The Universality of Turbulence in Galactic Molecular Clouds

By M. Heyer, C. Brunt. 2004

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The universality of interstellar turbulence is examined from observed structure functions of 27 giant molecular clouds and Monte Carlo modeling. We show that the structure functions, δv = volγ, derived from wide-field imaging of 12CO J=1-0 emission from individual clouds are described by a narrow range in the scaling exponent, γ, and the scaling coefficient, vo. The similarity of turbulent structure functions emphasizes the universality of turbulence in the molecular interstellar medium and accounts for the cloud-to-cloud size/line width relationship initially identified by Larson. The degree of turbulence universality is quantified by Monte Carlo simulations that reproduce the mean squared velocity residuals of the observed cloud-to-cloud relationship. Upper limits to the variation of the scaling amplitudes and exponents for molecular clouds are ~10%-20%. The measured invariance of turbulence for molecular clouds with vastly different sizes, environments, and star formation activity suggests a common formation mechanism such as converging turbulent flows within the diffuse interstellar medium and a limited contribution of energy from sources within the cloud with respect to large-scale driving mechanisms.

Subfields: Astronomy and Astrophysics, Atmospheric Science

View Paper: https://www.semanticscholar.org/paper/1a6ddb6a17cc29dfe9cc482e4130b4de32b7532f

