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Abstract: Recent 1.2-mm continuum observations have shown the giant HII region NGC3576to be embedded in the centre of an extended filamentary dust-cloud. The bulk ofthe filament away from the HII region contains a number of clumps seen only atsub-millimetre wavelengths and which may host massive protostellar objects ata very early stage of evolution. We have used the Australia Telescope CompactArray ATCA to image the cloud for the NH31,1, 2,2 and 4,4 transitions,22 GHz water masers, and 23 GHz continuum emission. We also utilised the 22-mMopra antenna to map the region for the molecular lines 13CO 1-0, C18O 1-0,HCO+ 1-0, H13CO+ 1-0, CS 1-0 and N2H+ 1-0.The HII region is observed tobe expanding into the molecular cloud, sweeping up a clumpy shell of gas, whilethe central star cluster is dispersing the molecular gas to the east.Temperatures are highest adjacent to the central HII region, indicating thatthe embedded cluster of young stars there is heating the gas. Six new watermasers were detected in the arms of the filament, all associated with NH3emission peaks, confirming that star-formation has begun within these cores.Core masses range from 5 to 516 solar masses and most appear to begravitationally bound. Complementary results by Andr\-e et al. 2008 implythat seven cores will go on to form massive stars between 15 and 50 solarmasses. The large scale velocity structure of the filament is smooth, but atleast one clump shows the signature of inward gas motions via asymmetries inthe NH3 1,1 line profiles. The same clump exhibits an enhanced abundance ofN2H+, which coupled with an absence of CO indicates depletion onto the dustgrain surface. The HII region at the heart of NGC3576 is potentially triggeringthe formation of massive stars in the bulk of the associated cloud.



Author: C. R. Purcell, V. Minier, S. N. Longmore, Ph. André, A. J. Walsh, P.Jones, F. Herpin, T. Hill, M. R. Cunningham, M. G. Burton

Source: https://arxiv.org/



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