Abstract
Aims. To constrain the physical processes that lead to the birth of high-mass stars it is mandatory to study the very first stages of their formation. We search for high-mass analogs of low-mass prestellar cores in W43-MM1. Methods. We conducted a 1.3 mm ALMA mosaic of the complete W43-MM1 cloud, which has revealed numerous cores with ~2000 au FWHM sizes. We investigated the nature of cores located at the tip of the main filament, where the clustering is minimum. We used the continuum emission to measure the core masses and the 13CS(5-4) line emission to estimate their turbulence level. We also investigated the prestellar or protostellar nature of these cores by searching for outflow signatures traced by CO(2-1) and SiO(5-4) line emission, and for molecular complexity typical of embedded hot cores. Results. Two high-mass cores of ~1300 au diameter and ~60 M⊙ mass are observed to be turbulent but gravitationally bound. One drives outflows and is associated with a hot core. The other core, W43-MM1#6, does not yet reveal any star formation activity and thus is an excellent high-mass prestellar core candidate.
Highlights
Despite the large efforts made in the past ten years to improve our understanding of the formation of high-mass stars, two competing families of models remain
We investigated the prestellar or protostellar nature of these cores by searching for outflow signatures traced by CO(2-1) and SiO(5-4) line emission, and for molecular complexity typical of embedded hot cores
In the empirical evolutionary sequence recently proposed for the formation of high-mass stars, the highmass prestellar core phase does not even exist and high-mass protostellar cores form from low-mass protostellar cores, which accrete further material from their parental massive dense core (MDC; Motte et al 2018a)
Summary
Despite the large efforts made in the past ten years to improve our understanding of the formation of high-mass stars, two competing families of models remain. In the “core-fed” or “coreaccretion” models, a high-mass star forms through the monolithic collapse of a massive, turbulent prestellar core that formed quasi-statically (e.g., McKee & Tan 2003). The “clump-fed” models involve the gas mass reservoir surrounding individual cores through dynamical processes in their parental cloud. W43, located at 5.5 kpc from the Sun (Zhang et al 2014), contains two of the largest groups of molecular clouds in the first Galactic quadrant, among them W43-MM1 (Nguyen Luong et al 2011, 2013) This 6 pc ridge has a 2 × 104 M mass and qualifies as “mini-starburst” because its star formation activity is reminiscent of that of starburst galaxies (SFR ∼ 6000 M Myr−1; Motte et al 2003; Louvet et al 2014).
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