On the structure of the turbulent interstellar clouds

Audit, E.; Hennebelle, P.

doi:10.1051/0004-6361/200912695

Cited by 103 publications

(111 citation statements)

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“…The simulations reported here are very similar to those presented by and Audit & Hennebelle (2010). They were performed with the adaptive meshrefinement magnetohydrodynamics code RAMSES (Teyssier 2002;Fromang et al 2006) and include magnetic fields (initially uniform and equal to 5 μG) and self-gravity.…”

Section: Estimate Of Efficiencymentioning

confidence: 79%

“…Audit & Hennebelle 2005;Heitsch et al 2005Heitsch et al , 2006aFolini & Walder 2006;Vázquez-Semadeni et al 2006Banerjee et al 2009;Audit & Hennebelle 2010). These simulations consider two colliding flows of diffuse gas that produce strong density fluctuations of cold gas.…”

Section: Estimate Of Efficiencymentioning

confidence: 99%

“…Finally, we see that the efficiency is greater in the isothermal case by a factor of ∼3 compared to the low-resolution runs with cooling. This indicates that the thermal structure of the flow has a significant impact on its dynamics (see also Audit & Hennebelle 2010). Because the isothermal run and the simulations with a 2-phase medium cooling function are significantly different, the discrepancy gives us an estimate of the uncertainty of the efficiency.…”

Section: Estimate Of Efficiencymentioning

confidence: 99%

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Accretion-driven turbulence as universal process: galaxies, molecular clouds, and protostellar disks

Klessen¹,

Hennebelle²

2010

A&A

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321

353

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Context. Even though turbulent motions are found everywhere in astrophysical systems, the origin of this turbulence is poorly understood. When cosmic structures form, they grow in mass via accretion from their surrounding environment. Aims. We propose that accretion is able to drive internal turbulent motions in a wide range of astrophysical objects and study this process in the case of galaxies, molecular clouds, and protoplanetary disks. Methods. We use a combination of numerical simulations and analytical arguments to predict the level of turbulence as a function of the accretion rate, the dissipation scale, and the density contrast, and compare our models with observational data. Results. We find that in Milky Way type galaxies the observed level of turbulence in the interstellar medium can be explained by accretion, provided that the galaxies gain mass at a rate comparable to the rate at which they form stars. This process is particularly relevant in the extended outer disks beyond the star-forming radius. For it to drive turbulence in dwarf galaxies, the accretion rate needs to exceed the star formation rate by a large factor, so we expect other sources to dominate. We also calculate the rate at which molecular clouds grow in mass when they build up from the atomic component of the galactic gas and find that their internal turbulence is likely to be driven by accretion as well. It is the very process of cloud formation that excites turbulent motions on small scales by establishing the turbulent cascade. In the case of T Tauri disks, we show that accretion can drive subsonic turbulence if the rate at which gas falls onto the disk is comparable to the rate at which disk material accretes onto the central star. This also explains the observed relation of accretion rate and stellar mass,Ṁ ∝ M 1.8 . The efficiency required to convert infall motion into turbulence is a few percent in all three cases. Conclusions. We conclude that accretion-driven turbulence is a universal concept with far-reaching implications for a wide range of astrophysical objects.

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Section: Estimate Of Efficiencymentioning

confidence: 79%

Section: Estimate Of Efficiencymentioning

confidence: 99%

Section: Estimate Of Efficiencymentioning

confidence: 99%

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Accretion-driven turbulence as universal process: galaxies, molecular clouds, and protostellar disks

Klessen¹,

Hennebelle²

2010

A&A

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321

353

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“…Although many of these "cores" here are transient, some of them are dense enough to become gravitationally bound, and accumulate enough mass to decouple from the overall supersonic turbulent flow. See the online version for a movie, showing the time evolution of this figure. statistics (e.g., Li et al 2003;Audit & Hennebelle 2010). The results of the present study apply primarily to the dense interstellar molecular gas for which an isothermal equation of state is an adequate approximation (Wolfire et al 1995;Ferrière 2001;Pavlovski et al 2006;Glover et al 2010).…”

Section: Limitationsmentioning

confidence: 86%

Comparing the statistics of interstellar turbulence in simulations and observations

