: ISM: continuum radio lines: ISM ISM: clouds; structure

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observational procedures
  • 2.1. Centimeter observations
  • 2.2. Near-infrared observations
• 3. Results
  • 3.1. The distribution of ammonia cores in the W 3 HDL
  • 3.2. The K'-band mosaic and the identification of stellar clusters
  • 3.3. The morphology of the W 3 main region
  • 3.4. The morphology of the W 3(OH) region
  • 3.5. Determination of kinetic temperature, NH₃ column densities, and virial masses
• 4. Discussion
  • 4.1. The dense gas content of the W 3 GMC
  • 4.2. Star formation and ammonia cores toward W 3
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: July 27, 1998
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