A multiwavelength study of embedded clusters in W5-east, NGC 7538, S235, S252 and S254-S258
Monthly Notices of the Royal Astronomical Society
Oxford University Press on behalf of the Royal Astronomical Society
© 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. This is the final version of the article. Available from OUP via the DOI in this record.
We present Spitzer, near-IR (NIR) and millimetre observations of the massive star-forming regions W5-east, S235, S252, S254-S258 and NGC 7538. Spitzer data is combined with NIR observations to identify and classify the young population while 12CO and 13CO observations are used to examine the parental molecular cloud. We detect in total 3021 young stellar objects (YSOs). Of those, 539 are classified as Class I, and 1186 as Class II sources. YSOs are distributed in groups surrounded by a more scattered population. Class I sources are more hierarchically organized than Class II and associated with the most dense molecular material. We identify in total 41 embedded clusters containing between 52 and 73 per cent of the YSOs. Clusters are in general non-virialized, turbulent and have star formation efficiencies between 5 and 50 per cent. We compare the physical properties of embedded clusters harbouring massive stars (MEC) and low-mass embedded clusters (LEC) and find that both groups follow similar correlations where the MEC are an extrapolation of the LEC. The mean separation between MEC members is smaller compared to the cluster Jeans length than for LEC members. These results are in agreement with a scenario where stars are formed in hierarchically distributed dusty filaments where fragmentation is mainly driven by turbulence for the more massive clusters. We find several young OB-type stars having IR-excess emission which may be due to the presence of an accretion disc.
This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, Caltech, under a contract with NASA. Support for this work was provided by NASA through a contract issued by JPL/Caltech. We also thank NOAO for their student thesis support. The Five College Radio Astronomy Observatory was supported by NSF grant AST 0540852. CB is supported by an RCUK Fellowship at the University of Exeter, UK. This work is based in part on the IRAC postBCD processing software ‘IRACPROC’ developed by Mike Schuster, Massimo Marengo and Brian Patten at the Smithsonian Astrophysical Observatory. This research used the facilities of the Canadian Astronomy Data Centre operated by the National Research Council of Canada with the support of the Canadian Space Agency. This research has made use of the NASA/ IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We thank the Spanish MINECO for funding support from grants CSD2009-00038, AYA2009-07304 and AYA2012-32032.
Vol. 439, No. 4, pp. 3719-3754