Energy Budget of Forming Clumps in Numerical Simulations of Collapsing Clouds

Camacho, Vianey; Vázquez‐Semadeni, Enrique; Ballesteros-Paredes, Javier; Gómez, Gilberto C.; Fall, S. Michael; Mata-Chávez, M. Dolores

doi:10.3847/1538-4357/833/1/113

Cited by 40 publications

(58 citation statements)

References 83 publications

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“…DISCUSSION 7.1. Implications for Timescales Encouragingly, numerical simulations of star-forming molecular clumps, but without radiative transfer (Padoan et al 2016;Camacho et al 2016, and earlier work referenced therein), show distinct signs of contraction and dispersal in the 3D velocity field, and in a similar ratio of about half the clumps contracting and half dispersing, as in our derived mass flux maps (Fig. 14).…”

Section: Mass Dispersalsupporting

confidence: 79%

The Galactic Census of High- and Medium-mass Protostars. IV. Molecular Clump Radiative Transfer, Mass Distributions, Kinematics, and Dynamical Evolution

Barnes

Hernandez²,

Müller

et al. 2018

ApJ

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We present 12 CO, 13 CO, & C 18 O data as the next major release for the CHaMP project, an unbiased sample of Galactic molecular clouds in l = 280 • -300 • . From a radiative transfer analysis, we selfconsistently compute 3D cubes of optical depth, excitation temperature, and column density for ∼300 massive clumps, and update the I12 CO -dependent CO→H 2 conversion law of Barnes et al. (2015). For N ∝ I p , we find p = 1.92±0.05 for the velocity-resolved conversion law aggregated over all clumps. A practical, integrated conversion law is N12 CO = (4.0±0.3)×10 19 m −2 I12 CO 1.27±0.02 , confirming an overall 2× higher total molecular mass for Milky Way clouds, compared to the standard X factor.We use these laws to compare the kinematics of clump interiors with their foreground 12 CO envelopes, and find evidence that most clumps are not dynamically uniform: irregular portions seem to be either slowly accreting onto the interiors, or dispersing from them. We compute the spatiallyresolved mass accretion/dispersal rate across all clumps, and map the local flow timescale. While these flows are not clearly correlated with clump structures, the inferred accretion rate is a statistically strong function of the local mass surface density Σ, suggesting near-exponential growth or loss of mass over effective timescales ∼30-50 Myr. At high enough Σ, accretion dominates, suggesting gravity plays an important role in both processes. If confirmed by numerical simulations, this sedimentation picture would support arguments for long clump lifetimes mediated by pressure confinement, with a terminal crescendo of star formation, suggesting a resolution to the 40-yr-old puzzle of the dynamical state of molecular clouds and their low star formation efficiency.

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Section: Mass Dispersalsupporting

confidence: 79%

The Galactic Census of High- and Medium-mass Protostars. IV. Molecular Clump Radiative Transfer, Mass Distributions, Kinematics, and Dynamical Evolution

Barnes

Hernandez²,

Müller

et al. 2018

ApJ

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“…1 of Ballesteros-Paredes et al (2011), where the authors plot observed cores from different regions on the same axes. Large spreads in velocity dispersions in pre-stellar cores due to a dependence on surface density have also been reported in theoretical work (Ballesteros-Paredes & Mac Low 2002;Camacho et al 2016). However, the cores in this study are drawn from environments of similar surface density.…”

