Linear filament and nested cluster evolution tomography (LANCET)

I. Capture the evolution of dense gas in 14-parsec filament G316.8

¹ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, PR China
² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
³ I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Cologne, Germany
⁴ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia, Michoacán 58089, Mexico
⁵ SRON Netherlands Institute for Space Research & Kapteyn Astronomical Institute, University of Groningen, 9747 AD Groningen, The Netherlands
⁶ Department of Astronomy, University of Florida, 211 Bryant Space Science Center, PO Box 112055, Gainesville, FL 32611-2055, USA
⁷ Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA
⁸ Department of Space, Earth & Environment, Chalmers University of Technology, 412 93 Gothenburg, Sweden
⁹ Department of Physics, National Sun Yat-Sen University, No. 70, Lien-Hai Road, Kaohsiung City 80424, Taiwan, ROC
¹⁰ Center of Astronomy and Gravitation, National Taiwan Normal University, Taipei 116, Taiwan
¹¹ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹² Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
¹³ Departamento de Astronomía, Universidad de Chile, Las Condes, 7591245 Santiago, Chile
¹⁴ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China
¹⁵ Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China

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Received: 30 September 2025
Accepted: 13 February 2026

Abstract

A dynamic view of mass assembly is essential for understanding the formation of massive stars and clusters. However, interpreting evolutionary diagnostics from Galactic-wide surveys requires careful consideration of distance and environmental variations. The G316.8 filament provides an excellent controlled case: a 14-parsec, nearly linear structure comprising three contiguous subregions with comparable molecular gas reservoirs (each ~10 000 M_⊙), yet spanning a clear evolutionary sequence from a northern infrared dark cloud (young) through a central massive young stellar object (intermediate), to a southern HII region (evolved). The Linear filament and nested cluster evolution tomography (LANCET) project mapped the entire G316.8 filament with the Atacama Compact Array (ACA) at 1.3 mm, achieving 6″ (0.08 pc) resolution over 26.7 arcmin² (17.1 pc²). By combining ACA 7 m data with Herschel and APEX/ArTéMiS observations, we produced high-resolution temperature and column-density maps. We quantified subregional differences using (i) dense-fragment statistics, (ii) column-density probability distribution functions (N-PDFs), and (iii) the scale-dependent structural diagnostic, the Δ-variance. From young to intermediate to evolved, the maximum fragment mass increases from 8 to 160 to 490 M_⊙, while the dense-gas mass fraction (>0.5 g cm⁻²) rises from 0.4 to 2.3 to 9.6%. Along this sequence, the N-PDF develops a slightly flatter primary power-law tail and an additional, steeper secondary tail; the Δ-variance slope becomes progressively shallower. Across G316.8, the subregional differences consistently indicate a coherent evolutionary trend of massive star formation, in which gas is continuously assembled into sub-parsec dense structures. The forthcoming 12 m array observations are about to extend this dynamic picture by resolving dense core formation and probing gas kinematics and magnetic fields.