Influence of Cooling-Induced Compressibility on the Structure of Turbulent Flows and Gravitational Collapse

Abstract

We investigate the properties of highly compressible turbulence, the compressibility arising from a small effective polytropic exponent ${\gamma }_e$ due to cooling. In the limit of small ${\gamma }_e$, the density jump at shocks is shown to be of the order of $e^{M^2}$. Without self-gravity, the density structures arising in the moderately compressible case consist mostly of patches separated by shocks and behaving like waves, while in the highly compressible case clearly defined long-lived object-like clouds emerge. When the forcing in the momentum equation is purely compressible, the rotational energy decays monotonically in time, indicating that the vortex-stretching term is not efficient in transferring energy to rotational modes. This property may be at the origin of the low amount of rotation found in interstellar clouds. Vorticity production is found to rely heavily on the presence of additional terms in the equations. In the presence of self-gravity, we suggest that turbulence can produce bound structures for ${\gamma }_e<2(1-1/n)$, where $n$ is the typical dimensionality of the turbulent compressions. We support this result by means of numerical simulations in which, for sufficiently small ${\gamma }_e$, small-scale turbulent density fluctuations eventually collapse even though the medium is globally stable. This result is preserved in the presence of a magnetic field for supercritical mass-to-flux ratios. At larger polytropic exponents, turbulence alone is not capable of producing bound structures, and collapse can only occur when the medium is globally unstable. This mechanism is a plausible candidate for the differentiation between primordial and present-day stellar-cluster formation and for the low efficiency of star formation.

20 pages, 12 Postscript figures. Uses aas2pp4.sty. Accepted in ApJ

References in corpus (1)

• A Turbulent Model for the Interstellar Medium. II. Magnetic Fields and Rotation

Cited by in corpus (80)

