Fragmentation and filaments at the onset of star and cluster formation

Abstract

Context. The structure formation of the dense interstellar material and the fragmentation of clumps into cores is a fundamental step to understand how stars and stellar clusters form. Aims. We aim to establish a statistical view of clump fragmentation at sub-parsec scales based on a large sample of massive clumps selected from the ATLASGAL survey. Methods. We used the APEX/SABOCA camera at 350 µm to image clumps at a resolution of 8. 5, corresponding to physical scales of <0.2 pc at a distance <5 kpc. The majority of the sample consists of massive clumps that are weak or in absorption at 24 µm. We resolve spherical and filamentary structures and identify the population of compact sources. Complemented with archival Herschel data, we derive the physical properties, such as dust temperature, mass and bolometric luminosity of clumps and cores. We use association with mid-infrared 22-24 µm and 70 µm point sources to pin down the star formation activity of the cores. We then statistically assess their physical properties, and the fragmentation characteristics of massive clumps. Results. We detect emission at 350 µm towards all targets and find that it typically exhibits a filamentary(-like) morphology and hosts a population of compact sources. Using Gaussclumps we identify 1120 compact sources and derive the physical parameters and star formation activity for 971 of these, 874 of which are associated with 444 clumps. We find a moderate correlation between the clump fragmentation levels with the clump gas density and the predicted number of fragments with pure Jeans fragmentation scenario. We find a strong correlation between the mass of the most massive fragment and the total clump mass, suggesting that the self-gravity may play an important role in the clumps' small scale structure formation. Finally, due to the improved angular resolution compared to ATLASGAL, we are able to identify 27 massive quiescent cores with M core > 100 M within 5 kpc; these are massive enough to be self-gravitating but do not yet show any sign of star-formation. This sample comprises, therefore, promising candidates of massive pre-stellar cores, or deeply embedded high-mass protostars. Conclusions. The submillimeter observations of the massive clumps that are weak or completely dark at 24 µm reveal rich filamentary structures and an embedded population of compact cores. The maximum core mass is likely determined by the self-gravity of the clump. The rarity of massive pre-stellar core candidates implies short collapse time-scales for dense structures.

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

“…A tight correlation between clump mass and mass of the MMC was found by Lin et al (2019) for a sample of ATLASGAL clumps covering a large range of evolutionary stages as traced by their luminosity to mass ratio. This is at odds with the results discussed above for the full sample.…”

“…This is at odds with the results discussed above for the full sample. It is likely that the tight correlation observed by Lin et al (2019) is artificially driven by the small range of scales they probe, typically 0.3 pc for what they call cores and 0.7 pc for their clumps (a factor of ∼2.3). In our study, the range of scales we probe between the median core size (0.08 pc) and the median clump size (1.5 pc) is a lot larger, a factor of ∼18.8, therefore probing clearly distinct structures.…”

“…They also find a correlation between the cloud mass and the mass of its most massive core (MMC). The existence of such a relation has also been explored by Lin et al (2019), who found a tight correlation between the mass of a subsample of massive ATLASGAL clumps and the mass of the most massive fragment they identify on SABOCA 350 μm continuum images. However, the small difference in angular resolution between LABOCA (18 arcsec) and SABOCA (8.5 arcsec) might play a significant part in driving the observed correlation.…”

The evolution of temperature and density structures of OB cluster-forming molecular clumps

“…In addition to the 870 µm data from ATLASGAL survey (Schuller et al 2009;Csengeri et al 2016) obtained by APEX-LABOCA (Siringo et al 2009), we also adopted 350 µm data obtained by the CSO-SHARC2 or APEX-SABOCA instrument. The information of the observations and data reduction procedure are detailed in Lin et al (2017) and Lin et al (2019). For sources without available 350 µm from ground-based telescope (of 10 angular resolution), we used ρ(r) for bulk gas, ρ bulk (r) (Table 6) LIME modeling of CH 3 OH and CH 3 CCH with T (r) and ρ(r) fixed, ρ(r) = ρ bulk (r) (Appendix F) Best-fit model cube and abundance profiles (Table 7) n(H ) map (Fig.…”

ATLASGAL – evolutionary trends in high-mass star formation

“…The ATLASGAL CSC has therefore been the focus of an intensive campaign to characterise the properties and evolutionary state of the clumps. These have included dedicated molecular-line studies to produce the kinematics, temperatures, chemistry and determine kinematic distances (Wienen et al 2012;Giannetti et al 2014;Wienen et al 2015;Csengeri et al 2016;Kim et al 2017Kim et al , 2018Wienen et al 2018;Tang et al 2018;Navarete et al 2019;Urquhart et al 2019) and detailed analysis of clumps associated with star-formation tracers such as HII regions (Urquhart et al 2013b), methanol masers (Urquhart et al 2013a(Urquhart et al , 2015Billington et al 2019Billington et al , 2020, massive young stellar objects (MYSO; Urquhart et al 2014b;König et al 2017;Urquhart et al 2018) and filamentary structures (Li et al 2016;Mattern et al 2018;Lin et al 2019). This programme of follow-up observations and use of complementary multi-wavelength studies has resulted in the ATLASGAL sample being the most well characterised sample of high-mass star-forming clumps currently available.…”