Mon. Not. R. Astron. Soc., 491, 4573-4589 (2020/January-3)
Super Hot Cores in NGC 253: witnessing the formation and early evolution of super star clusters.
RICO-VILLAS F., MARTIN-PINTADO J., GONZALEZ-ALFONSO E., MARTIN S. and RIVILLA V.M.
Abstract (from CDS):
Using 0.2 arcsec (∼3 pc) ALMA images of vibrationally excited HC3N emission (HC3N*) we reveal the presence of eight unresolved Super Hot Cores (SHCs) in the inner 160 pc of NGC 253. Our LTE and non-LTE modelling of the HC3N* emission indicate that SHCs have dust temperatures of 200-375 K, relatively high H2 densities of (1-6) x 106 cm-3 and high IR luminosities of (0.1-1) x 108 L☉. As expected from their short-lived phase (∼104 yr), all SHCs are associated with young super star clusters (SSCs). We use the ratio of luminosities from the SHCs (protostar phase) and from the free-free emission (ZAMS star phase), to establish the evolutionary stage of the SSCs. The youngest SSCs, with the larges ratios, have ages of a few 104 yr (proto-SSCs) and the more evolved SSCs are likely between 105 and 106 yr (ZAMS-SSCs). The different evolutionary stages of the SSCs are also supported by the radiative feedback from the UV radiation as traced by the HNCO/CS ratio, with this ratio being systematically higher in the young proto-SSCs than in the older ZAMS-SSCs. We also estimate the SFR and the SFE of the SSCs. The trend found in the estimated SFE ( 40 per cent for proto-SSCs and > 85 per cent for ZAMS-SSCs) and in the gas mass reservoir available for star formation, one order of magnitude higher for proto-SSCs, suggests that star formation is still going on in proto-SSCs. We also find that the most evolved SSCs are located, in projection, closer to the centre of the galaxy than the younger proto-SSCs, indicating an inside-out SSC formation scenario.
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
galaxies: individual: NGC 253 - galaxies: ISM - galaxies: nuclei - galaxies: star clusters: general - galaxies: star formation
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