The ALMA-QUARKS Survey: Discovery of Dusty Fibrils inside Massive Star-forming Clumps

TL;DR

This study leverages the high-resolution ALMA-QUARKS 1.3 mm continuum data to uncover a large population of superfine dusty fibrils within 121 massive star-forming clumps across a wide Galactic range. By applying FilFinder and RadFil, the authors quantify fibril widths (~0.01 pc), masses (up to ~4424 M_⊙), and a mass–length relation $M \propto L^{2}$, revealing densities far higher than those of previously identified filaments. They demonstrate that these fibrils are distinctively short and dense compared to Herschel filaments and discuss their potential formation mechanisms, including shock compression and lateral gravitational contraction, as well as their possible role in funneling material to central high-mass protostars. The results suggest fibrils are a widespread, gravitationally significant filamentary component in high-mass star formation, meriting further investigation into their dynamics, chemistry, and impact on protostellar accretion processes.

Abstract

We report the discovery of more than 323 superfine dusty filamentary structures (fibrils) inside 121 massive star forming clumps that are located in widely different Galactic environments (Galactocentric distances of $\sim$0.5-12.7 kpc). These fibrils are identified from the 1.3~mm continuum emission in the ALMA-QUARKS survey, which has a linear resolution of $\sim900$ AU for a source at $\sim$3 kpc, using the \textit{FilFinder} software. Using \textit{RadFil} software, we find that the typical width of these fibrils is $\sim$0.01 pc, which is about ten times narrower than that of dusty filaments in nearby clouds identified by the \textit{Herschel} Space Observatory. The mass ($M$) versus length ($L$) relation for these fibrils follows $M\propto L^{2}$, similar to that of Galactic filaments identified in space (e.g., \textit{Herschel}) and ground-based single-dish (e.g., \textit{APEX}) surveys. However, these fibrils are significantly denser ($\mathrm{N_{H_2} = 10^{23}-10^{24}\ cm^{-2}}$) than the filaments found in previous \textit{Herschel} surveys ($\mathrm{N_{H_2} = 10^{20}-10^{23}\ cm^{-2}}$). This work contributes a large sample of superfine fibrils in massive clumps, following the identification of large 0.1-pc wide filaments and associated internal velocity coherent fibers in nearby molecular clouds, further emphasizing the crucial role played by filamentary structures in star formation at various physical scales.

Figures (6)

• Figure 1: Multi-wavelength picture of the exemplar source I12320-6122. Left Panel: Spitzer three-color composite (blue: 3.6-$\micron$; green: 4.5-$\micron$, red: 8.0-$\micron$) image overlaid with the ATLASGAL 870-$\micron$ data shown by white contours and the MeerKAT Galactic Plane Survey (MGPS) 1.28-GHz data shown by yellow contours (see also in 2024RAA....24f5011X). The field of view (FoV) of the combined ATOMS (12-m + ACA) 3-mm continuum data ($\sim$80$^{\prime\prime}$) and the QUARKS (12-m C2 & C5 + ACA) 1.3-mm data ($\sim$40$^{\prime\prime}$) is shown by the red and cyan circles, respectively. The atlas for all sources are shown in a companion work (Jiao W.-Y., et al. 2026, in preparation). Right Panel: the 1.3-mm continuum emission, for the same region, as detected from the QUARKS survey is shown as the background with fibrils appearing as red structures according to the intensity scale on the right. The spines of fibrils are shown with sky-blue curves, the branches are shown with gray curves, and the purple circles mark locations of cores or condensations identified by using getsf (Jiao W.-Y. et al. 2026, in preparation). For the lime-green contours representing the H40$\alpha$ line emission detected in the ATOMS survey, the start, step and end levels are 0.025, 1.520 and 13.500 Jy beam$^{-1}$ km s$^{-1}$, respectively.
• Figure 2: Left panel: The grey background shows one of the fibrils identified in the I12320-6122. The blue points mark the location of the peak sampling points along the fibril in RadFil, while the thick red curve represent the sampling path that is rouphly consistent with the sampling points. The thin red lines that are perpendicular to the thick curve and across the points are the paths where the profile data were extracted. Right Panel: The black points outline the profiles along the different lines perpendicular to the spine of the main fibril (i.e., the thin red lines). In the upper panel, the shaded green areas show the regions where the data are used for extracting the baseline that is indicated by the thick green line. In the middle panel, the shaded blue area and curve show the data used for obtaining the parameters of the Plummer profile and fitting line. The magenta and cyan dashed lines are the averaged mean and median curves, respectively. The meaning of the shaded blue area, blue line, the dashed magenta and cyan lines in the lower panel are the same as that in the middle panel, but for fitting the Gaussian profile.
• Figure 3: Left Panel: a histogram of the FWHM in the Plummer profile fitting for prominent fibrils identified by using FilFinder. The pink (red), yellow (green) and skyblue (blue) bins (curves) are the Kernel Density Estimation (KDE) curves for fibrils within sources containing H II regions, without H II regions traced by H40$\alpha$ emission, and for the whole sample, respectively. The dashed blue line marks the location where the blue curve peaks. Right Panel: the same as the figure shown in the left panel, but for statistical results from the Gaussian profile fittings.
• Figure 4: Mass-Length relations among the H I filamentary clouds (2014ApJ...789...82C2023ASPC..534..153H2026AJ....171...76P), the dusty filaments detected in the Hi-Gal project (2020MNRAS.492.5420S), and the superfine fibrils detected in the QUARKS survey. The colored and open contours are used to present the Mass-Length distributions of the H I clouds and the dusty filaments, respectively. The fitting results of their distributions are shown by the solid and sky-blue lines, correspondingly. The non-circled red and green crosses represent the common filaments and giant filaments detected in the ATLASGAL survey (2016AA...591A...5L), respectively. In addition, the blue squares represent the hub-filament systems compiled in 2025AA...694A..69H. For the QUARKS sample, we use dotted red and green lines to indicate the fitted Mass-Length relation of superfine fibrils within clumps/protoclusters that correspondingly are and are not found to emit H40$\alpha$ line emission, while the solid blue line are used to indicate the overall Mass-Length relation of superfine fibrils.
• Figure 5: Panel (a) presents the numerical simulation result for the L1495 cloud. The colored background presents the column density distribution of the H$_2$. The gray curve marks the typical filamentary structure that is used for checking the physical reality of fibrils. Panel (b) presents the identification result of the fibril marked by the grey curve in panel (a), where the meaning of red curve/segments or blue points are the same as that shown in Figure \ref{['fig:FittingWidth']}. Panel (c) presents the Plummer and Gaussian fittings in RadFil for the (column) density profile of the fibril marked in panels (a) and (b). The meaning of the curves and datapoints are the same as that shown in Figure \ref{['fig:FittingWidth']}.