Highly structured turbulence in high-mass star formation: An evolved infrared-dark cloud G35.20-0.74 N

Wang, K. Wang C.

doi:10.1051/0004-6361/202244525

A&A

2023

DOI: 10.1051/0004-6361/202244525

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Highly structured turbulence in high-mass star formation: An evolved infrared-dark cloud G35.20-0.74 N

K. Wang C. Wang¹

Abstract: Context. Massive stars are generally believed to form in supersonic turbulent environment. However, recent observations have challenged this traditional view. High spatial and spectral resolution observations of the Orion Molecular Cloud (OMC, the closest massive star formation region) and an infrared dark cloud (IRDC) G35.39 (a typical distant massive star formation region) show a resolutiondependent turbulence, and that high-mass stars are forming exclusively in subsonic to transonic cores in those clouds. T… Show more

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2024

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The role of turbulence in high-mass star formation: Subsonic and transonic turbulence are ubiquitously found at early stages

Wang,

et al. 2024

A&A

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Context. Traditionally, supersonic turbulence is considered to be one of the most likely mechanisms slowing the gravitational collapse in dense clumps, thereby enabling the formation of massive stars. However, several recent studies have raised differing points of view based on observations carried out with sufficiently high spatial and spectral resolution. These studies call for a re-evaluation of the role turbulence plays in massive star-forming regions. Aims. Our aim is to study the gas properties, especially the turbulence, in a sample of massive star-forming regions with sufficient spatial and spectral resolution, which can both resolve the core fragmentation and the thermal line width. Methods. We observed NH3 metastable lines with the Very Large Array (VLA) to assess the intrinsic turbulence. Results. Analysis of the turbulence distribution histogram for 32 identified NH3 cores reveals the presence of three distinct components. Furthermore, our results suggest that (1) sub- and transonic turbulence is a prevalent (21 of 32) feature of massive star-forming regions and those cold regions are at early evolutionary stage. This investigation indicates that turbulence alone is insufficient to provide the necessary internal pressure required for massive star formation, necessitating further exploration of alternative candidates; and (2) studies of seven multi-core systems indicate that the cores within each system mainly share similar gas properties and masses. However, two of the systems are characterized by the presence of exceptionally cold and dense cores that are situated at the spatial center of each system. Our findings support the hub-filament model as an explanation for this observed distribution.

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The role of turbulence in high-mass star formation: Subsonic and transonic turbulence are ubiquitously found at early stages

Wang,

et al. 2024

A&A

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Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde

Zhao,

Tang,

Henkel

et al. 2024

A&A

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The kinetic temperature structure of the massive filament DR21 within the Cygnus X molecular cloud complex has been mapped using the IRAM\,30\,m telescope. This mapping employed the para-H$_2$CO triplet K_aK_c $, and 3$_ $) on a scale of sim 0.1\,pc. By modeling the averaged line ratios of $ and 3$_ $ with RADEX under non local thermodynamic equilibrium (LTE) assumptions, the kinetic temperature of the dense gas was derived, which ranges from 24 to 114\,K, with an average temperature of 48.3\,pm \,0.5\,K at a density of $. In comparison to temperature measurements using NH$_3$\,(1,1)/(2,2) and far-infrared (FIR) wavelengths, the para-H$_2$CO\,(3--2) lines reveal significantly higher temperatures. The dense clumps in various regions appear to correlate with the notable kinetic temperature kin $\,gtrsim \,50\,K) of the dense gas traced by H$_2$CO. Conversely, the outskirts of the DR21 filament display lower temperature distributions kin $\,$<$\,50\,K). Among the four dense cores (N44, N46, N48, and N54), temperature gradients are observed on a scale of sim 0.1-0.3\,pc. This suggests that the warm dense gas traced by H$_2$CO is influenced by internal star formation activity. With the exception of the dense core N54, the temperature profiles of these cores were fitted with power-law indices ranging from $-$0.3 to $-$0.5, with a mean value of approximately $-$0.4. This indicates that the warm dense gas probed by H$_2$CO is heated by radiation emitted from internally embedded protostar(s) and/or clusters. While there is no direct evidence supporting the idea that the dense gas is heated by shocks resulting from a past explosive event in the DR21 region on a scale of sim 0.1\,pc, our measurements of H$_2$CO toward the DR21W1 region provide compelling evidence that the dense gas in this specific area is indeed heated by shocks originating from the western DR21 flow. Higher temperatures as traced by H$_2$CO appear to be associated with turbulence on a scale of sim 0.1\,pc. The physical parameters of the dense gas as determined from H$_2$CO lines in the DR21 filament exhibit a remarkable similarity to the results obtained in OMC-1 and N113, albeit on a scale of approximately 0.1-0.4\,pc. This may imply that the physical mechanisms governing the dynamics and thermodynamics of dense gas traced by $CO in diverse star formation regions may be dominated by common underlying principles despite variations in specific environmental conditions.

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Massive Star Formation Starts in Subvirial Dense Clumps Unless Resisted by Strong Magnetic Fields

Wang,

2024

ApJL

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Knowledge of the initial conditions of high-mass star formation is critical for theoretical models, but are not well observed. Built on our previous characterization of a Galaxy-wide sample of 463 candidate high-mass starless clumps (HMSCs), here we investigate the dynamical state of a representative subsample of 44 HMSCs (radii 0.13–1.12 pc) using Green Bank Telescope NH3 (1,1) and (2,2) data from the Radio Ammonia Mid-Plane Survey pilot data release. By fitting the two NH3 lines simultaneously, we obtain velocity dispersion, gas kinetic temperature, NH3 column density and abundance, Mach number, and virial parameter. Thermodynamic analysis reveals that most HMSCs have Mach number <5, inconsistent with what have been considered in theoretical models. All but one (43 out of 44) of the HMSCs are gravitationally bound with virial parameter α vir < 2. Either these massive clumps are collapsing or magnetic field strengths of 0.10–2.65 mG (average 0.51 mG) would be needed to prevent them from collapsing. The estimated B-field strength correlates tightly with density, B est / mG = 0.269 ( n H 2 / 10 4 cm − 3 ) 0.61 , with a similar power-law index as found in observations but a factor of 4.6 higher in strength. For the first time, the initial dynamical state of high-mass formation regions has been statistically constrained to be subvirial, in contradiction to theoretical models in virial equilibrium and in agreement with the lack of observed massive starless cores. The findings urge future observations to quantify the magnetic field support in the prestellar stage of massive clumps, which has rarely been explored so far, toward a full understanding of the physical conditions that initiate massive star formation.

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Highly structured turbulence in high-mass star formation: An evolved infrared-dark cloud G35.20-0.74 N

Cited by 3 publications

References 53 publications

The role of turbulence in high-mass star formation: Subsonic and transonic turbulence are ubiquitously found at early stages

The role of turbulence in high-mass star formation: Subsonic and transonic turbulence are ubiquitously found at early stages

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde

Massive Star Formation Starts in Subvirial Dense Clumps Unless Resisted by Strong Magnetic Fields

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