| 1. |
- Barnes, Ashley T., et al.
(författare)
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Young massive star cluster formation in the Galactic Centre is driven by global gravitational collapse of high-mass molecular clouds
- 2019
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 486:1, s. 283-303
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Tidskriftsartikel (refereegranskat)abstract
- Young massive clusters (YMCs) are the most compact, high-mass stellar systems still forming at the present day. The precursor clouds to such systems are, however, rare due to their large initial gas mass reservoirs and rapid dispersal time-scales due to stellar feedback. None the less, unlike their high-z counterparts, these precursors are resolvable down to the sites of individually forming stars, and hence represent the ideal environments in which to test the current theories of star and cluster formation. Using high angular resolution (1 arcsec / 0.05 pc) and sensitivity ALMA observations of two YMC progenitor clouds in the Galactic Centre, we have identified a suite of molecular line transitions - e.g. c-C3H2 (7 - 6) - that are believed to be optically thin, and reliably trace the gas structure in the highest density gas on star-forming core scales. We conduct a virial analysis of the identified core and proto-cluster regions, and show that half of the cores (5/10) and both proto-clusters are unstable to gravitational collapse. This is the first kinematic evidence of global gravitational collapse in YMC precursor clouds at such an early evolutionary stage. The implications are that if these clouds are to form YMCs, then they likely do so via the 'conveyor-belt' mode, whereby stars continually form within dispersed dense gas cores as the cloud undergoes global gravitational collapse. The concurrent contraction of both the cluster-scale gas and embedded (proto-)stars ultimately leads to the high (proto-)stellar density in YMCs.
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| 2. |
- Cosentino, Giuliana, et al.
(författare)
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Interstellar Plunging Waves: ALMA Resolves the Physical Structure of Nonstationary MHD Shocks
- 2019
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 881:2
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Tidskriftsartikel (refereegranskat)abstract
- Magnetohydrodynamic (MHD) shocks are violent events that inject large amounts of energy in the interstellar medium dramatically modifying its physical properties and chemical composition. Indirect evidence for the presence of such shocks has been reported from the especial chemistry detected toward a variety of astrophysical shocked environments. However, the internal physical structure of these shocks remains unresolved since their expected spatial scales are too small to be measured with current instrumentation. Here we report the first detection of a fully spatially resolved, MHD shock toward the infrared dark cloud (IRDC) G034.77-00.55. The shock, probed by silicon monoxide (SiO) and observed with the Atacama Large Millimeter/submillimeter Array (ALMA), is associated with the collision between the dense molecular gas of the cloud and a molecular gas flow pushed toward the IRDC by the nearby supernova remnant (SNR) W44. The interaction is occurring on subparsec spatial scales thanks to the enhanced magnetic field of the SNR, making the dissipation region of the MHD shock large enough to be resolved with ALMA. Our observations suggest that molecular flow-flow collisions can be triggered by stellar feedback, inducing shocked molecular gas densities compatible with those required for massive star formation.
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