Federrath

Duval

Klessen³

et al. 2010

A&A

833

101

1,286

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Context. Density and velocity fluctuations on virtually all scales observed with modern telescopes show that molecular clouds (MCs) are turbulent. The forcing and structural characteristics of this turbulence are, however, still poorly understood. Aims. To shed light on this subject, we study two limiting cases of turbulence forcing in numerical experiments: solenoidal (divergence-free) forcing and compressive (curl-free) forcing, and compare our results to observations. Methods. We solve the equations of hydrodynamics on grids with up to 1024 3 cells for purely solenoidal and purely compressive forcing. Eleven lower-resolution models with different forcing mixtures are also analysed. Results. Using Fourier spectra and Δ-variance, we find velocity dispersion-size relations consistent with observations and independent numerical simulations, irrespective of the type of forcing. However, compressive forcing yields stronger compression at the same rms Mach number than solenoidal forcing, resulting in a three times larger standard deviation of volumetric and column density probability distributions (PDFs). We compare our results to different characterisations of several observed regions, and find evidence of different forcing functions. Column density PDFs in the Perseus MC suggest the presence of a mainly compressive forcing agent within a shell, driven by a massive star. Although the PDFs are close to log-normal, they have non-Gaussian skewness and kurtosis caused by intermittency. Centroid velocity increments measured in the Polaris Flare on intermediate scales agree with solenoidal forcing on that scale. However, Δ-variance analysis of the column density in the Polaris Flare suggests that turbulence is driven on large scales, with a significant compressive component on the forcing scale. This indicates that, although likely driven with mostly compressive modes on large scales, turbulence can behave like solenoidal turbulence on smaller scales. Principal component analysis of G216-2.5 and most of the Rosette MC agree with solenoidal forcing, but the interior of an ionised shell within the Rosette MC displays clear signatures of compressive forcing. Conclusions. The strong dependence of the density PDF on the type of forcing must be taken into account in any theory using the PDF to predict properties of star formation. We supply a quantitative description of this dependence. We find that different observed regions show evidence of different mixtures of compressive and solenoidal forcing, with more compressive forcing occurring primarily in swept-up shells. Finally, we emphasise the role of the sonic scale for protostellar core formation, because core formation close to the sonic scale would naturally explain the observed subsonic velocity dispersions of protostellar cores.

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“…(e.g., Padoan, Jones, & Nordlund 1997;Federrath, Klessen, & Schmidt 2008;Audit & Hennebelle 2010;Federrath et al 2010 andKim 2013); σ , being the full width at half-maximum. The PDF for Case 1, on the other hand, appears to be developing a power-law tail at higher densities.…”

Section: Some Diagnostic Properties Of Gasmentioning

confidence: 99%

Formation of Prestellar Cores via Non-Isothermal Gas Fragmentation

Anathpindika

2015

Publ. Astron. Soc. Aust.

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Sheet-like clouds are common in turbulent gas and perhaps form via collisions between turbulent gas flows. Having examined the evolution of an isothermal shocked slab in an earlier contribution, in this work we follow the evolution of a sheet-like cloud confined by (thermal) pressure and gas in it is allowed to cool. The extant purpose of this endeavour is to study the early phases of core-formation. The observed evolution of this cloud supports the conjecture that molecular clouds themselves are three-phase media (comprising viz. a stable cold and warm medium, and a third thermally unstable medium), though it appears, clouds may evolve in this manner irrespective of whether they are gravitationally bound. We report, this sheet fragments initially due to the growth of the thermal instability (TI) and some fragments are elongated, filament-like. Subsequently, relatively large fragments become gravitationally unstable and sub-fragment into smaller cores. The formation of cores appears to be a three stage process: first, growth of the TI leads to rapid fragmentation of the slab; second, relatively small fragments acquire mass via gas-accretion and/or merger and third, sufficiently massive fragments become susceptible to the gravitational instability and sub-fragment to form smaller cores. We investigate typical properties of clumps (and smaller cores) resulting from this fragmentation process. Findings of this work support the suggestion that the weak velocity field usually observed in dense clumps and smaller cores is likely seeded by the growth of dynamic instabilities. Simulations were performed using the smooth particle hydrodynamics algorithm.

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On the structure of the turbulent interstellar clouds

Cited by 103 publications

References 50 publications

Accretion-driven turbulence as universal process: galaxies, molecular clouds, and protostellar disks

Accretion-driven turbulence as universal process: galaxies, molecular clouds, and protostellar disks

Comparing the statistics of interstellar turbulence in simulations and observations

Formation of Prestellar Cores via Non-Isothermal Gas Fragmentation

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