Magnetically Aligned Velocity Anisotropy in the Taurus Molecular Cloud

Heyer, M. H.; Gong, Hao; Ostriker, Eve C.; Brunt, Christopher M.

doi:10.1086/587510

Cited by 144 publications

(190 citation statements)

References 25 publications

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“…For example, Palmeirim et al (2013) observed striations perpendicular to the Taurus B211/3 filament and argued that these were tracing mass accretion. These striations are approximately parallel to the projected plane of the sky magnetic field, as traced by optical polarization (Chapman et al 2011;Heiles 2000;Heyer et al 2008). Fiege & Pudritz (2000a,b) argue that such a shallow (r −2 ) density profile as that estimated in B211/3 would be consistent with models of filaments in isothermal equilibrium that are threaded by helical magnetic fields.…”

Section: Molecular Cloud Formationmentioning

confidence: 79%

Slingshot mechanism in Orion: Kinematic evidence for ejection of protostars by filaments

Stutz

Gould

2016

A&A

130

260

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By comparing three constituents of Orion A (gas, protostars, and pre-main-sequence stars), both morphologically and kinematically, we derive the following conclusions. The gas surface density near the integral-shaped filament (ISF) is very well represented by a power law, Σ(b) = 37 M pc −2 (b/pc) −5/8 , for the entire range to which we are sensitive, 0.05 pc < b < 8.5 pc, of projected separation from the filament ridge. Essentially all Class 0 and Class I protostars lie superposed on the ISF or on identifiable filament ridges farther south, while almost all pre-main-sequence (Class II) stars do not. Combined with the fact that protostars are moving < ∼ 1 km s −1 relative to the filaments, while stars are moving several times faster, this implies that protostellar accretion is terminated by a slingshot-like "ejection" from the filaments. The ISF is the third in a series of identifiable star bursts that are progressively moving south, with separations of several Myr in time and 2-3 pc in space. This, combined with the observed undulations in the filament (both spatial and velocity), suggest that repeated propagation of transverse waves through the filament is progressively digesting the material that formerly connected Orion A and B into stars in discrete episodes. We construct a simple, circularly symmetric gas density profile ρ(r) = 17 M pc −3 (r/pc) −13/8 consistent with the two-dimensional data. The model implies that the observed magnetic fields in this region are subcritical on spatial scales of the observed undulations, suggesting that the transverse waves propagating through the filament are magnetically induced. Because the magnetic fields are supercritical on scales of the filament as a whole (as traced by the power law), the system as a whole is relatively stable and long lived. Protostellar "ejection" (i.e., the slingshot) occurs because the gas accelerates away from the protostars, not the other way around. The model also implies that the ISF is kinematically young, which is consistent with several other lines of evidence. In contrast to the ISF, the southern filament (L1641) has a broken power law, which matches the ISF profile for 2.5 pc < b < 8.5 pc, but is shallower closer in. L1641 is kinematically older than the ISF.

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Section: Molecular Cloud Formationmentioning

confidence: 79%

Slingshot mechanism in Orion: Kinematic evidence for ejection of protostars by filaments

Stutz

Gould

2016

A&A

130

260

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“…For instance, the IMF model by requires magnetic fields to explain the present-day mass function, while it is still not clear whether magnetic fields are dynamically important for typical molecular clouds. However, Heyer et al (2008) showed that magnetohydrodynamic turbulence in the Taurus MC may lead to an alignment of flows along the field lines. -The present study did not include the effects of self-gravity, because we specifically focus on the pure turbulence statistics obtained in solenoidal and compressive forcings.…”

Section: Limitationsmentioning

confidence: 99%

Comparing the statistics of interstellar turbulence in simulations and observations

Federrath

Duval

Klessen³

et al. 2010

A&A

798

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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“…These include threepoint statistics, such as the bispectrum studied here and in Burkhart et al (2009Burkhart et al ( , 2010. Furthermore, it was recently shown in Correia et al (2016) that the principle component analysis (PCA; see Heyer & Schloerb 1997;Heyer et al 2008) is sensitive to the phase information. Intermittency studies also utilize phase information (see Cho & Lazarian 2003;Kowal et al 2007).…”

Section: Discussionmentioning

confidence: 91%

“…Probability distribution functions of column densities, including different measures obtained with them, e.g., skewness and kurtosis (Burkhart et al 2009(Burkhart et al , 2010, Tsalis statistics (Esquivel & Lazarian 2010;Toffelmire, Burkhart & Lazarian 2011), and dispersion (Burkhart & Lazarian 2012), were considered as tools to obtain the properties of turbulence from observations. Together with the techniques for the anisotropy of turbulence studies Esquivel & Lazarian 2011;Heyer et al 2008;Burkhart et al 2014) and intermittency studies (Padoan et al 2004;Kowal et al 2007), they present an impressive toolbox for quantitative studies of interstellar turbulence.…”

Section: Discussionmentioning

confidence: 99%

The Phase Coherence of Interstellar Density Fluctuations

Burkhart

Lazarían

2016

ApJ

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Studies of MHD turbulence often investigate the Fourier power spectrum to provide information on the nature of the turbulence cascade. However, the Fourier power spectrum only contains the Fourier amplitudes and rejects all information regarding the Fourier phases. Here, we investigate the utility of two statistical diagnostics for recovering information on Fourier phases in ISM column density maps: the averaged amplitudes of the bispectrum and the phase coherence index (PCI), a new phase technique for the ISM. We create three-dimensional density and two-dimensional column density maps using a set of simulations of isothermal ideal MHD turbulence with a wide range of sonic and Alfvénic Mach numbers. We find that the bispectrum averaged along different angles with respect to either the k 1 or k 2 axis is primarily sensitive to the sonic Mach number while averaging the bispectral amplitudes over different annuli is sensitive to both the sonic and Alfvénic Mach numbers. The PCI of density suggests that the most correlated phases occur in supersonic sub-Alfvénic turbulence and near the shock scale. This suggests that nonlinear interactions with correlated phases are strongest in shock-dominated regions, in agreement with findings from the solar wind. Our results suggest that the phase information contained in the bispectrum and PCI can be used to find the turbulence parameters in column density maps.

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Magnetically Aligned Velocity Anisotropy in the Taurus Molecular Cloud

Cited by 144 publications

References 25 publications

Slingshot mechanism in Orion: Kinematic evidence for ejection of protostars by filaments

Slingshot mechanism in Orion: Kinematic evidence for ejection of protostars by filaments

Comparing the statistics of interstellar turbulence in simulations and observations

The Phase Coherence of Interstellar Density Fluctuations

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