• Control of star formation by supersonic turbulence
• Interstellar Turbulence I: Observations and Processes
• Gravitational Collapse in Turbulent Molecular Clouds. I. Gasdynamical Turbulence
• A Super-Alfvenic Model of Dark Clouds
• Massive Stars: Their Environment and Formation
• Molecular Cloud Evolution II. From cloud formation to the early stages of star formation in decaying conditions
• Global Hierarchical Collapse In Molecular Clouds. Towards a Comprehensive Scenario
• Density probability distribution in one-dimensional polytropic gas dynamics
• Turbulent molecular clouds
• Thermal condensation in a turbulent atomic hydrogen flow
• Turbulent Flow-Driven Molecular Cloud Formation: A Solution to the Post-T Tauri Problem?
• Turbulent Structure of a Stratified Supernova-Driven Interstellar Medium
• The Turbulent Shock Origin of Proto--Stellar Cores
• Molecular cloud evolution. I. Molecular cloud and thin CNM sheet formation
• Clouds as Turbulent Density Fluctuations. Implications for pressure confinement and spectral line data interpretation
• The Distribution of Thermal Pressures in the Interstellar Medium from a Survey of C I Fine-Structure Excitation
• Gravitational Collapse in Turbulent Molecular Clouds. II. Magnetohydrodynamical Turbulence
• On the Density Probability Function of Galactic Gas. I. Numerical Simulations and the Significance of the Polytropic Index
• Kinetic and Structural Evolution of Self-gravitating, Magnetized Clouds: 2.5-Dimensional Simulations of Decaying Turbulence
• Analytical theory for the initial mass function: II. Properties of the flow
• A Holistic Scenario of Turbulent Molecular Cloud Evolution and Control of the Star Formation Efficiency. First Tests
• The Lifetimes and Evolution of Molecular Cloud Cores
• Gravity-driven Turbulence in Galactic Disks
• The Formation of Self-Gravitating Cores in Turbulent Magnetized Clouds
• Kolmogorov-Burgers Model for Star Forming Turbulence
• High- and Low-Mass Star Forming Regions from Hierarchical Gravitational Fragmentation. High local Star Formation Rates with Low Global Efficiencies
• Scaling relations of supersonic turbulence in star-forming molecular clouds
• Six Myths on the Virial Theorem for Interstellar Clouds
• On the Existence of the Kolmogorov Inertial Range in the Terrestrial Magnetosheath Turbulence
• The Probability Distribution Function of Column Density in Molecular Clouds
• The Distribution of Pressures in a Supernova-Driven Interstellar Medium. I. Magnetized Medium
• Dynamic cores in hydrostatic disguise
• Is Thermal Instability Significant in Turbulent Galactic Gas?
• Formation of Cavities, Filaments, and Clumps by the Non-linear Development of Thermal and Gravitational Instabilities in the Interstellar Medium under Stellar Feedback
• The Polytropic Equation of State of Interstellar Gas Clouds
• Compressible magnetohydrodynamic turbulence in the Earth's magnetosheath: estimation of the energy cascade rate using in situ spacecraft data
• The ISM in spiral galaxies: can cooling in spiral shocks produce molecular clouds?
• The Formation of Molecular Clouds
• Fragmentation of massive dense cores down to ~1000 AU: Relation between fragmentation and density structure
• The nonlinear development of the thermal instability in the atomic ISM and its interaction with random fluctuations
• The Global Structure and Evolution of a Self-Gravitating Multi-phase Interstellar Medium in a Galactic Disk
• Turbulence in the Interstellar Medium
• The formation of the W43 complex: constraining its atomic-to-molecular transition and searching for colliding clouds
• Formation and loss of hierarchical structure in two-dimensional MHD simulations of wave-driven turbulence in interstellar clouds
• Does the magnetic field suppress fragmentation in massive dense cores?
• Emissivity Statistics in Turbulent, Compressible MHD Flows and the Density-Velocity Correlation
• The Stellar Mass Spectrum in Warm and Dusty Gas: Deviations from Salpeter in the Galactic Centre and in Circum-Nuclear Starburst Regions
• The pressure distribution in thermally bistable turbulent flows
• Turbulence from localized random expansion waves
• Does Turbulent Pressure Behave as a Logatrope?
• A Kolmogorov-Like Exact Relation for Compressible Polytropic Turbulence
• Turbulent dissipation in the ISM: the coexistence of forced and decaying regimes and implications for galaxy formation and evolution
• Formation and Collapse of Quiescent Cloud Cores Induced by Dynamic Compressions
• Supernova Driving. II. Compressive Ratio in Molecular-Cloud Turbulence
• Star cluster formation with stellar feedback and large-scale inflow
• The scaling relations and star formation laws of ministarburst complexes
• Hydrodynamical simulations of the decay of high-speed molecular turbulence. I. Dense molecular regions
• A Prescription for Star Formation Feedback: The Importance of Multiple Shell Interactions
• Interstellar MHD Turbulence and Star Formation
• Non-adiabatic turbulence driving during gravitational collapse
• Hydrodynamical simulations of the decay of high-speed molecular turbulence. II. Divergence from isothermality
• The Polytropic Equation of State of Primordial Gas Clouds
• Exact relations for energy transfer in self-gravitating isothermal turbulence
• Clustering Properties of Stars in Simulations of Wind-Driven Star Formation
• Relativistic Turbulence with Strong Synchrotron and Synchrotron-Self-Compton Cooling
• Wind-Driven Gas Networks and Star Formation in Galaxies: Reaction-Advection Hydrodynamic Simulations
• Velocity Structure of the ISM as Seen by the Spectral Correlation Function
• Large-scale turbulent driving regulates star formation in high-redshift gas-rich galaxies II: Influence of the magnetic field and the turbulent compressive fraction
• Evolution of the angular momentum during gravitational fragmentation of molecular clouds
• Variation of the Core Lifetime and Fragmentation Scale in Molecular Clouds as an Indication of Ambipolar Diffusion
• A Dynamically Collapsing Core and a Precursor of a Core in a Filament Supported by Turbulent and Magnetic Pressures
• Turbulent Compressibilty of Protogalactic Gas
• Testing assumptions and predictions of star-formation theories
• Molecular Clouds. Formation and Disruption
• Shocks in the warm neutral medium I -- Theoretical model
• The role of shocks and the velocity gradient in the relative orientation of the magnetic field and dense gas clouds
• Shocks in the warm neutral medium II -- Origin of neutral carbon at high pressure
• Turbulent Control of the Star Formation Efficiency
• Formation of prestellar cores via non-isothermal gas fragmentation
• Energy Budget and the Virial Theorem in Interstellar Clouds