An ALMA study of hub-filament systems – I. On the clump mass concentration within the most massive cores

Abstract

The physical processes behind the transfer of mass from parsec-scale clumps to massive-star-forming cores remain elusive. We investigate the relation between the clump morphology and the mass fraction that ends up in its most massive core (MMC) as a function of infrared brightness, i.e. a clump evolutionary tracer. Using ALMA 12 m and ACA we surveyed 6 infrared-dark hubs in 2.9 mm continuum at ∼3″ resolution. To put our sample into context, we also re-analysed published ALMA data from a sample of 29 high mass-surface density ATLASGAL sources. We characterise the size, mass, morphology, and infrared brightness of the clumps using Herschel and Spitzer data. Within the 6 newly observed hubs, we identify 67 cores, and find that the MMCs have masses between 15–911 M⊙ within a radius of 0.018–0.156 pc. The MMC of each hub contains 3–24 per cent of the clump mass (fMMC), becoming 5–36 per cent once core masses are normalised to the median core radius. Across the 35 clumps, we find no significant difference in the median fMMC values of hub and non-hub systems, likely the consequence of a sample bias. However, we find that fMMC is ∼7.9 times larger for infrared-dark clumps compared to infrared-bright ones. This factor increases up to ∼14.5 when comparing our sample of 6 infrared-dark hubs to infrared-bright clumps. We speculate that hub-filament systems efficiently concentrate mass within their MMC early on during its evolution. As clumps evolve, they grow in mass, but such growth does not lead to the formation of more massive MMCs.

The origin of a universal filament width in molecular clouds

“…The internal structure of molecular clouds is highly filamentary (André et al 2010(André et al , 2014, and the densest filaments appear to play a key role in star formation. Indeed, the majority of low-mass stars appear to form in filaments (Könyves et al 2015(Könyves et al , 2020, and filaments also act to channel material into regions forming high-mass stars (Peretto et al 2013(Peretto et al , 2014Hacar et al 2018;Williams et al 2018;Watkins et al 2019;Anderson et al 2021). Understanding how filaments form and evolve is therefore critical to understanding star formation.…”

Low Mass Stars as Tracers of Star and Cluster Formation

“…Surveys of dense cores with both single-dish telescopes in nearby regions and ALMA in more distant regions will provide an independent means to study star formation rates and efficiencies (e.g. Sokol et al 2019;Anderson et al 2021). This includes using observations of cores to measure the rate of fragmentation or the efficiency of fragmentation per free fall time over the full range of cloud environments (Sec.…”

Formation of the SDC13 Hub-Filament System: A Cloud-Cloud Collision Imprinted on The Multiscale Magnetic Field

“…Statistical analyses based on the clumps identified in the Herschel HiGAL survey show that all massive stars and clusters preferentially form in the density-enhanced centers of HFSs (Kumar et al 2020). Anderson et al (2021) find that infrared dark HFSs tend to concentrate more mass into their largest cores as compared to infrared bright hubs, and they suggest that HFSs can efficiently concentrate mass in the early evolutionary stage. Hence, HFSs are considered a key stage to activate massive star and cluster formation.…”