Striations in molecular clouds: streamers or MHD waves?

Tritsis, Aris; Tassis, Konstantinos

doi:10.1093/mnras/stw1881

Cited by 38 publications

(41 citation statements)

References 47 publications

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“…Striations, a network of faint and elongated density structures aligned along the magnetic field, are found in the low-column density (N H ≈ 1 − 2 × 10 21 cm −2 ) regions in MCs (Goldsmith et al 2008;Heyer et al 2016). The high velocity gradient transverse to the magnetic field compared to that along the field direction ) and the spatial power spectrum transverse to the magnetic field (Tritsis & Tassis 2016) provide strong observational evidence for anisotropic turbulent mixing as the mechanism of their formation.…”

Section: Examples For Low-density Parallel Filaments In the Ismmentioning

confidence: 97%

On the Formation of Density Filaments in the Turbulent Interstellar Medium

Xu¹,

Lazarían³

2019

ApJ

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This study is motivated by recent observations on ubiquitous interstellar density filaments and guided by modern theories of compressible magnetohydrodynamic (MHD) turbulence. The interstellar turbulence shapes the observed density structures. As the fundamental dynamics of compressible MHD turbulence, perpendicular turbulent mixing of density fluctuations entails elongated density structures aligned with the local magnetic field, accounting for low-density parallel filaments seen in diffuse atomic and molecular gas. The elongation of low-density parallel filaments depends on the turbulence anisotropy. When taking into account the partial ionization, we find that the minimum width of parallel filaments in the cold neutral medium and molecular clouds is determined by the neutral-ion decoupling scale perpendicular to magnetic field. In highly supersonic MHD turbulence in molecular clouds, both low-density parallel filaments due to anisotropic turbulent mixing and high-density filaments due to shock compression exist.

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Section: Examples For Low-density Parallel Filaments In the Ismmentioning

confidence: 97%

On the Formation of Density Filaments in the Turbulent Interstellar Medium

Xu¹,

Lazarían³

2019

ApJ

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“…Heyer et al, 2016), where they appear as highly elongated along the magnetic field. Tritsis & Tassis (2016) have performed several numerical calculations to investigate their origin and concluded that they are most likely a consequence of non-linear MHD waves due to inhomogeneous density fields. Similar conclusion has been reached by Chen & Ostriker (2014) who presented a series of magnetized simulations and identified a network of small filaments aligned with the magnetic field in the simulations with the lowest β and estimate that this later must be < 0.2 to get prominent striations.…”

Section: Formation Of Filamentsmentioning

confidence: 99%

The Role of Magnetic Field in Molecular Cloud Formation and Evolution

Hennebelle

Inutsuka

2019

Front. Astron. Space Sci.

199

124

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We review the role that magnetic field may have on the formation and evolution of molecular clouds. After a brief presentation and main assumptions leading to ideal MHD equations, their most important correction, namely the ion-neutral drift is described. The nature of the multi-phase interstellar medium (ISM) and the thermal processes that allows this gas to become denser are presented. Then we discuss our current knowledge of compressible magnetized turbulence, thought to play a fundamental role in the ISM. We also describe what is known regarding the correlation between the magnetic and the density fields. Then the influence that magnetic field may have on the interstellar filaments and the molecular clouds is discussed, notably the role it may have on the prestellar dense cores as well as regarding the formation of stellar clusters. Finally we briefly review its possible effects on the formation of molecular clouds themselves. We argue that given the magnetic intensities that have been measured, it is likely that magnetic field is i) responsible of reducing the star formation rate in dense molecular cloud gas by a factor of a few, ii) strongly shaping the interstellar gas by generating a lot of filaments and reducing the numbers of clumps, cores and stars, although its exact influence remains to be better understood. Moreover at small scales, magnetic braking is likely a dominant process that strongly modifies the outcome of the star formation process. Finally, we stress that by inducing the formation of more massive stars, magnetic field could possibly enhance the impact of stellar feedback.

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“…Magnetic fields also may play a role in feedback, for example, by driving protostellar jets that inject mass, momentum and energy into the medium, possibly stirring turbulent motions (Frank et al 2014;Gerrard et al 2019;Krumholz & Federrath 2019;. They also seem to play a role in the orientation of filamentary structures and striations in the MCs which may not directly influence the star-forming potential of the cloud, but certainly influences the global structure of the cloud through the density PDF (Planck Collaboration et al 2016a,b;Cox et al 2016;Malinen et al 2016;Soler et al 2017;Tritsis & Tassis 2016;Soler 2019). High-density filamentary structures house the local conditions necessary to overcome the turbulent motions, and observations find protostars located at junctions (or hubs) between intersecting filaments (André et al 2010;Men'shchikov et al 2010;Schneider et al 2013;Arzoumanian et al 2018;Tokuda et al 2018;Trevino-Morales et al 2019;Roy et al 2019;Xu et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Filaments and striations: anisotropies in observed, supersonic, highly magnetized turbulent clouds

Beattie

Federrath

2019

Monthly Notices of the Royal Astronomical Society

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Stars form in highly-magnetised, supersonic turbulent molecular clouds. Many of the tools and models that we use to carry out star formation studies rely upon the assumption of cloud isotropy. However, structures like high-density filaments in the presence of magnetic fields, and magnetosonic striations introduce anisotropies into the cloud. In this study we use the two-dimensional (2D) power spectrum to perform a systematic analysis of the anisotropies in the column density for a range of Alfvén Mach numbers (M A = 0.1-10) and turbulent Mach numbers (M = 2-20), with 20 highresolution, three-dimensional (3D) turbulent magnetohydrodynamic simulations. We find that for cases with a strong magnetic guide field, corresponding to M A < 1, and M 4, the anisotropy in the column density is dominated by thin striations aligned with the magnetic field, while for M 4 the anisotropy is significantly changed by high-density filaments that form perpendicular to the magnetic guide field. Indeed, the strength of the magnetic field controls the degree of anisotropy and whether or not any anisotropy is present, but it is the turbulent motions controlled by M that determine which kind of anisotropy dominates the morphology of a cloud.

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Striations in molecular clouds: streamers or MHD waves?

Cited by 38 publications

References 47 publications

On the Formation of Density Filaments in the Turbulent Interstellar Medium

On the Formation of Density Filaments in the Turbulent Interstellar Medium

The Role of Magnetic Field in Molecular Cloud Formation and Evolution

Filaments and striations: anisotropies in observed, supersonic, highly magnetized turbulent clouds

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