Fractal Dimension of Interstellar Clouds: Opacity and Noise Effects

Sánchez, Néstor; Alfaro, E. J.; Pérez, E.

doi:10.1086/510351

Cited by 35 publications

(49 citation statements)

References 15 publications

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“…As found in previous observational studies (e.g., Roman-Duval et al 2010), the cloud surface density increases with increasing cloud size, in agreement with estimates of MC fractal dimensions from various observational surveys (e.g., Bazell & Desert 1988;Zimmermann & Stutzki 1992;Elmegreen & Falgarone 1996;Sánchez et al 2007) and from simulations of randomly driven turbulence (e.g., Kritsuk et al 2007;Federrath et al 2009). This trend is reproduced by our fiducial synthetic catalog, though with a slightly shallower slope than in the Outer Galaxy Survey.…”

Section: Mass and Size Distributionssupporting

confidence: 90%

Supernova Driving. Iii. Synthetic Molecular Cloud Observations

Padoan

Juvela

Pan

et al. 2016

ApJ

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We present a comparison of molecular clouds (MCs) from a simulation of supernova (SN) driven interstellar medium (ISM) turbulence with real MCs from the Outer Galaxy Survey. The radiative transfer calculations to compute synthetic CO spectra are carried out assuming that the CO relative abundance depends only on gas density, according to four different models. Synthetic MCs are selected above a threshold brightness temperature value, T B,min = 1.4 K, of the J = 1 − 0 12 CO line, generating 16 synthetic catalogs (four different spatial resolutions and four CO abundance models), each containing up to several thousands MCs. The comparison with the observations focuses on the mass and size distributions and on the velocity-size and mass-size Larson relations. The mass and size distributions are found to be consistent with the observations, with no significant variations with spatial resolution or chemical model, except in the case of the unrealistic model with constant CO abundance. The velocity-size relation is slightly too steep for some of the models, while the mass-size relation is a bit too shallow for all models only at a spatial resolution dx ≈ 1 pc. The normalizations of the Larson relations show a clear dependence on spatial resolution, for both the synthetic and the real MCs. The comparison of the velocity-size normalization suggests that the SN rate in the Perseus arm is approximately 70% or less of the rate adopted in the simulation. Overall, the realistic properties of the synthetic clouds confirm that SN-driven turbulence can explain the origin and dynamics of MCs.

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Section: Mass and Size Distributionssupporting

confidence: 90%

Supernova Driving. Iii. Synthetic Molecular Cloud Observations

Padoan

Juvela

Pan

et al. 2016

ApJ

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“…The proposed range for the fractal dimension is also in agreement with observations (e.g. Elmegreen & Falgarone 1996;Sánchez et al 2007, and references therein) and simulations suggesting an overall fractal dimension of interstellar clouds in the range D ≈ 2.0 − 2.7.…”

Section: The Fractal Dimensionsupporting

confidence: 90%

Mach number study of supersonic turbulence: the properties of the density field

Konstandin

Schmidt

Girichidis

et al. 2016

Mon. Not. R. Astron. Soc.

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We model driven, compressible, isothermal, turbulence with Mach numbers ranging from the subsonic (M ≈ 0.65) to the highly supersonic regime (M ≈ 16). The forcing scheme consists both solenoidal (transverse) and compressive (longitudinal) modes in equal parts. We find a relation σ 2 s = b log (1 + b 2 M 2 ) between the Mach number and the standard deviation of the logarithmic density with b = 0.457 ± 0.007. The density spectra follow D(k, M) ∝ k ζ(M) with scaling exponents depending on the Mach number. We find ζ(M) = αM β with a coefficient α that varies slightly with resolution, whereas β changes systematically. We extrapolate to the limit of infinite resolution and find α = −1.91 ± 0.01, β = −0.30 ± 0.03. The dependence of the scaling exponent on the Mach number implies a fractal dimension D = 2 + 0.96M −0.30 . We determine how the scaling parameters depend on the wavenumber and find that the density spectra are slightly curved. This curvature gets more pronounced with increasing Mach number. We propose a physically motivated fitting formula D(k) = D 0 k ζk η by using simple scaling arguments. The fit reproduces the spectral behaviour down to scales k ≈ 80. The density spectrum follows a single power-law η = −0.005 ± 0.01 in the low Mach number regime and the strongest curvature η = −0.04 ± 0.02 for the highest Mach number. These values of η represent a lower limit, as the curvature increases with resolution.

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“…and the total scatter, we can conclude that the mass-size relation resulting from SN-driven turbulence is consistent with that of real MCs from the Outer Galaxy Survey. A similar mass-size relation (though with a five times larger normalization) was also derived from the Galactic Ring Survey (Roman-Duval et al 2010) and is implied by previous estimates of cloud fractal dimensions from various observational surveys (e.g., Elmegreen & Falgarone 1996;Sánchez et al 2007) and from simulations of randomly driven turbulence (e.g., Kritsuk et al 2007;Federrath et al 2009). …”

Section: Mass-size Relationsupporting

confidence: 78%

Supernova Driving. I. The Origin of Molecular Cloud Turbulence

Padoan

Pan

Haugbølle

et al. 2016

ApJ

217

230

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Turbulence is ubiquitous in molecular clouds (MCs), but its origin is still unclear because MCs are usually assumed to live longer than the turbulence dissipation time. Interstellar medium (ISM) turbulence is likely driven by supernova (SN) explosions, but it has never been demonstrated that SN explosions can establish and maintain a turbulent cascade inside MCs consistent with the observations. In this work, we carry out a simulation of SNdriven turbulence in a volume of (250 pc) 3 , specifically designed to test if SN driving alone can be responsible for the observed turbulence inside MCs. We find that SN driving establishes a velocity scaling consistent with the usual scaling laws of supersonic turbulence, suggesting that previous idealized simulations of MC turbulence, driven with a random, large-scale volume force, were correctly adopted as appropriate models for MC turbulence, despite the artificial driving. We also find that the same scaling laws extend to the interiors of MCs, and that the velocity-size relation of the MCs selected from our simulation is consistent with that of MCs from the OuterGalaxy Survey, the largest MC sample available. The mass-size relation and the mass and size probability distributions also compare successfully with those of the Outer Galaxy Survey. Finally, we show that MC turbulence is super-Alfvénic with respect to both the mean and rms magnetic-field strength. We conclude that MC structure and dynamics are the natural result of SN-driven turbulence.

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Fractal Dimension of Interstellar Clouds: Opacity and Noise Effects

Cited by 35 publications

References 15 publications

Supernova Driving. Iii. Synthetic Molecular Cloud Observations

Supernova Driving. Iii. Synthetic Molecular Cloud Observations

Mach number study of supersonic turbulence: the properties of the density field

Supernova Driving. I. The Origin of Molecular Cloud Turbulence

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