Ion-neutral friction and accretion-driven turbulence in self-gravitating filaments

Hennebelle, P.; André, P.

doi:10.1051/0004-6361/201321761

Cited by 67 publications

(71 citation statements)

References 28 publications

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“…The pattern observed in Musca is reminiscent of the situation seen around the Taurus B211/3 filament system, where velocity information is consistent with accretion of low-density striations onto the denser B211/3 filament (Goldsmith et al 2008;Palmeirim et al 2013). Hennebelle & André (2013) and Heitsch (2013a,b) independently proposed analytical toy models -based on accretiondriven MHD turbulence -which link the observed accretion phenomenon to the physical reason why supercritical filaments can maintain a roughly constant inner width ∼0.1 pc (Arzoumanian et al 2011) while they should normally contract radially with time (see also the velocity dispersion "evolution" observed by Arzoumanian et al 2013). Both models emphasize the role of continuing accretion in explaining the observed properties of dense filaments.…”

Section: Magnetically-controlled Cloud and Filament Formationmentioning

confidence: 60%

“…Alternatively, the characteristic width may be set by the dissipation mechanism of magneto-hydrodynamic (MHD) waves due to ion-neutral friction (i.e., ambipolar diffusion) in weakly ionized molecular filaments (Hennebelle 2013;Ntormousi et al 2016). For dense, self-gravitating filaments, continuous accretion of A&A 590, A110 (2016) 12h25m 00.00s 30m 00.00s 35m 00.00s 40m 00.00s RA(J2000) background cloud material likely plays a key role (Arzoumanian et al 2013;Heitsch 2013a,b;Hennebelle & André 2013). Interestingly, filamentary structures are also seen, albeit on different scales, in the molecular material associated with regions of high-mass star-and cluster-formation, such as DR21 (Schneider et al 2010) and Serpens .…”

Section: Introductionmentioning

confidence: 99%

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Filamentary structure and magnetic field orientation in Musca

Cox

Arzoumanian

André

et al. 2016

A&A

122

187

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Herschel has shown that filamentary structures are ubiquitous in star-forming regions, in particular in nearby molecular clouds associated with Gould's Belt. High dynamic range far-infrared imaging of the Musca cloud with SPIRE and PACS reveals at least two types of filamentary structures: (1) the main ∼10-pc scale high column-density linear filament; and (2) low column-density striations in close proximity to the main filament. In addition, we find features with intermediate column densities (hair-like strands) that appear physically connected to the main filament. We present an analysis of this filamentary network traced by Herschel and explore its connection with the local magnetic field. We find that both the faint dust emission striations and the plane-of-the-sky (POS) magnetic field are locally oriented close to perpendicular to the high-density main filament (position angle ∼25−35 • ). The low-density striations and strands are oriented parallel to the POS magnetic field lines, which are derived previously from optical polarization measurements of background stars and more recently from Planck observations of dust polarized emission. The position angles are 97 ± 25 • , 105 ± 7 • , and 105 ± 5 • . From these observations, we propose a scenario in which local interstellar material in this cloud has condensed into a gravitationally-unstable filament (with "supercritical" mass per unit length) that is accreting background matter along field lines through the striations. We also compare the filamentary structure in Musca with what is seen in similar Herschel observations of the Taurus B211/3 filament system and find that there is significantly less substructure in the Musca main filament than in the B211/3 filament. We suggest that the Musca cloud may represent an earlier evolutionary stage in which the main filament has not yet accreted sufficient mass and energy to develop a multiple system of intertwined filamentary components.

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Section: Magnetically-controlled Cloud and Filament Formationmentioning

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Filamentary structure and magnetic field orientation in Musca

Cox

Arzoumanian

André

et al. 2016

A&A

122

187

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“…At the same time, Hennebelle & André (2013) suggested through simple analytical calculations that, in the case of self-gravitating molecular clouds, ion-neutral friction (also called ambipolar diffusion) could be the process behind the constant filament thickness. In short, the argument in Hennebelle & André (2013) is that mass accretion onto a filament drives turbulence in its interior, which is constantly dissipated through ambipolar diffusion. In contrast to Heitsch (2013), in this theory it is the balance between accretion-driven turbulence and dissipation that keeps the thickness of the filament almost independent of density as it gains mass.…”

Section: Introductionmentioning

confidence: 99%

“…This length was derived by Kulsrud & Pearce (1969) in the context of cosmic ray interactions with the interstellar medium. However, it been used in star formation theory for estimating relevant timescales for prestellar cores (Mouschovias 1991) and was also the basis of the theory presented in Hennebelle & André (2013):…”

