Giant molecular cloud collisions as triggers of star formation. VI. Collision-induced turbulence

Wu, Benjamin; Tan, Jonathan C.; Nakamura, Fúmitaka; Christie, Duncan; Li, Qi

doi:10.1093/pasj/psx140

Cited by 25 publications

(27 citation statements)

References 59 publications

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“…self-gravity will dominate over MHD effects (Crutcher 2012). Our results are in good agreement with simulations of turbulence generation through supercritical molecular cloud collisions, where clumpy structures in the collision act as efficient injectors of turbulent momentum (Wu et al 2018).…”

Section: Mhd Runs With Self-gravitysupporting

confidence: 84%

Clumpy shocks as the driver of velocity dispersion in molecular clouds: the effects of self-gravity and magnetic fields

Forgan

Bonnell

2018

Monthly Notices of the Royal Astronomical Society

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We revisit an alternate explanation for the turbulent nature of molecular cloudsnamely, that velocity dispersions matching classical predictions of driven turbulence can be generated by the passage of clumpy material through a shock. While previous work suggested this mechanism can reproduce the observed Larson relation between velocity dispersion and size scale (σ ∝ L Γ with Γ ≈ 0.5), the effects of self-gravity and magnetic fields were not considered. We run a series of smoothed particle magnetohydrodynamics experiments, passing clumpy gas through a shock in the presence of a combination of self-gravity and magnetic fields. We find powerlaw relations between σ and L throughout, with indices ranging from Γ = 0.3 − 1.2. These results are relatively insensitive to the strength and geometry of magnetic fields, provided that the shock is relatively strong. Γ is strongly sensitive to the angle between the gas' bulk velocity and the shock front, and the shock strength (compared to the gravitational boundness of the pre-shock gas). If the origin of the σ − L relation is in clumpy shocks, deviations from the standard Larson relation constrain the strength and behaviour of shocks in spiral galaxies.

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Section: Mhd Runs With Self-gravitysupporting

confidence: 84%

Clumpy shocks as the driver of velocity dispersion in molecular clouds: the effects of self-gravity and magnetic fields

Forgan

Bonnell

2018

Monthly Notices of the Royal Astronomical Society

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“…However, as their observations do not only focus on the star-forming parts of Orion-B but on the whole region, the median M decreases to 6. In our case, observations were centered on two star-forming regions which explains the higher M. Such high values of M have been observed for instance toward Orion A (González Lobos & Stutz 2019), GMF38a (Wu et al 2018), and quiescent 70 µm clumps (Traficante et al 2018).…”

Section: Estimation Of the Mach Numbersupporting

confidence: 58%

APEX CO observations towards the photodissociation region of RCW 120

Figueira

Zavagno

Bronfman

et al. 2020

A&A

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Context. The edges of ionized (H II) regions are important sites for the formation of (high-mass) stars. Indeed, at least 30% of the Galactic high-mass-star formation is observed there. The radiative and compressive impact of the H II region could induce star formation at the border following different mechanisms such as the collect and collapse or the radiation-driven implosion (RDI) models and change their properties. Aims. We aim to study the properties of two zones located in the photo dissociation region (PDR) of the Galactic H II region RCW 120 and discuss them as a function of the physical conditions and young star contents found in both clumps. Methods. Using the APEX telescope, we mapped two regions of size 1.5′ × 1.5′ toward the most massive clump of RCW 120 hosting young massive sources and toward a clump showing a protrusion inside the H II region and hosting more evolved low-mass sources. The 12CO (J = 3−2), 13CO (J = 3−2) and C18O (J = 3−2) lines observed, together with Herschel data, are used to derive the properties and dynamics of these clumps. We discuss their relation with the hosted star formation. Results. Assuming local thermodynamic equilibrium, the increase of velocity dispersion and Tex are found toward the center of the maps, where star-formation is observed with Herschel. Furthermore, both regions show supersonic Mach numbers (7 and 17 in average). No substantial information has been gathered about the impact of far ultraviolet radiation on C18O photodissociation at the edges of RCW 120. The fragmentation time needed for CC to be at work is equivalent to the dynamical age of RCW 120 and the properties of region B are in agreement with bright-rimmed clouds. Conclusions. Although conclusions from this fragmentation model should be taken with caution, it strengthens the fact that, together with evidence of compression, CC might be at work at the edges of RCW 120. Additionally, the clump located at the eastern part of the PDR is a good candidate pre-existing clump where star-formation may be induced by the RDI mechanism.