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Citations in the corpus

THE EFFECTS OF RADIATIVE TRANSFER ON LOW-MASS STAR FORMATION (2009, background): “(13) The initial box temperature is T = 10 K, length of the box L = 0.65 pc and the average density is ρ = 4.46 × 10−20 g cm−3, so that the cloud satisfies the observed linewidth-size relation (Solomon et al. 1987; Heyer & Brunt 2004).”
On the universality of supersonic turbulence (2013, neutral): “…turbulent velocity dispersion–size scaling (often referred to as the Larson 1981 relation) of v ∝ 0.5, as measured in observational studies of molecular clouds (Larson 1981; Solomon et al. 1987; Falgarone, Puget & Perault 1992; Ossenkopf & Mac Low 2002; Heyer & Brunt 2004; Roman-Duval et al. 2011).”
The Resolved Properties of Extragalactic Giant Molecular Clouds (2008, background): “Many of the results, however, are reassuringly similar: extragalactic GMCs broadly share the same properties observed in Milky Way GMCs, although the clouds in some galaxies (notably the SMC) appear to be somewhat different from the remainder of the sample.”
ON THE STAR FORMATION EFFICIENCY OF TURBULENT MAGNETIZED CLOUDS (2012, background): “These parameters were chosen to roughly follow observed properties of molecular clouds, covering a range of cloud sizes L ∼ 0.3–200 pc, masses Mc ∼ 300 to 4 × 106M , and velocity dispersions σV ∼ 0.6–10 km s−1 (e.g., Larson 1981; Solomon et al. 1987; Falgarone et al. 1992; Ossenkopf & Mac Low 2002; ”
THE LONG-TERM EVOLUTION OF THE GALACTIC DISK TRACED BY DISSOLVING STAR CLUSTERS (2010, background): “Observations indicate that the turbulent motions in molecular clouds are correlated on the scale of the entire cloud (Heyer & Brunt 2004), so L is roughly the size of a cloud.”
The Global Evolution of Giant Molecular Clouds. I. Model Formulation and Quasi-Equilibrium Behavior (2006, neutral): “We set the initial cloud column density to NH,22 = 1.5, where NH = NH,22×1022 cm−2, which is typical for Milky Way GMCs regardless of mass (Larson 1981; Solomon et al. 1987).”
Slow Star Formation in Dense Gas: Evidence and Implications (2006, background): “…clustering statistics (e.g., Klessen & Burkert 2001; Schmeja & Klessen 2004), the linewidth-size relation of the gas (e.g., Ossenkopf & Mac Low 2002), and the line luminosity of molecular clouds (Heyer & Brunt 2004), suggest that turbulence in molecular clouds is primarily driven on large scales.”
A NEW JEANS RESOLUTION CRITERION FOR (M)HD SIMULATIONS OF SELF-GRAVITATING GAS: APPLICATION TO MAGNETIC FIELD AMPLIFICATION BY GRAVITY-DRIVEN TURBULENCE (2011, background): “Over the last 30 years it has become clear that the turbulence in presentday molecular clouds contains most of the energy on large scales (Larson 1981; Solomon et al. 1987; Ossenkopf & Mac Low 2002; Heyer & Brunt 2004), i.e., it is driven on large scales (Brunt et al. 2009, and references therein).”
THE FRACTAL DENSITY STRUCTURE IN SUPERSONIC ISOTHERMAL TURBULENCE: SOLENOIDAL VERSUS COMPRESSIVE ENERGY INJECTION (2007, background): “…provide velocity dispersion to size relations for various molecular clouds (MCs), which document the existence of supersonic random motions on scales larger than ∼ 0.1 pc (e.g., Larson 1981; Myers 1983; Perault et al. 1986; Solomon et al. 1987; Falgarone et al. 1992; Heyer & Brunt 2004).”
The molecular gas in Luminous Infrared Galaxies I: CO lines, extreme physical conditions, and their drivers (2011, positive): “Using theσv-L (velocity dispersion)-(cloud size) relation σv = σ◦ ( Pe P◦ )1/4 ( L pc )α (14) (Larson 1981), which is now well-established for the Galaxywith nearly constantσ◦=1.2 km s−1 and power-law indexα=1/2 (Heyer & Brunt 2004).”
Cold Dark Clouds: The Initial Conditions for Star Formation (2007, methodology): “Using these and additional data, Heyer & Brunt (2004) have found an almost universal power-law form for the energy spectrum of clouds, with very little cloud-to-cloud scatter (10-20”
Importance of the Initial Conditions for Star Formation - I. Cloud Evolution and Morphology (2010, background): “…and in many cases they show large linewidths, indicating supersonic, turbulent motions with a power-law spectral velocity distribution consistent with P(k) ∝ k−2 (Zuckerman & Evans 1974; Larson 1981; Heyer & Brunt 2004), and thus steeper than the Kolmogorov spectrum of turbulence, P(k) ∝ k−5/3.”
Molecular Clouds in the Milky Way (2015, methodology): “This latter implication is further emphasized by Heyer & Brunt (2004) and Heyer et al. (2006) as their samples include molecular clouds with massive star formation and others with little star-formation activity.”
The “Mysterious” Origin of Brown Dwarfs (2002, background): “The dotted line corresponds to values of rms Mach number and average gas density of typical Larson relations (Larson 1981; Brunt 2003; Heyer & Brunt 2004).”
A General Theory of Turbulence-regulated Star Formation, from Spirals to Ultraluminous Infrared Galaxies (2005, background): “The same is true of molecular clouds with masses P104 M (Heyer & Brunt 2004).”
FORMATION OF MASSIVE MOLECULAR CLOUD CORES BY CLOUD–CLOUD COLLISION (2013, background): “The power spectrum of the density fluctuations is set as an isotropic power law: (logρ)2k k 2 ∝ k−2 (Larson 1981; Heyer & Brunt 2004), which can be expected by supersonic turbulence that follows Larson’s law (Beresnyak et al. 2005, see also, Elmegreen & Scalo 2004; Scalo & Elmegreen 2004).”
MODELING COLLAPSE AND ACCRETION IN TURBULENT GAS CLOUDS: IMPLEMENTATION AND COMPARISON OF SINK PARTICLES IN AMR AND SPH (2010, background): “…cells with a velocity power spectrum P (k) ∝ k−4, consistent with the observed velocity dispersionsize relation in molecular clouds (e.g., Larson 1981; Heyer & Brunt 2004), and consistent with the velocity spectra usually obtained for driven supersonic turbulence (e.g., Federrath et al. 2009a;…”
Inefficient star formation through turbulence, magnetic fields and feedback (2015, background): “A third alternative is that the observed supersonic random motions (Zuckerman & Palmer 1974; Zuckerman & Evans 1974; Larson 1981; Solomon et al. 1987; Falgarone et al. 1992; Ossenkopf & Mac Low 2002; Heyer & Brunt 2004; Schneider et al. 2011; Roman-Duval et al. 2011) regulate star formation.”
Global hierarchical collapse in molecular clouds. Towards a comprehensive scenario (2019, background): “…et al. 2005; Vázquez-Semadeni et al. 2006, 2007, 2010; Wareing et al. 2019) is only moderately supersonic (Mach numbers Ms ∼ 3) with respect to the dense, cold gas, in contrast with the highly supersonic regimes (Ms & 10) indicated by observations of MCs (e.g., Larson 1981; Heyer & Brunt 2004).”