Section: Kinematic and Mass-size Relationssupporting

confidence: 67%

Core and stellar mass functions in massive collapsing filaments

Ntormousi

Hennebelle

2019

A&A

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Context. The connection between the pre-stellar core mass function (CMF) and the stellar initial mass function (IMF) lies at the heart of all star formation theories, but it is inherently observationally unreachable. Aims. In this paper we aim to elucidate the earliest phases of star formation with a series of high-resolution numerical simulations that include the formation of sinks from high-density clumps. In particular, we focus on the transition from cores to sink particles within a massive molecular filament, and work towards identifying the factors that determine the shape of the CMF and the IMF. Methods. We compare the CMF and IMF between magnetized and unmagnetized simulations, and between different resolutions. In order to study the effect of core stability, we apply different selection criteria according to the virial parameter and the mass-to-flux ratio of the cores. Results. We find that, in all models, selecting cores based on their kinematic virial parameter tends to exclude collapsing objects, because they host high velocity dispersions. Selecting only the thermally unstable magnetized cores, we observe that their mass-to-flux ratio spans almost two orders of magnitude for a given mass. We also see that, when magnetic fields are included, the CMF peaks at higher core mass values with respect to a pure hydrodynamical simulation. Nonetheless, all models produce sink mass functions with a high-mass slope consistent with Salpeter. Finally, we examine the effects of resolution and find that, in these isothermal simulations, even models with very high dynamical range fail to converge in the mass function. Conclusions. Our main conclusion is that, although the resulting CMFs and IMFs have similar slopes in all simulations, the cores have slightly different sizes and kinematical properties when a magnetic field is included, and this affects their gravitational stability. Nonetheless, a core selection based on the mass-to-flux ratio is not enough to alter the shape of the CMF, if we do not take thermal stability into account. Finally, we conclude that extreme care should be given to resolution issues when studying sink formation with an isothermal equation of state, since with each increase in resolution, fragmentation continues to smaller scales in a self-similar way.

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“…We explore the possibility that non-thermal motions observed in the sample are originated by global gravitational collapse (e.g., Ballesteros-Paredes et al 2011;Camacho et al 2016). In this scenario, gravitational energy is released during the hierarchical collapse of clouds and clumps, increasing the kinetic energy and driving nonthermal motions in regions of overdensity.…”

Section: Non-thermal Motions Driven By Gravitational Collapsementioning

confidence: 99%

Thermal balance and comparison of gas and dust properties of dense clumps in the Hi-GAL survey

Merello

Molinari

Rygl

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We present a comparative study of physical properties derived from gas and dust emission in a sample of 1068 dense Galactic clumps. The sources are selected from the crossmatch of the Hi-GAL survey with 16 catalogues of NH 3 line emission in its lowest inversion (1,1) and (2,2) transitions. The sample covers a large range in masses and bolometric luminosities, with surface densities above Σ = 0.1 g cm −2 and with low virial parameters α < 1. The comparison between dust and gas properties shows an overall agreement between T kin and T dust at volumetric densities n 1.2 × 10 4 cm −3 , and a median fractional abundance χ(NH 3 )= 1.46 × 10 −8 . While the protostellar clumps in the sample have small differences between T kin and T dust , prestellar clumps have a median ratio T kin /T dust = 1.24, suggesting that these sources are thermally decoupled. A correlation is found between the evolutionary tracer L/M and the parameters T kin /T dust and χ(NH 3 ) in prestellar sources and protostellar clumps with L/M < 1 L ⊙ M ⊙ −1 . In addition, a weak correlation is found between non-thermal velocity dispersion and the L/M parameter, possibly indicating an increase of turbulence with protostellar evolution in the interior of clumps. Finally, different processes are discussed to explain the differences between gas and dust temperatures in prestellar candidates, and the origin of non-thermal motions observed in the clumps.

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Energy Budget of Forming Clumps in Numerical Simulations of Collapsing Clouds

Cited by 40 publications

References 83 publications

The Galactic Census of High- and Medium-mass Protostars. IV. Molecular Clump Radiative Transfer, Mass Distributions, Kinematics, and Dynamical Evolution

The Galactic Census of High- and Medium-mass Protostars. IV. Molecular Clump Radiative Transfer, Mass Distributions, Kinematics, and Dynamical Evolution

Core and stellar mass functions in massive collapsing filaments

Thermal balance and comparison of gas and dust properties of dense clumps in the Hi-GAL survey

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