Centroid Velocity Statistics of Molecular Clouds

Abstract

We compute structure functions and Fourier spectra of 2D centroid velocity (CV) maps in order to study the gas dynamics of typical molecular clouds (MCs) in numerical simulations. We account for a simplified treatment of time-dependent chemistry and the non-isothermal nature of the gas and use a 3D radiative transfer tool to model the CO line emission in a post-processing step. We perform simulations using three different initial mean number densities of n_0 = 30, 100 and 300 cm^{-3} to span a range of typical values for dense gas clouds in the solar neighbourhood. We compute slopes of the centroid velocity increment structure functions (CVISF) and of Fourier spectra for different chemical components: the total density, H2 number density, 12CO number density as well as the integrated intensity of 12CO (J=1-0) and 13CO (J=1-0). We show that optical depth effects can significantly affect the slopes derived for the CVISF, which also leads to different scaling properties for the Fourier spectra. The slopes of CVISF and Fourier spectra for H2 are significantly steeper than those for the different CO tracers, independent of the density and the numerical resolution. This is due to the larger space-filling factor of H2 as it is better able to self-shield in diffuse regions, leading to a larger fractal co-dimension compared to CO.

arXiv comment12 pages, 6 figures, submitted to MNRAS

References in corpus (46)

• Theory of Star Formation
• Control of star formation by supersonic turbulence
• Interstellar Turbulence I: Observations and Processes
• Comparing the statistics of interstellar turbulence in simulations and observations: Solenoidal versus compressive turbulence forcing
• The Statistics of Supersonic Isothermal Turbulence
• The photodissociation and chemistry of CO isotopologues: applications to interstellar clouds and circumstellar disks
• The Energy Dissipation Rate of Supersonic, Magnetohydrodynamic Turbulence in Molecular Clouds
• The Density Probability Distribution in Compressible Isothermal Turbulence: Solenoidal versus Compressive Forcing
• Kinetic Energy Decay Rates of Supersonic and Super-Alfvenic Turbulence in Star-Forming Clouds
• Velocity Modification of HI Power Spectrum
• Physical Properties and Galactic Distribution of Molecular Clouds identified in the Galactic Ring Survey
• Turbulent molecular clouds
• Interstellar Turbulence II: Implications and Effects
• Simulating Radiating and Magnetized Flows in Multi-Dimensions with ZEUS-MP
• Simulating the formation of molecular clouds. I. Slow formation by gravitational collapse from static initial conditions
• Density Fluctuations in MHD Turbulence: Spectra, Intermittency and Topology
• On the Relationship Between Molecular Hydrogen and Carbon Monoxide Abundances in Molecular Clouds
• Modeling CO Emission: I. CO as a Column Density Tracer and the X-Factor in Molecular Clouds
• Velocity and density spectra of the Small Magellanic Cloud
• Velocity Modification of Power Spectrum from Absorbing Medium
• Characterizing Magnetohydrodynamic Turbulence in the Small Magellanic Cloud
• Bottleneck effect in three-dimensional turbulence simulations
• The Probability Distribution Function of Column Density in Molecular Clouds
• Studying Turbulence using Doppler-broadened lines: Velocity Coordinate Spectrum
• A new density variance - Mach number relation for subsonic and supersonic, isothermal turbulence
• The Power Spectrum of Supersonic Turbulence in Perseus
• New Regime of MHD Turbulence: Cascade Below Viscous Cutoff
• Supersonic turbulence and structure of interstellar molecular clouds
• The Column Density Variance-Sonic Mach Number Relationship
• The Spectral Correlation Function -- A New Tool for Analyzing Spectral-Line Maps
• Comparison of spectral slopes of magnetohydrodynamic and hydrodynamic turbulence and measurements of alignment effects
• Density Probability Distribution Functions in Supersonic Hydrodynamic and MHD Turbulence
• Inertial range scaling in numerical turbulence with hyperviscosity
• Carbon Fractionation in PDRs
• The ${}^{12}$CO/${}^{13}$CO ratio in turbulent molecular clouds
• Structure analysis of interstellar clouds: I. Improving the Delta-variance method
• Statistics of Velocity from Spectral Data: Modified Velocity Centroids
• Statistical properties of supersonic turbulence in the Lagrangian and Eulerian frameworks
• The Turbulence Power Spectrum in Optically Thick Interstellar Clouds
• Measuring the Alfvenic Nature of the Interstellar Medium: Velocity Anisotropy Revisited
• Dissipative structures of diffuse molecular gas III -- Small-scale intermittency of intense velocity-shears
• Interstellar cloud structure: The statistics of centroid velocities
• Structure analysis of interstellar clouds: II. Applying the Delta-variance method to interstellar turbulence
• The Effects of Radiative Transfer on the PDFs of Molecular MHD Turbulence
• Principal Component Analysis of Molecular Clouds: Can CO reveal the dynamics?
• Introducing ZEUS-MP: A 3D, Parallel, Multiphysics Code for Astrophysical Fluid Dynamics

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• Mach number study of supersonic turbulence: The properties of the density field
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• Statistical model for filamentary structures of molecular clouds -- The modified multiplicative random cascade model and its multifractal nature
• Spatial Power Spectra of Dust across the Local Group: No Constraint on Disc Scale Height
• A new method for spatially resolving the turbulence driving mixture in the ISM with application to the Small Magellanic Cloud
• An Exploration of the Statistical Signatures of Stellar Feedback
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• Exposing the plural nature of molecular clouds : Extracting filaments and the CIB against the true scale-free interstellar medium
• Diagnosing Turbulence in the Neutral and Molecular Interstellar Medium of Galaxies