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

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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 6

1 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


We simultaneously mapped the metastable (J,K) = (1,1) and (2,2) inversion lines of [FORMULA] toward W 3 Main, W 3(OH), and the region between these two star-forming clouds with a [FORMULA] angular resolution using the 100-m Effelsberg telescope. We observed a 120 square-arcminute region with [FORMULA] spacing and a significantly higher sensitivity than previous maps. We also measured the (J,K) = (3,3) line of [FORMULA] in 28 positions toward W 3 Main. For comparison with our [FORMULA] survey, we present a [FORMULA]-band (2.1 µm) survey conducted by J. T. Rayner. The [FORMULA]-band survey detects five distinct stellar clusters within the mapped region. In addition, we compare the [FORMULA] 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 [FORMULA] for regions of strong [FORMULA] emission, d) compare the distribution of the [FORMULA] 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 [FORMULA] 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 [FORMULA] 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 [FORMULA] 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 ([FORMULA] pc), cold ammonia gas component. We show that the narrow plume of [FORMULA] detected toward W 3(OH) in VLA maps, is part of a larger [FORMULA] structure extending toward a chain of stellar clusters and nebulosities found in our NIR images. We find that the strong [FORMULA] emission detected in the three cores covers 9% of the surveyed region. We estimate virial masses for each [FORMULA] core and find that the total sum of the virial masses is 3300 M[FORMULA]. The total mass measured from the CO emission surveyed in this region is [FORMULA] [FORMULA], 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 [FORMULA] emission which covers one fourth of the sur- veyed region. This weak emission may trace gas with densities just sufficient to excite the [FORMULA] emission ([FORMULA] cm-3 ) as well as strongly beam-diluted knots and filaments. We compare in detail the distribution of [FORMULA] cores, young stellar clusters, and H II regions, and discuss the effects of star formation on the [FORMULA] 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

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© European Southern Observatory (ESO) 1998

Online publication: July 27, 1998