Dense gas formation in the Musca filament due to the dissipation of a supersonic converging flow

Bonne, Lars; Schneider, N.; Bontemps, Sylvain; Clarke, S. D.; Gusdorf, A.; Lehmann, A.; Steinke, M.; Csengeri, T.; Kabanovic, S.; Simon, R.; Buchbender, C.; Güsten, R.

doi:10.1051/0004-6361/201937104

Cited by 28 publications

(28 citation statements)

References 96 publications

(128 reference statements)

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“…Panopoulou et al 2017;Seifried et al 2017;Ossenkopf-Okada & Stepanov 2019), filament width of 0.1 pc in nearby molecular clouds is close to the sonic scale which could fit in a scenario where filaments are made of dense, post-shock gas of converging flows (Arzoumanian et al 2011;Schneider et al 2011;Federrath 2016). In the companion paper (Bonne et al 2020), observational indications were found of warm gas from low-velocity shocks associated with mass accretion on the Musca filament. It has also led to some theoretical models considering gravitational inflow that might provide an explanation for this universal width (Heitsch 2013;Hennebelle & André 2013).…”

Section: Introductionmentioning

confidence: 94%

Formation of the Musca filament: evidence for asymmetries in the accretion flow due to a cloud–cloud collision

Bonne

Bontemps

Schneider

et al. 2020

A&A

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Context. Dense molecular filaments are ubiquituous in the interstellar medium, yet their internal physical conditions and the role of gravity, turbulence, the magnetic field, radiation, and the ambient cloud during their evolution remain debated. Aims. We study the kinematics and physical conditions in the Musca filament, the ambient cloud, and the Chamaeleon-Musca complex to constrain the physics of filament formation. Methods. We produced CO(2–1) isotopologue maps with the APEX telescope that cut through the Musca filament. We further study a NANTEN2 12CO(1–0) map of the full Musca cloud, H I emission of the Chamaeleon-Musca complex, a Planck polarisation map, line radiative transfer models, Gaia data, and synthetic observations from filament formation simulations. Results. The Musca cloud, with a size of ~3–6 pc, contains multiple velocity components. Radiative transfer modelling of the CO emission indicates that the Musca filament consists of a cold (~10 K), dense (nH2 ∼ 104 cm−3) crest, which is best described with a cylindrical geometry. Connected to the crest, a separate gas component at T ~ 15 K and nH2 ∼ 103 cm−3 is found, the so-called strands. The velocity-coherent filament crest has an organised transverse velocity gradient that is linked to the kinematics of the nearby ambient cloud. This velocity gradient has an angle ≥30° with respect to the local magnetic field orientation derived from Planck, and the magnitude of the velocity gradient is similar to the transonic linewidth of the filament crest. Studying the large scale kinematics, we find coherence of the asymmetric kinematics from the 50 pc H I cloud down to the Musca filament. We also report a strong [C18O]/[13CO] abundance drop by an order of magnitude from the filament crest to the strands over a distance <0.2 pc in a weak ambient far-ultraviolet (FUV) field. Conclusions. The dense Musca filament crest is a long-lived (several crossing times), dynamic structure that can form stars in the near future because of continuous mass accretion replenishing the filament. This mass accretion on the filament appears to be triggered by a H I cloud–cloud collision, which bends the magnetic field around dense filaments. This bending of the magnetic field is then responsible for the observed asymmetric accretion scenario of the Musca filament, which is, for instance, seen as a V-shape in the position–velocity (PV) diagram.

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Section: Introductionmentioning

confidence: 94%

Formation of the Musca filament: evidence for asymmetries in the accretion flow due to a cloud–cloud collision

Bonne

Bontemps

Schneider

et al. 2020

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“…In order to stabilise the filamentary structure we instead assume a radial inflow in our idealised simulations. Such radial accretion flows have been observed in many filaments (Schneider et al 2010;Kirk et al 2013;Palmeirim et al 2013;Shimajiri et al 2019;Bonne et al 2020) and typically show estimated accretion rates of around 10 − 100 M pc −1 Myr −1 and accretion velocities of the order of 0.25 − 1.0 km s −1 . If we assume a shock inflow region feeding the filament of around 0.5 pc, this would lead to a sustained inflow of material on timescales of 0.5-2 Myr.…”

Section: Introductionmentioning

confidence: 83%

Taking off the edge -- simultaneous filament and end core formation

Heigl¹,

Hoemann²,

Burkert³

2021

Preprint

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Simulations of idealised star-forming filaments of finite length typically show core growth which is dominated by two cores forming at its respective end. The end cores form due to a strong increasing acceleration at the filament ends which leads to a sweep-up of material during the filament collapse along its axis. As this growth mode is typically faster than any other core formation mode in a filament, the end cores usually dominate in mass and density compared to other cores forming inside a filament. However, observations of star-forming filaments often do not show this prevalence of cores at the filament edges. We use numerical simulations of accreting filaments forming in a finite converging flow to explore a possible mechanism which leads to a suppression of the end cores. While such a setup still leads to end cores that soon begin to move inwards, the continued accumulation of material outside of these makes a key difference: their positions now lie within the larger filamentary structure and not at its edges. This softens their inward gravitational acceleration as they are embedded by new material further out. As a result, these two cores do not grow as fast as expected for the edge effect and thus do not dominate over other core formation modes in the filament.