Section: Introductionmentioning

confidence: 99%

The effect of ambipolar diffusion on low-density molecular ISM filaments

Ntormousi

Hennebelle

André

et al. 2016

A&A

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Context. The filamentary structure of the molecular interstellar medium and the potential link of this morphology to star formation have been brought into focus recently by high resolution observational surveys. An especially puzzling matter is that local interstellar filaments appear to have the same thickness, independent of their column density. This requires a theoretical understanding of their formation process and the physics that governs their evolution. Aims. In this work we explore a scenario in which filaments are dissipative structures of the large-scale interstellar turbulence cascade and ion-neutral friction (also called ambipolar diffusion) is affecting their sizes by preventing small-scale compressions. Methods. We employ high-resolution (512 3 and 1024 3 ), 3D magnetohydrodynamic (MHD) simulations, performed with the grid code RAMSES, to investigate non-ideal MHD turbulence as a filament formation mechanism. We focus the analysis on the mass and thickness distributions of the resulting filamentary structures. Results. Simulations of both driven and decaying MHD turbulence show that the morphologies of the density and the magnetic field are different when ambipolar diffusion is included in the models. In particular, the densest structures are broader and more massive as an effect of ion-neutral friction and the power spectra of both the velocity and the density steepen at a smaller wavenumber. Conclusions. The comparison between ideal and non-ideal MHD simulations shows that ambipolar diffusion causes a shift of the filament thickness distribution towards higher values. However, none of the distributions exhibit the pronounced peak found in the observed local filaments. Limitations in dynamical range and the absence of self-gravity in these numerical experiments do not allow us to conclude at this time whether this is due to the different filament selection or due to the physics inherent of the filament formation.

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“…Turbulent energy in the ISM is dissipated via either viscous (hydrodynamical) or resistive (MHD) processes, depending on which process happens at the largest scale (Benjamin 1999;Hennebelle & André 2013). The scale at which turbulent energy is dissipated is…”

Section: Dissipation Scalementioning

confidence: 99%

Structure formation in a colliding flow: The Herschel view of the Draco nebula

Miville-Deschênes

Salomé

Martín

et al. 2017

A&A

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Context. The Draco nebula is a high Galactic latitude interstellar cloud observed at velocities corresponding to the intermediate velocity cloud regime. This nebula shows unusually strong CO emission and remarkably high-contrast small-scale structures for such a diffuse high Galactic latitude cloud. The 21 cm emission of the Draco nebula reveals that it is likely to have been formed by the collision of a cloud entering the disk of the Milky Way. Such physical conditions are ideal to study the formation of cold and dense gas in colliding flows of diffuse and warm gas. Aims. The objective of this study is to better understand the process of structure formation in a colliding flow and to describe the effects of matter entering the disk on the interstellar medium. Methods. We conducted Herschel-SPIRE observations of the Draco nebula. The clumpfind algorithm was used to identify and characterize the small-scale structures of the cloud. Results. The high-resolution SPIRE map reveals the fragmented structure of the interface between the infalling cloud and the Galactic layer. This front is characterized by a Rayleigh-Taylor (RT) instability structure. From the determination of the typical length of the periodic structure (2.2 pc) we estimated the gas kinematic viscosity. This allowed us to estimate the dissipation scale of the warm neutral medium (0.1 pc), which was found to be compatible with that expected if ambipolar diffusion were the main mechanism of turbulent energy dissipation. The statistical properties of the small-scale structures identified with clumpfind are found to be typical of that seen in molecular clouds and hydrodynamical turbulence in general. The density of the gas has a log-normal distribution with an average value of 10 3 cm −3 . The typical size of the structures is 0.1−0.2 pc, but this estimate is limited by the resolution of the observations. The mass of these structures ranges from 0.2 to 20 M and the distribution of the more massive structures follows a power-law dN/dlog(M) ∼ M −1.4 . We identify a mass-size relation with the same exponent as that found in molecular clouds (M ∼ L 2.3 ). On the other hand, we found that only 15% of the mass of the cloud is in gravitationally bound structures. Conclusions. We conclude that the collision of diffuse gas from the Galactic halo with the diffuse interstellar medium of the outer layer of the disk is an efficient mechanism for producing dense structures. The increase of pressure induced by the collision is strong enough to trigger the formation of cold neutral medium out of the warm gas. It is likely that ambipolar diffusion is the mechanism dominating the turbulent energy dissipation. In that case the cold structures are a few times larger than the energy dissipation scale. The dense structures of Draco are the result of the interplay between magnetohydrodynamical turbulence and thermal instability as self-gravity is not dominating the dynamics. Interestingly they have properties typical of those found in more classical molecular clouds.

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Ion-neutral friction and accretion-driven turbulence in self-gravitating filaments

Cited by 67 publications

References 28 publications

Filamentary structure and magnetic field orientation in Musca

Filamentary structure and magnetic field orientation in Musca

The effect of ambipolar diffusion on low-density molecular ISM filaments

Structure formation in a colliding flow: The Herschel view of the Draco nebula

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