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

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

Aug 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998a%26a...336..991t&link_type=abstract

Astronomy and Astrophysics, v.336, p.991-1006 (1998)

Astronomy and Astrophysics

Astrophysics

36

Ism: W 3, W 3(Oh), Infrared: Ism: Continuum, Radio Lines: Ism, Ism: Clouds, Structure

Scientific paper

We simultaneously mapped the metastable (J,K) = (1,1) and (2,2) inversion lines of NH3 toward W 3 Main, W 3(OH), and the region between these two star-forming clouds with a 40('') angular resolution using the 100-m Effelsberg telescope. We observed a 120 square-arcminute region with 20('') spacing and a significantly higher sensitivity than previous maps. We also measured the (J,K) (3,3) line of NH3 in 28 positions toward W 3 Main. For comparison with our NH3 survey, we present a K'-band (2.1 {^m}um) survey conducted by J. T. Rayner. The K'-band survey detects five distinct stellar clusters within the mapped region. In addition, we compare the NH3 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 T_kin for regions of strong NH3 emission, d) compare the distribution of the NH3 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 NH3 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 NH3 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 NH3 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 (2 x 1.3 pc), cold ammonia gas component. We show that the narrow plume of NH3(1,1), detected toward W 3(OH) in VLA maps, is part of a larger NH3 structure extending toward a chain of stellar clusters and nebulosities found in our NIR images. We find that the strong NH3 emission detected in the three cores covers 9% of the surveyed region. We estimate virial masses for each NH3 core and find that the total sum of the virial masses is 3300 Msun. The total mass measured from the CO emission surveyed in this region is 1.6 x 10(4) {^h}{M}_sun, 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 NH3 emission which covers one fourth of the surveyed region. This weak emission may trace gas with densities just sufficient to excite the NH3 emission (10(4) {^h}box{cm}(-3) ) as well as strongly beam-diluted knots and filaments. We compare in detail the distribution of NH3 cores, young stellar clusters, and H ii regions, and discuss the effects of star formation on the NH3 cores. We also compare the results of our survey to those discussed by Lada (1992) from the CS (2-1) and 2.2 {^m}um surveys obtained for the Orion B giant molecular cloud by Lada et al. (1991a,1991b).

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