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“…Furthermore, Herschel observations reveal a network of striations orthogonal to the filament, which are thought to be indications of mass inflow along the magnetic field (Cox et al 2016). An indication of continuous mass accretion from inflow toward the Musca filament was found by observed presence of low-velocity filament accretion shocks around the Musca filament (Bonne et al 2020b). Hacar et al (2016) conclude from individual 13 CO and C 18 O pointings that the crest of the Musca filament is a single velocity-coherent structure.…”

Section: The Musca Cloud: Herschel Flux Density Mapmentioning

confidence: 95%

“…Musca is a prominent filamentary structure, 6 pc in length, with a high aspect ratio at a distance of only 140-150 pc (Hacar et al 2016;Cox et al 2016;Kainulainen et al 2016;Gaia Collaboration 2018). It has a low average column density N, with N(max) ∼ 4-8 10 21 cm −2 (Bonne et al 2020b), and shows only one protostellar source located at the northern end of the filament (Juvela et al 2012;Machaieie et al 2017). Furthermore, Herschel observations reveal a network of striations orthogonal to the filament, which are thought to be indications of mass inflow along the magnetic field (Cox et al 2016).…”

Section: The Musca Cloud: Herschel Flux Density Mapmentioning

confidence: 99%

Description of turbulent dynamics in the interstellar medium: multifractal-microcanonical analysis

Yahia

Schneider

Bontemps

et al. 2021

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Observations of the interstellar medium (ISM) show a complex density and velocity structure, which is in part attributed to turbulence. Consequently, the multifractal formalism should be applied to observation maps of the ISM in order to characterize its turbulent and multiplicative cascade properties. However, the multifractal formalism, even in its more advanced and recent canonical versions, requires a large number of realizations of the system, which usually cannot be obtained in astronomy. We present a self-contained introduction to the multifractal formalism in a "microcanonical" version, which allows us, for the first time, to compute precise turbulence characteristic parameters from a single observational map without the need for averages in a grand ensemble of statistical observables (e.g., a temporal sequence of images). We compute the singularity exponents and the singularity spectrum for both observations and magnetohydrodynamic simulations, which include key parameters to describe turbulence in the ISM. For the observations we focus on the 250 µm Herschel map of the Musca filament. Scaling properties are investigated using spatial 2D structure functions, and we apply a two-point log-correlation magnitude analysis over various lines of the spatial observation, which is known to be directly related to the existence of a multiplicative cascade under precise conditions. It reveals a clear signature of a multiplicative cascade in Musca with an inertial range from 0.05-0.65 pc. We show that the proposed microcanonical approach provides singularity spectra that are truly scale invariant, as required to validate any method used to analyze multifractality. The obtained singularity spectrum of Musca, which is sufficiently precise for the first time, is clearly not as symmetric as usually observed in log-normal behavior. We claim that the singularity spectrum of the ISM toward Musca features a more log-Poisson shape. Since log-Poisson behavior is claimed to exist when dissipation is stronger for rare events in turbulent flows, in contrast to more homogeneous (in volume and time) dissipation events, we suggest that this deviation from log-normality could trace enhanced dissipation in rare events at small scales, which may explain, or is at least consistent with, the dominant filamentary structure in Musca. Moreover, we find that subregions in Musca tend to show different multifractal properties: While a few regions can be described by a log-normal model, other regions have singularity spectra better fitted by a log-Poisson model. This strongly suggests that different types of dynamics exist inside the Musca cloud. We note that this deviation from log-normality and these differences between subregions appear only after reducing noise features, using a sparse edge-aware algorithm, which have the tendency to "log-normalize" an observational map. Implications for the star formation process are discussed. Our study establishes fundamental tools that will be applied to other galactic clouds and simulations in forthcom...

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Dense gas formation in the Musca filament due to the dissipation of a supersonic converging flow

Cited by 28 publications

References 96 publications

Formation of the Musca filament: evidence for asymmetries in the accretion flow due to a cloud–cloud collision

Formation of the Musca filament: evidence for asymmetries in the accretion flow due to a cloud–cloud collision

Taking off the edge -- simultaneous filament and end core formation

Description of turbulent dynamics in the interstellar medium: multifractal-microcanonical analysis

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