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Paper: High-Mass Stars as an Early Signpost of Cluster Formation
Volume: 267, Hot Star Workshop III: the Earliest Stages of Massive Star Birth
Page: 247
Authors: Tieftrunk, A. R.; Thorwirth, S.; Megeath, S. T.
Abstract: The connection between high-mass stars and young stellar clusters has been well established by near-IR observations showing young massive stars in HII regions surrounded by clusters of lower mass stars. Millimeter-wave observations show that these clusters form in approx 1000 Msun dense cores. Interestingly, the mm-wave observations of very active cluster-forming regions also reveal the presence of seemingly quiescent dense massive cores, which contain few signs of ongoing star formation. In the W3 Main region, next to the cluster-forming cores W3 SMS1 &2, we find a approx 1000 Msun mass dense core which contains no mid-IR or cm-continuum sources. Near-IR imaging of this core has failed to detect any embedded sources. Yet, we suggest that this region is at an early stage of cluster formation. This is given support by comparative observations of a similar twin core system in the NGC 6334 GMC. Here, north of the highly active star-forming core NGC 6334 I, we find another quiescent massive approx 1000 Msun core without mid-IR sources, HII regions, or a detectable near-IR cluster. Motivated by the presence of CH3OH and H2O masers in this IR-quiet core, we have searched for and detected a bipolar outflow driven by a young massive star deeply embedded in the core. The presence of an embedded high-mass star strengthens our arguments that IR-quiet cores are at an early stage of cluster formation. We propose that masers and outflows from very deeply embedded (and consequently IR-quiet) high-mass stars are among the first incipient signposts of cluster formation in massive cores. Accordingly, we have undertaken a SEST survey of 46 CH3OH maser clusters from the survey of Walsh et al. which are not coincident with IRAS sources or HII regions. From this sample, we detected outflows in transitions of SiO toward 15 of the maser clusters. These sources have now been observed at 1200micron with SIMBA, the 37-multichannel bolometer at SEST.
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