On the effective turbulence driving mode of molecular clouds formed in disc galaxies

Jin, Keitaro; Salim, Diane M.; Federrath, Christoph; Tasker, Elizabeth J.; Habe, Asao; Kainulainen, J.

doi:10.1093/mnras/stx737

Cited by 40 publications

(21 citation statements)

References 77 publications

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“…This is consistent with the emerging picture from global simulations of molecular cloud formation in spiral structures (e.g. Jin et al 2017), where molecular cloud turbulence parameters assume a spectrum of values depending on the details of their shock ingress/egress. Figure 7 shows the velocity dispersion in all three coordinates for MHD runs without self-gravity.…”

Section: Pure Hydrodynamic Runssupporting

confidence: 89%

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: Pure Hydrodynamic Runssupporting

confidence: 89%

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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“…The value of b is important, as the flow dynamics, density structure and the subsequent star formation rate depend on it (Federrath et al 2008;Federrath et al 2010a;Price et al 2011;Konstandin et al 2012;Padoan et al 2014;Federrath & Banerjee 2015;Nolan et al 2015); with compressive driving resulting in broader density probability distribution functions (PDFs) and star formation rates approximately an order of magnitude larger than for solenoidal driving Federrath et al 2016;Federrath 2018). The values of b have been studied systematically for different driving sources of turbulence in numerical simulations (Pan et al 2016;Körtgen et al 2017;Jin et al 2017), and observations also find a significant variation in b across different clouds in the Milky Way (Padoan et al 1997;Brunt 2010;Ginsburg et al 2013;Kainulainen, J. et al 2013;Federrath et al 2016;.…”

Section: Introductionmentioning

confidence: 99%

On the turbulence driving mode of expanding H ii regions

Menon

Federrath

Kuiper

2020

Monthly Notices of the Royal Astronomical Society

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We investigate the turbulence driving mode of ionizing radiation from massive stars on the surrounding interstellar medium (ISM). We run hydrodynamical simulations of a turbulent cloud impinged by a plane-parallel ionization front. We find that the ionizing radiation forms pillars of neutral gas reminiscent of those seen in observations. We quantify the driving mode of the turbulence in the neutral gas by calculating the driving parameter b, which is characterised by the relation σ 2 s = ln(1 + b 2 M 2 ) between the variance of the logarithmic density contrast σ 2 s (where s = ln(ρ/ρ 0 ) with the gas density ρ and its average ρ 0 ), and the turbulent Mach number M. Previous works have shown that b ∼ 1/3 indicates solenoidal (divergence-free) driving and b ∼ 1 indicates compressive (curl-free) driving, with b ∼ 1 producing up to ten times higher star formation rates than b ∼ 1/3. The time variation of b in our study allows us to infer that ionizing radiation is inherently a compressive turbulence driving source, with a time-averaged b ∼ 0.76 ± 0.08. We also investigate the value of b of the pillars, where star formation is expected to occur, and find that the pillars are characterised by a natural mixture of both solenoidal and compressive turbulent modes (b ∼ 0.4) when they form, and later evolve into a more compressive turbulent state with b ∼ 0.5-0.6. A virial parameter analysis of the pillar regions supports this conclusion. This indicates that ionizing radiation from massive stars may be able to trigger star formation by producing predominately compressive turbulent gas in the pillars.

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“…Meanwhile, numerical simulations of molecular cloud formation in disc galaxies and idealised colliding flow setups predict a range of b values emerging in different cloud environments and at different times (Jin et al 2017;Körtgen et al 2017). These studies suggest that a single constant b value cannot be used to describe the turbulence driving of all clouds, but instead that b can vary significantly from cloud to cloud, covering the full range from solenoidal to compressive driving.…”

Section: Introductionmentioning

confidence: 99%

Relationship between turbulence energy and density variance in the solar neighbourhood molecular clouds

Kainulainen

Federrath

2017

A&A

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The relationship between turbulence energy and gas density variance is a fundamental prediction for turbulence-dominated media and is commonly used in analytic models of star formation. We determine this relationship for 15 molecular clouds in the solar neighbourhood. We use the line widths of the CO molecule as the probe of the turbulence energy (sonic Mach number, M s ) and threedimensional models to reconstruct the density probability distribution function (ρ-PDF) of the clouds, derived using near-infrared extinction and Herschel dust emission data, as the probe of the density variance (σ s ). We find no significant correlation between M s and σ s among the studied clouds, but we cannot rule out a weak correlation either. In the context of turbulence-dominated gas, the range of the M s and σ s values corresponds to the model predictions. The data cannot constrain whether the turbulence-driving parameter, b, and/or thermal-to-magnetic pressure ratio, β, vary among the sample clouds. Most clouds are not in agreement with field strengths stronger than given by β 0.05. A model with b 2 β/(β + 1) = 0.30 ± 0.06 provides an adequate fit to the cloud sample as a whole. Based on the average behaviour of the sample, we can rule out three regimes: (i) strong compression combined with a weak magnetic field (b 0.7 and β 3); (ii) weak compression (b 0.35); and (iii) a strong magnetic field (β 0.1). When we include independent magnetic field strength estimates in the analysis, the data rule out solenoidal driving (b < 0.4) for the majority of the solar neighbourhood clouds. However, most clouds have b parameters larger than unity, which indicates a discrepancy with the turbulence-dominated picture; we discuss the possible reasons for this.

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On the effective turbulence driving mode of molecular clouds formed in disc galaxies

Cited by 40 publications

References 77 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

On the turbulence driving mode of expanding H ii regions

Relationship between turbulence energy and density variance in the solar neighbourhood molecular clouds

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