How do velocity structure functions trace gas dynamics in simulated molecular clouds?

Abstract

Context. Supersonic disordered flows accompany the formation and evolution of MCs. It has been argued that turbulence can support against gravitational collapse and form hierarchical sub-structures. Aims. We study the time evolution of simulated MCs to investigate: What physical process dominates the driving of turbulent flows? How can these flows be characterised? Do the simulated flows agree with observations? Methods. We analyse three MCs that have formed self-consistently within kpc-scale numerical simulations of the ISM. The simulated ISM evolves under the influence of physical processes including self-gravity, stratification, magnetic fields, supernova-driven turbulence, and radiative heating and cooling. We characterise the flows using VSFs with/out density weighting or a density cutoff, and computed in one or three dimensions. Results. In regions with sufficient resolution, the density-weighted VSFs initially appear to follow the expectations for uniform turbulence consistent with Larson's size-velocity relationship. SN blast wave impacts produce short-lived coherent motions at large scales, increasing the scaling exponents for a crossing time. Gravitational contraction drives small-scale motions, producing scaling coefficients that drop or even turn negative as small scales become dominant. Conclusions. We conclude that two different effects coincidentally reproduce Larson's size velocity relationship. Initially, uniform turbulence dominates, so the energy cascade produces VSFs consistent with Larson's relationship. Later, contraction dominates, the density-weighted VSFs become much shallower or even inverted, but the relationship of the global average velocity dispersion of the MCs to their radius follows Larson's relationship, reflecting virial equilibrium or free-fall collapse. The injection of energy by shocks is visible in the VSFs, but decays within a crossing time.

arXiv comment21 pages, 12 figures, accepted for publication in A&A

References in corpus (32)

• Control of star formation by supersonic turbulence
• Re-examining Larson's Scaling Relationships in Galactic Molecular Clouds
• The Universality of Turbulence in Galactic Molecular Clouds
• A new Jeans resolution criterion for (M)HD simulations of self-gravitating gas: Application to magnetic field amplification by gravity-driven turbulence
• Gravity or Turbulence? The velocity dispersion-size relation
• Molecular cloud evolution. I. Molecular cloud and thin CNM sheet formation
• On the Rapid Collapse and Evolution of Molecular Clouds
• Exact relation for correlation functions in compressible isothermal turbulence
• Supernova Driving. I. The Origin of Molecular Cloud Turbulence
• Gravity or turbulence? II. Evolving column density PDFs in molecular clouds
• Magnetic Fields in Population III Star Formation
• Turbulent Driving Scales in Molecular Clouds
• Exact Relation with Two-point Correlation Functions and Phenomenological Approach for Compressible Magnetohydrodynamic Turbulence
• Kolmogorov-Burgers Model for Star Forming Turbulence
• SILCC-Zoom: The dynamical and chemical evolution of molecular clouds
• Is the Scaling of Supersonic Turbulence Universal?
• The Power Spectrum of Supersonic Turbulence in Perseus
• Steady Outflows in Giant Clumps of High-z Disk Galaxies During Migration and Growth by Accretion
• The Turbulence Spectrum of Molecular Clouds in the Galactic Ring Survey: A Density-Dependent PCA Calibration
• Intermittency of interstellar turbulence: extreme velocity-shears and CO emission on milliparsec scale
• A supersonic turbulence origin of Larson's laws
• Gravitational contraction versus Supernova driving and the origin of the velocity dispersion-size relation in molecular clouds
• Structure Function Scaling in the Taurus and Perseus Molecular Cloud Complexes
• Rapid Star Formation and Global Gravitational Collapse
• Energy cascade and scaling in supersonic isothermal turbulence
• Observational Diagnostics of Self-Gravitating MHD Turbulence in Giant Molecular Clouds
• Feeding vs. Falling: The growth and collapse of molecular clouds in a turbulent interstellar medium
• Energy transfer in compressible magnetohydrodynamic turbulence for isothermal self-gravitating fluids
• Principal Component Analysis of Spectral Line Data: Analytic Formulation
• On the fragmentation of filaments in a molecular cloud simulation
• Influence of Shear Motion on Evolution of Molecular Clouds in the Spiral Galaxy M51
• Exact relations for energy transfer in self-gravitating isothermal turbulence

Cited by in corpus (15)

• Survival and mass growth of cold gas in a turbulent, multiphase medium
• Dynamical cloud formation traced by atomic and molecular gas
• Gravity Versus Magnetic Fields in Forming Molecular Clouds
• The Velocity Statistics of Turbulent Clouds in the Presence of Gravity, Magnetic fields, Radiation, and Outflow Feedback
• Empirical constraints on the turbulence in QSO host nebulae from velocity structure function measurements
• The "Maggie" filament: Physical properties of a giant atomic cloud
• Filamentary Hierarchies and Superbubbles I: Characterizing filament properties across a simulated spiral galaxy
• Shear, writhe and filaments: turbulence in the high latitude molecular cloud MBM 40
• Widespread subsonic turbulence in Ophiuchus North 1
• Star Cluster Formation in Clouds with Externally Driven Turbulence
• Ionized filaments and ongoing physical processes in massive star-forming sites around l = 345.5 degree
• Examining Turbulence in Galactic Molecular Clouds -- I: A Statistical Analysis of Velocity Structures
• On volume density and star formation in nearby molecular clouds
• Simulating High-Velocity Clouds in the Observational Plane: An Initial Study with the Smith Cloud
• Network of Star Formation: Fragmentation controlled by scale-dependent turbulent pressure and accretion onto the massive cores revealed in the Cygnus-X GMC complex