Probes of turbulent driving mechanisms in molecular clouds from fluctuations in synchrotron intensity

Abstract

Previous studies have shown that star formation depends on the driving of molecular cloud turbulence, and differences in the driving can produce an order of magnitude difference in the star formation rate. The turbulent driving is characterised by the parameter $\zeta$, with $\zeta =0$ for compressive, curl-free driving (e.g. accretion or supernova explosions), and $\zeta =1$ for solenoidal, divergence-free driving (e.g. Galactic shear). Here we develop a new method to measure $\zeta$ from observations of synchrotron emission from molecular clouds. We calculate statistics of mock synchrotron intensity images produced from magnetohydrodynamic simulations of molecular clouds, in which the driving was controlled to produce different values of $\zeta$. We find that the mean and standard deviation of the log-normalised synchrotron intensity are sensitive to $\zeta$, for values of $\zeta$ between $0$ (curl-free driving) and $0.5$ (naturally-mixed driving). We quantify the dependence of zeta on the direction of the magnetic field relative to the line of sight. We provide best-fit formulae for $\zeta$ in terms of the log-normalised mean and standard deviation of synchrotron intensity, with which $\zeta$ can be determined for molecular clouds that have similar Alfvénic Mach number to our simulations. These formulae are independent of the sonic Mach number. Signal-to-noise ratios larger than $5$, and angular resolutions smaller than $5\%$ of the cloud diameter, are required to apply these formulae. Although there are no firm detections of synchrotron emission from molecular clouds, by combining Green Bank Telescope and Very Large Array observations it should be possible to detect synchrotron emission from molecular clouds, thereby constraining the value of $\zeta$.

arXiv comment14 pages, 6 figures, accepted by MNRAS

References in corpus (58)

