Investigating the global collapse of filaments using smoothed particle hydrodynamics

Clarke, S. D.; Whitworth, Anthony Peter

doi:10.1093/mnras/stv393

Cited by 67 publications

(82 citation statements)

References 14 publications

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“…at the side towards the centre, the gas is accelerated outwards in the direction of the clump, in agreement with the findings of Clarke & Whitworth (2015). Considering the inner parts of the filament, no further fragmentation occurs.…”

Section: Time Evolutionsupporting

confidence: 90%

“…Bastien et al 1991;Bonnell et al 1992;Tomisaka 1995). More recently, Burkert & Hartmann (2004) report the formation of prominent clumps forming at the edge of elongated, collapsing structures (see also Clarke & Whitworth 2015). On molecular cloud scales, the formation of star forming filaments has been studied by means of turbulent box simulations and colliding flows (e.g.…”

Section: Introductionmentioning

confidence: 99%

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The impact of turbulence and magnetic field orientation on star-forming filaments

Seifried

Walch

2015

Mon. Not. R. Astron. Soc.

118

117

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We present simulations of collapsing filaments studying the impact of turbulence and magnetic field morphologies on their evolution and star formation properties. We vary the mass per unit length of the filaments as well as the orientation of the magnetic field with respect to the major axis. We find that the filaments, which have no or a perpendicular magnetic field, typically reveal a smaller width than the universal width of 0.1 pc proposed by e.g. Arzoumanian et al. (2011). We show that this also holds in the presence of supersonic turbulence and that accretion driven turbulence is too weak to stabilize the filaments along their radial direction. On the other hand, we find that a magnetic field that is parallel to the major axis can stabilize the filament against radial collapse resulting in widths of 0.1 pc. Furthermore, depending on the filament mass and magnetic field configuration, gravitational collapse and fragmentation in filaments occurs either in an edge-on way, uniformly distributed across the entire length, or in a mixed way. In the presence of initially moderate density perturbations, a centralized collapse towards a common gravitational centre occurs. Our simulations can thus reproduce different modes of fragmentation observed recently in star forming filaments. Moreover, we find that turbulent motions influence the distance between individual fragments along the filament, which does not always match the results of a Jeans analysis.

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Section: Time Evolutionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

The impact of turbulence and magnetic field orientation on star-forming filaments

Seifried

Walch

2015

Mon. Not. R. Astron. Soc.

118

117

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“…5 and 6) suggest that the local collapse might occur a factor of two-to-three faster at the ends of the filament than at its center. Similarly, Clarke & Whitworth (2015) found in their numerical simulations that the first fragments form at the ends of the filament, regardless of its aspect ratio. While there are some quantitative differences between the predictions of Clarke & Whitworth (2015) and Pon et al (2011Pon et al ( , 2012, both models predict that long (but finitesized) filaments fragment starting from the ends of the cloud.…”

Section: Musca: Caught In the Middle Of Gravitational Fragmentationmentioning

confidence: 68%

“…One possible mechanism in the context of gravitational fragmentation is provided by finite-size effects in cylindric geometry (as opposed to the infinite models of Ostriker 1964;and Fischera & Martin 2012a). In finite filaments, the acceleration of gas depends on the relative position along the filament, which is largest at its ends (Bastien 1983;Pon et al 2011Pon et al , 2012Clarke & Whitworth 2015, see also Burkert & Hartmann 2004, for a study in a sheet geometry). These higher accelerations may translate into shorter local collapse timescales, and therefore, into formation of fragments at the ends of the filament prior to its center (Pon et al 2011(Pon et al , 2012.…”

Section: Musca: Caught In the Middle Of Gravitational Fragmentationmentioning

confidence: 99%

Gravitational fragmentation caught in the act: the filamentary Musca molecular cloud

