Aspect Ratio Dependence of the Free-Fall Time for Non-Spherical Symmetries

Pon, Andy; Toalá, J. A.; Johnstone, Doug; Vázquez‐Semadeni, Enrique; Heitsch, Fabian; Gómez, Gilberto C.

doi:10.1088/0004-637x/756/2/145

Cited by 111 publications

(165 citation statements)

References 54 publications

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“…The variation in evolutionary age between the two regions may be due to the more localized mass concentration in the Cocoon Nebula, suggesting a higher initial density leading to a faster collapse. Alternatively, it might simply be due to the known enhanced gravitational instability produced at the ends of cylindrical structures (Pon et al 2011(Pon et al , 2012, assuming that the entire IC 5146 might have begun as a single, elongated entity.…”

Section: Discussionmentioning

confidence: 99%

“…Recently, Pon et al (2011Pon et al ( , 2012 showed that filamentary geometry at this scale is the most favorable scenario in which isothermal perturbations grow before global collapse overwhelms the region dynamics, with the filamentary ends most likely to collapse first. In some numerical simulations, nearly all cores that are detected are associated with filaments and most of these eventually form protostars (e.g., Mairs et al 2014).…”

Section: The Northern Streamermentioning

confidence: 99%

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Alma Resolves the Torus of NGC 1068: Continuum and Molecular Line Emission

García‐Burillo

Combes

Almeida

et al. 2016

ApJL

225

235

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We present 450 and 850 μm submillimeter continuum observations of the IC 5146 star-forming region taken as part of the James Clerk Maxwell Telescope Gould Belt Survey. We investigate the location of bright submillimeter (clumped) emission with the larger-scale molecular cloud through comparison with extinction maps, and find that these denser structures correlate with higher cloud column density. Ninety-six individual submillimeter clumps are identified using FellWalker,and their physical properties are examined. These clumps are found to be relatively massive, ranging from 0.5  M to 116  M with a mean mass of 8  M and a median mass of 3.7  M . A stability analysis for the clumps suggests that the majority are (thermally) Jeans stable, withWe further compare the locations of known protostars with the observed submillimeter emission, finding that younger protostars, i.e., Class 0 and I sources, are strongly correlated with submillimeter peaks and that the clumps with protostars are among the most Jeans unstable. Finally, we contrast the evolutionary conditions in the two major star-forming regions within IC 5146: the young cluster associated with the Cocoon Nebula and the more distributed star formation associated with the Northern Streamer filaments. The Cocoon Nebula appears to have converted a higher fraction of its mass into dense clumps and protostars, the clumps are more likely to be Jeans unstable, and a larger fraction of these remaining clumps contain embedded protostars. The Northern Streamer, however, has a larger number of clumps in total and a larger fraction of the known protostars are still embedded within these clumps.

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Section: Discussionmentioning

confidence: 99%

Section: The Northern Streamermentioning

confidence: 99%

Alma Resolves the Torus of NGC 1068: Continuum and Molecular Line Emission

García‐Burillo

Combes

Almeida

et al. 2016

ApJL

225

235

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“…We can therefore potentially constrain the age of a filament by measuring its velocity gradient. Pon et al (2012) showed that the collapse time of free-falling filaments is τ 1D = √ 2/3 A τ 3D where τ 3D is the spherical free fall time at the same volume density, and A is the aspect ratio of the filament. This equation shows that the collapsing time of a filament can be significantly longer than the standard τ 3D .…”

Section: Dynamical Evolution Scenariosmentioning

confidence: 99%

SDC13 infrared dark clouds: Longitudinally collapsing filaments?

Peretto

Fuller

André

et al. 2014

A&A

198

247

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Formation of stars is now believed to be tightly linked to the dynamical evolution of interstellar filaments in which they form. In this paper we analyze the density structure and kinematics of a small network of infrared dark filaments, SDC13, observed in both dust continuum and molecular line emission with the IRAM 30 m telescope. These observations reveal the presence of 18 compact sources amongst which the two most massive, MM1 and MM2, are located at the intersection point of the parsec-long filaments. The dense gas velocity and velocity dispersion observed along these filaments show smooth, strongly correlated, gradients. We discuss the origin of the SDC13 velocity field in the context of filament longitudinal collapse. We show that the collapse timescale of the SDC13 filaments (from 1 Myr to 4 Myr depending on the model parameters) is consistent with the presence of Class I sources in them, and argue that, on top of bringing more material to the centre of the system, collapse could generate additional kinematic support against local fragmentation, helping the formation of starless super-Jeans cores.

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“…Ostriker 1964;Inutsuka & Miyama 1992;Fischera & Martin 2012;Pon, Johnstone & Heitsch 2011;Pon et al 2012;Heitsch 2013). Magnetic fields have generally been found to have a positive effect on filament stability (Nagasawa 1987;Fiege & Pudritz 2000;Heitsch 2013;Tomisaka 2014).…”

Section: Properties Of Filamentsmentioning

confidence: 99%

Magnetohydrodynamical simulation of the formation of clumps and filaments in quiescent diffuse medium by thermal instability

Wareing

Pittard

Falle

et al. 2016

Mon. Not. R. Astron. Soc.

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We have used the AMR hydrodynamic code, MG, to perform idealised 3D MHD simulations of the formation of clumpy and filamentary structure in a thermally unstable medium without turbulence. A stationary thermally unstable spherical diffuse atomic cloud with uniform density in pressure equilibrium with low density surroundings was seeded with random density variations and allowed to evolve. A range of magnetic field strengths threading the cloud have been explored, from β = 0.1 to β = 1.0 to the zero magnetic field case (β = ∞), where β is the ratio of thermal pressure to magnetic pressure. Once the density inhomogeneities had developed to the point where gravity started to become important, self-gravity was introduced to the simulation. With no magnetic field, clouds and clumps form within the cloud with aspect ratios of around unity, whereas in the presence of a relatively strong field (β = 0.1) these become filaments, then evolve into interconnected corrugated sheets that are predominantly perpendicular to the magnetic field. With magnetic and thermal pressure equality (β = 1.0), filaments, clouds and clumps are formed. At any particular instant, the projection of the 3D structure onto a plane parallel to the magnetic field, i.e. a line of sight perpendicular to the magnetic field, resembles the appearance of filamentary molecular clouds. The filament densities, widths, velocity dispersions and temperatures resemble those observed in molecular clouds. In contrast, in the strong field case β = 0.1, projection of the 3D structure along a line of sight parallel to the magnetic field reveals a remarkably uniform structure.

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Aspect Ratio Dependence of the Free-Fall Time for Non-Spherical Symmetries

Cited by 111 publications

References 54 publications

Alma Resolves the Torus of NGC 1068: Continuum and Molecular Line Emission

Alma Resolves the Torus of NGC 1068: Continuum and Molecular Line Emission

SDC13 infrared dark clouds: Longitudinally collapsing filaments?

Magnetohydrodynamical simulation of the formation of clumps and filaments in quiescent diffuse medium by thermal instability

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