• Theory of Star Formation
• Control of star formation by supersonic turbulence
• Interstellar Turbulence I: Observations and Processes
• The Interstellar Environment of our Galaxy
• Comparing the statistics of interstellar turbulence in simulations and observations: Solenoidal versus compressive turbulence forcing
• The Star Formation Rate of Turbulent Magnetized Clouds: Comparing Theory, Simulations, and Observations
• The Statistics of Supersonic Isothermal Turbulence
• Compressible Magnetohydrodynamic Turbulence: mode coupling, scaling relations, anisotropy, new regime and astrophysical implications
• The Density Probability Distribution in Compressible Isothermal Turbulence: Solenoidal versus Compressive Forcing
• The Universality of Turbulence in Galactic Molecular Clouds
• Radio observational constraints on Galactic 3D-emission models
• What is Driving the HI Velocity Dispersion?
• Accretion-Driven Turbulence as Universal Process: Galaxies, Molecular Clouds, and Protostellar Disks
• A new Jeans resolution criterion for (M)HD simulations of self-gravitating gas: Application to magnetic field amplification by gravity-driven turbulence
• On the universality of supersonic turbulence
• Broad-band nonthermal emission from molecular clouds illuminated by cosmic rays from nearby supernova remnants
• What determines the density structure of molecular clouds ? A case study of Orion B with Herschel
• Density Fluctuations in MHD Turbulence: Spectra, Intermittency and Topology
• Inefficient star formation through turbulence, magnetic fields and feedback
• Mach Number Dependence of Turbulent Magnetic Field Amplification: Solenoidal versus Compressive Flows
• Numerical simulations of compressively driven interstellar turbulence: I. Isothermal gas
• The Fractal Density Structure in Supersonic Isothermal Turbulence: Solenoidal versus Compressive Energy Injection
• The link between turbulence, magnetic fields, filaments, and star formation in the Central Molecular Zone cloud G0.253+0.016
• Density Studies of MHD Interstellar Turbulence: Statistical Moments, Correlations and Bispectrum
• Supernova Driving. I. The Origin of Molecular Cloud Turbulence
• The generation of strong magnetic fields during the formation of the first stars
• Velocity Field of Compressible MHD Turbulence: Wavelet Decomposition and Mode Scalings
• A robust numerical scheme for highly compressible magnetohydrodynamics: Nonlinear stability, implementation and tests
• Starbursts triggered by inter-galactic tides and interstellar compressive turbulence
• Is Turbulence in the Interstellar Medium Driven by Feedback or Gravity? An Observational Test
• Low-Mach-number turbulence in interstellar gas revealed by radio polarization gradients
• The density variance -- Mach number relation in supersonic, isothermal turbulence
• Turbulent Driving Scales in Molecular Clouds
• Gamma rays from molecular clouds
• A Dynamical Model for the Formation of Gas Rings and Episodic Starbursts Near Galactic Centres
• Characterizing Magnetohydrodynamic Turbulence in the Small Magellanic Cloud
• On the Dynamics and Evolution of Gravitational Instability-Dominated Disks
• Simulations of magnetized multiphase galactic disk regulated by supernovae explosions
• Adiabatic Heating of Contracting Turbulent Fluids
• Spectral Properties of Compressible Magnetohydrodynamic Turbulence from Numerical Simulations
• A new density variance - Mach number relation for subsonic and supersonic, isothermal turbulence
• The Turbulence Spectrum of Molecular Clouds in the Galactic Ring Survey: A Density-Dependent PCA Calibration
• The Column Density Variance-Sonic Mach Number Relationship
• Turbulent Gas Flows in the Rosette and G216-2.5 Molecular Clouds: Assessing Turbulent Fragmentation Descriptions of Star Formation
• Connection between dense gas mass fraction, turbulence driving, and star formation efficiency of molecular clouds
• Statistical properties of supersonic turbulence in the Lagrangian and Eulerian frameworks
• Modeling H2 formation in the turbulent ISM: Solenoidal versus compressive turbulent forcing
• Milky Way Star Forming Complexes and the Turbulent Motion of the Galaxy's Molecular Gas
• A measurement of the turbulence-driven density distribution in a non-star-forming molecular cloud
• Vorticity production through rotation, shear and baroclinicity
• Radio Synchrotron Fluctuation Statistics as a Probe of Magnetized Interstellar Turbulence
• An Observational Method to Measure the Relative Fractions of Solenoidal and Compressible Modes in Interstellar Clouds
• The onset of large scale turbulence in the interstellar medium of spiral galaxies
• 74 MHz Nonthermal Emission from Molecular Clouds: Evidence for a Cosmic Ray Dominated Region at the Galactic Center
• Interpretation of radio continuum and molecular line observations of Sgr B2: free-free and synchrotron emission, and implications for cosmic rays
• Cosmic Ray Sampling of a Clumpy Interstellar Medium
• Australia Telescope Compact Array Radio Continuum 1384 and 2368 Mhz Observations of Sagittarius B
• Constraints on free-free emission from Anomalous Microwave Emission Sources in the Perseus Molecular Cloud

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• The Self-gravitating Gas Fraction and The Critical Density for Star Formation
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• The Anatomy of the Column Density Probability Distribution Function (N-PDF)
• On the dynamics and survival of fractal clouds in galactic winds
• Practical Modeling of Large-Scale Galactic Magnetic Fields: Status and Prospects
• The driving of turbulence in simulations of molecular cloud formation and evolution
• Studies of Turbulence Dissipation in Taurus Molecular Cloud with Core Velocity Dispersion (CVD)
• The driving scale -- density decorrelation scale relation in a turbulent medium
• Tracing magnetic fields by the synergies of synchrotron emission gradients
• Tracing Magnetic Field with Synchrotron Polarization Gradients: Parameter Study
• Observed Faraday Effects in Damped Lyman-Alpha Absorbers and Lyman Limit Systems: The Magnetised Environment of Galactic Building Blocks at Redshift=2
• Advanced Diagnostics for the Study of Linearly Polarized Emission. II: Application to Diffuse Interstellar Radio Synchrotron Emission
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