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Description
To constrain models of high-mass star formation it is important to identify the massive dense cores (MDCs) able to form high-mass star(s). It is one of purposes of the Herschel/HOBYS key program. Here, we make the census and characterisation of the properties of the MDCs population of the NGC 6357 HII region. Our study is based on the Herschel PACS and SPIRE 70-500 microns images of NGC 6357 complemented with (sub)millimetre and mid-infrared data. We followed the procedure, established by the Herschel/HOBYS consortium, to extract ~0.1pc massive dense cores using the getsources software. We estimated their physical parameters (temperatures, masses, luminosities) from spectral energy distribution (SED) fitting. We have obtained a complete census of 23 massive dense cores, amongs which one is found to be IR-quiet and twelve are starless, representing very early stages of the star-formation process. Focussing on the starless MDCs, we consider their evolutionary status, and suggest that only five are likely to form a high-mass star. We find that, contrarily to the case in NGC 6334, the NGC 6357 region does not exhibit any ridge/hub features that are believed to be crucial to the massive star formation process. This study adds support for an empirical model in which massive dense cores and protostars simultaneously accrete mass from the surrounding filaments. In addition, the massive star formation in NGC 6357 seems to have stopped and the hottest stars in Pismis 24 have disrupted the filaments.
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