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“…This scenario has been theoretically investigated through numerical simulations by a number of authors (e.g. Takahira et al 2014, Balfour et al 2015, Takahira et al 2018, Wu et al 2018, Fukui et al 2021 generally finding that cloud-cloud collisions increase the SFE and boost the birth of high-mass stars. Takahira et al (2018) find a CMF with α = 1.6 in the high-mass end for a low collision speed (5 km s −1 ), which is consistent with our determinations in the active region.…”

Section: The Cmf and Comparison With The Imfmentioning

confidence: 99%

A possible far-ultraviolet flux-dependent core mass function in NGC 6357

Brand,

Giannetti,

Massi

et al. 2021

Preprint

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Context. NGC6357 is a galactic star-forming complex (d ∼ 1.7 kpc) composed of several Hii regions, a few young stellar clusters, and giant molecular clouds. In particular, the Hii regions G353.2+0.9, G353.1+0.6, and G353.2+0.7 are associated with three young clusters; the most prominent of these, Pismis 24, contains some of the most massive stars known. Aims. We aim to derive the properties of the densest compact gas structures (cores) in the region as well as the effects of an intense far-ultraviolet (FUV) radiation field on their global properties. Methods. We mapped the NGC6357 region at 450 and 850 µm with SCUBA-2 and in the CO(3-2) line with HARP at the JCMT. We also made use of the Herschel Hi-GAL data at 70 and 160 µm. We used the algorithm Gaussclumps to retrieve the compact cores embedded in the diffuse sub-millimetre emission and constructed their spectral energy distribution from 70 to 850 µm, from which we derived mass and temperature. We divided the observed area into an 'active' region (i.e. the eastern half, which is exposed to the FUV radiation from the more massive members of the three clusters) and a 'quiescent' region (i.e. the western half, which is less affected by FUV radiation). We compared the core mass functions and the temperature distributions in the two areas to look for any differences that could be due to the different levels of FUV radiation. Results. We retrieved 686 dense cores, 411 in the active region and 275 in the quiescent region, with an estimated mass completeness limit of ∼ 5 M . We also attempted to select a sample of pre-stellar cores based on cross-correlation with 70 µm emission and red WISE point sources, which unfortunately is biased due to distance, emission at 70 µm from the dust on the surface of the cores that is heated by the FUV radiation, and saturation in the WISE bands. Most of the cores above the mass completeness limit are likely to be gravitationally bound. The fraction of gas in dense cores is very low, 1.4 %. We found a mass-size relation log(M/M ) ∼ a × log(D/arcsec), with a in the range 2.0-2.4, depending on the precise selection of the sample. The temperature distributions in the two sub-regions are clearly different, peaking at ∼ 25 K in the quiescent region and at ∼ 35 K in the active region. The core mass functions are different as well, at a 2σ level, consistent with a Salpeter initial mass function in the quiescent region and flatter than that in the active region. The dense cores lying close to the Hii regions are consistent with pre-existing cores being gradually engulfed by a photon dominated region and photoevaporating. A comparison of the obtained distribution of core masses with those derived from simulations of cloud-cloud collisions yields no conclusive evidence of ongoing cloud-cloud collisions. Conclusions. We attribute the different global properties of dense cores in the two sub-regions to the influence of the FUV radiation field.

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Giant molecular cloud collisions as triggers of star formation. VI. Collision-induced turbulence

Cited by 25 publications

References 59 publications

Clumpy shocks as the driver of velocity dispersion in molecular clouds: the effects of self-gravity and magnetic fields

Clumpy shocks as the driver of velocity dispersion in molecular clouds: the effects of self-gravity and magnetic fields

APEX CO observations towards the photodissociation region of RCW 120

A possible far-ultraviolet flux-dependent core mass function in NGC 6357

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