Kainulainen

Hacar

Alves

et al. 2016

A&A

111

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Context. Filamentary structures are common in molecular clouds. Explaining how they fragment to dense cores is a missing step in understanding their role in star formation. Aims. We perform a case study of whether low-mass filaments are close to hydrostatic prior to their fragmentation, and whether their fragmentation agrees with gravitational fragmentation models. To accomplish this, we study the ∼6.5 pc long Musca molecular cloud, which is an ideal candidate for a filament at an early stage of fragmentation. Methods. We employ dust extinction mapping, in conjunction with near-infrared JHK S -band data from the CTIO/NEWFIRM instrument, and 870 μm dust continuum emission data from the APEX/LABOCA instrument to estimate column densities in Musca. We use the data to identify fragments from the cloud and to determine the radial density distribution of its filamentary part. We compare the cloud's morphology with 13 CO and C 18 O line emission observed with the APEX/SHeFI instrument. Results. The Musca cloud is pronouncedly fragmented at its ends, but harbors a remarkably well-defined, ∼1.6 pc long filament in its center region. The line mass of the filament is 21-31 M pc −1 and the full width at half maximum (FWHM) 0.07 pc. The radial profile of the filament can be fitted with a Plummer profile, which has the power-index of 2.6 ± 11% and is flatter than that of an infinite hydrostatic filament. The profile can also be fitted with a hydrostatic cylinder truncated by external pressure. These models imply a central density of ∼5-10 × 10 4 cm −3 . The fragments in the cloud have a mean separation of ∼0.4 pc, in agreement with gravitational fragmentation. These properties, together with the subsonic and velocity-coherent nature of the cloud, suggest a scenario in which an initially hydrostatic cloud is currently gravitationally fragmenting. The fragmentation started a few tenths of a Myr ago from the ends of the cloud, leaving its center still relatively nonfragmented, possibly because of gravitational focusing in a finite geometry.

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“…However, this is not an appropriate approach for nonspherical objects like the high-aspect ratio filamentary structures within SDC13 (Pon et al 2012;Toalá et al 2012). Clarke & Whitworth (2015) derive a collapse timescale (t col ) valid for both filamentary and near spherical structures:…”

Section: Collapse Timescalesmentioning

confidence: 99%

Gravity drives the evolution of infrared dark hubs: JVLA observations of SDC13

Williams

Peretto

Avison

et al. 2018

A&A

112

110

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Context. Converging networks of interstellar filaments, i.e. hubs, have been recently linked to the formation of stellar clusters and massive stars. Understanding the relationship between the evolution of these systems and the formation of cores/stars inside them is at the heart of current star formation research. Aims. The goal is to study the kinematic and density structure of the SDC13 prototypical hub at high angular resolution to determine what drives its evolution and fragmentation. Methods. We have mapped SDC13, a ∼1000 M infrared dark hub, in NH 3 (1,1) and NH 3 (2,2) emission lines, with both the Jansky Very Large Array and Green Bank Telescope. The high angular resolution achieved in the combined dataset allowed us to probe scales down to 0.07pc. After fitting the ammonia lines, we computed the integrated intensities, centroid velocities and line widths, along with gas temperatures and H 2 column densities. Results. The mass-per-unit-lengths of all four hub filaments are thermally super-critical, consistent with the presence of tens of gravitationally bound cores identified along them. These cores exhibit a regular separation of ∼ 0.37 ± 0.16 pc suggesting gravitational instabilities running along these super-critical filaments are responsible for their fragmentation. The observed local increase of the dense gas velocity dispersion towards starless cores is believed to be a consequence of such fragmentation process. Using energy conservation arguments, we estimate that the gravitational to kinetic energy conversion efficiency in the SDC13 cores is ∼ 35%. We see velocity gradient peaks towards ∼ 63% of the cores as expected during the early stages of filament fragmentation. Another clear observational signature is the presence of the most massive cores at the filaments' junction, where the velocity dispersion is the largest. We interpret this as the result of the hub morphology generating the largest acceleration gradients near the hub centre. Conclusions. We propose a scenario for the evolution of the SDC13 hub in which filaments first form as post-shock structures in a supersonic turbulent flow. As a result of the turbulent energy dissipation in the shock, the dense gas within the filaments is initially mostly sub-sonic. Then gravity takes over and starts shaping the evolution of the hub, both fragmenting filaments and pulling the gas towards the centre of the gravitational well. By doing so, gravitational energy is converted into kinetic energy in both local (cores) and global (hub centre) potential well minima. Furthermore, the generation of larger gravitational acceleration gradients at the filament junctions promotes the formation of more massive cores.

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Investigating the global collapse of filaments using smoothed particle hydrodynamics

Cited by 67 publications

References 14 publications

The impact of turbulence and magnetic field orientation on star-forming filaments

The impact of turbulence and magnetic field orientation on star-forming filaments

Gravitational fragmentation caught in the act: the filamentary Musca molecular cloud

Gravity drives the evolution of infrared dark hubs: JVLA observations of SDC13

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