NARIT News
FIRESTORM I (MNRAS accepted):
Stellar feedback and gas kinematics
in the evolved W40 hub–filament system
Astronomers from the National Astronomical Research Institute of Thailand (NARIT) and international collaborators have carried out a new multi-wavelength study of W40, a nearby high-mass star-forming region shaped by the intense radiation and winds from young massive stars. The paper, accepted for publication in the Monthly Notices of the Royal Astronomical Society (MNRAS), presents a detailed view of the dense gas “skeleton” of W40-revealing how gas is organized into filaments, how it flows, and how stellar feedback is stirring and dispersing the cloud.
Figure 1: W40 shown in three colours: Herschel 250 μm (red; cold dust), Spitzer 8 μm (green; warm dust/PAHs),
and Hα (blue; ionized gas). The central massive star is marked, and the white box indicates
the area mapped with the TRAO 14-m telescope.
W40 hosts a prominent bipolar H II region (a bubble of ionized gas) powered mainly by the massive star IRS 1A South (O9.5V). Because W40 is both nearby and evolved, it is an excellent target to investigate a central question in star formation research: how massive stars assemble their mass from dense gas, and how their feedback later reshapes the same material.
This work is part of FIRESTORM (Feedback-Induced Regions and Emission from Star-forming Tracers of ObseRvable Molecular Gas), a program designed to quantify how feedback from massive stars affects dense gas and star formation. The team used new TRAO 14-m radio observations of multiple molecular lines—together with archival data from Nobeyama 45-m, IRAM 30-m, and the James Clerk Maxwell Telescope (JCMT) 15-m—to connect cloud structure and gas motion across a wide range of densities.
Main findings
1) A hub fed by multiple filaments
The analysis identified six velocity-coherent filaments in W40. Importantly, four filaments converge toward the central infrared-bright cluster hosting IRS 1A South, forming a classic hub–filament system. In simple terms, W40 contains several dense gas “streams” that meet in a central hub where massive stars and clusters form.
Figure 2: Six velocity-coherent filaments identified in the W40 cloud.
Colours represent the gas velocity along each filament.
2) Dense clumps: compact sites where stars can form
Within these filaments, the team detected five dense clumps traced by N₂H⁺ emission. These clumps represent compact, locally denser regions—prime candidates for current or future star formation. The clumps show subsonic to transonic internal motions, while their larger parent filaments are supersonic, indicating that turbulence can dissipate as gas condenses to smaller scales.
Figure 3: Dense-gas clumps traced by N₂H⁺ emission, overlaid with young stellar cores
(starless, prestellar, protostellar) and contours highlighting the central ionized gas distribution.
3) Signatures of stellar feedback
The study finds that non-thermal motions (turbulence) increase in filaments located closer to the H II region. This provides direct evidence that feedback from massive stars is stirring and reshaping the surrounding dense gas, especially in regions nearest to the bubble.
4) Clues to W40’s earlier history: a likely interaction between clouds
Several molecular lines show a deficit of emission near ~7 km/s and a blueshifted absorption feature in HCN, consistent with cold foreground gas absorbing emission from warmer, OB-heated gas. In addition, a bridge-like feature in position–velocity space connects two main velocity components (~5 and ~7.5 km/s) and coincides with dense condensations and radio continuum peaks. Together, these signatures support a scenario in which a past interaction—likely a cloud–cloud collision—helped assemble the hub and form the central massive cluster, followed by feedback-driven dispersal of the parental gas.
Massive stars are rare but disproportionately important: they shape galaxies by injecting energy and momentum into the interstellar medium. Studies like this one help link the earliest “assembly phase” (gas converging into hubs through filaments and interactions) to the later feedback-dominated phase, when ionized bubbles, winds, and radiation begin to disperse and rearrange the cloud.
References: Ming-Kang Lim, Ram K. Yadav et al., “FIRESTORM I: Stellar Feedback and Gas Kinematics in the Evolved W40 Hub-Filament”, Accepted in Monthly Notices of the Royal Astronomical Society (MNRAS)
https://arxiv.org/abs/2512.08811;
https://academic.oup.com/mnras/advance-article-abstract/doi/10.1093/mnras/staf2218/8380060?utm_source=authortollfreelink&utm_campaign=mnras&utm_medium=email
Contact: [email protected] (Ming-Kang Lim); [email protected] (Ram K. Yadav)