Probing the evolution of molecular cloud structure II: From chaos to confinement

Abstract

We present an analysis of the large-scale molecular cloud structure and of the stability of clumpy structures in nearby molecular clouds. In our recent work, we identified a structural transition in molecular clouds by studying the probability distributions of gas column densities in them. In this paper, we further examine the nature of this transition. The transition takes place at the visual extinction of A_V^tail = 2-4 mag, or equivalently, at Σ^tail = 40-80 Ms pc^{-2}. The clumps identified above this limit have wide ranges of masses and sizes, but a remarkably constant mean volume density of n = 10^3 cm^{-3}. This is 5-10 times larger than the density of the medium surrounding the clumps. By examining the stability of the clumps, we show that they are gravitationally unbound entities, and that the external pressure from the parental molecular cloud is a significant source of confining pressure for them. Then, the structural transition at A_V^tail may be linked to a transition between this population and the surrounding medium. The star formation rates in the clouds correlate strongly with the total mass in the clumps, i.e, with the mass above A_V^tail, dropping abruptly below that threshold. These results imply that the formation of pressure confined clumps introduces a prerequisite for star formation. Furthermore, they give a physically motivated explanation for the recently reported relation between the star formation rates and the amount of dense material in molecular clouds. Likewise, they give rise to a natural threshold for star formation at A_V^tail.

11 pages, 12 figures, accepted for publication in Astronomy and Astrophysics

References in corpus (20)

• Theory of Star Formation
• On the Star Formation Rates in Molecular Clouds
• The Density Probability Distribution in Compressible Isothermal Turbulence: Solenoidal versus Compressive Forcing
• The Star Formation Rate and Gas Surface Density Relation in the Milky Way: Implications for Extragalactic Studies
• The COMPLETE Survey of Star-Forming Regions: Phase I Data
• The relation between gas and dust in the Taurus Molecular Cloud
• On the Density Distribution in Star-forming Interstellar Clouds
• The Nature of the Dense Core Population in the Pipe Nebula: Thermal Cores Under Pressure
• 2MASS wide field extinction maps - I. The Pipe nebula
• The Fractal Density Structure in Supersonic Isothermal Turbulence: Solenoidal versus Compressive Energy Injection
• Hipparcos distances of Ophiuchus and Lupus cloud complexes
• Variations in Stellar Clustering with Environment: Dispersed Star Formation and the Origin of Faint Fuzzies
• NICEST, a near-infrared color excess method tailored for small-scale structures
• The Perils of Clumpfind: The Mass Spectrum of Sub-structures in Molecular Clouds
• Six Myths on the Virial Theorem for Interstellar Clouds
• 2MASS wide field extinction maps: II. The Ophiuchus and the Lupus cloud complexe
• Turbulent Mixing in the Interstellar Medium -- an application for Lagrangian Tracer Particles
• The COMPLETE Nature of the Warm Dust Ring in Perseus
• Enhanced Core Formation Rate in a Turbulent Cloud by Self-gravity
• On the fidelity of the core mass functions derived from dust column density data

Cited by in corpus (80)

• Star Formation in the Milky Way and Nearby Galaxies
• On the Star Formation Efficiency of Turbulent Magnetized Clouds
• What determines the density structure of molecular clouds ? A case study of Orion B with Herschel
• Dispersal of molecular clouds by ionising radiation
• The ATLASGAL survey: a catalog of dust condensations in the Galactic plane
• Gravity or turbulence? II. Evolving column density PDFs in molecular clouds
• Vertical structure of a supernova-driven turbulent magnetized ISM
• High-dynamic-range extinction mapping of infrared dark clouds: Dependence of density variance with sonic Mach number in molecular clouds
• Molecular Line Emission as a Tool for Galaxy Observations (LEGO). I. HCN as a tracer of moderate gas densities in molecular clouds and galaxies
• Understanding star formation in molecular clouds I. Effects of line-of-sight contamination on the column density structure
• Is molecular gas necessary for star formation?
• Class 0 Protostars in the Perseus Molecular Cloud: A Correlation Between the Youngest Protostars and the Dense Gas Distribution
• The first Hi-GAL observations of the outer Galaxy: a look to star formation in the third Galactic quadrant in the longitude range 216.5 < l < 225.5
• Analytical theory for the initial mass function: III time dependence and star formation rate
• The Galactic Center Cloud G0.253+0.016: A Massive Dense Cloud with low Star Formation Potential
• Gravitational Infall onto Molecular Filaments
• The Hi-GAL compact source catalogue -- II. The 360° catalogue of clump physical properties
• Detection of two power-law tails in the probability distribution functions of massive GMCs
• The Panchromatic Hubble Andromeda Treasury VIII: A Wide-Area, High-Resolution Map of Dust Extinction in M31
• The Column Density Variance-Sonic Mach Number Relationship
• Understanding star formation in molecular clouds II. Signatures of gravitational collapse of IRDCs
• Gravitational fragmentation caught in the act: the filamentary Musca molecular cloud
• Herschel's view of the large-scale structure in the Chamaeleon dark clouds
• The shapes of column density PDFs - The importance of the last closed contour
• Observational Diagnostics of Self-Gravitating MHD Turbulence in Giant Molecular Clouds
• Filament Fragmentation in High-Mass Star Formation
• From diffuse gas to dense molecular cloud cores
• Herschel far-infrared observations of the Carina Nebula complex I: Introduction and global cloud structure
• Connection between dense gas mass fraction, turbulence driving, and star formation efficiency of molecular clouds
• The dynamics and star-forming potential of the massive Galactic centre cloud G0.253+0.016
• Zooming in on Individual Star Formation: Low- and High-mass Stars
• Hierarchical Structure of Magnetohydrodynamic Turbulence In Position-Position-Velocity Space
• Understanding star formation in molecular clouds IV. Column density PDFs from quiescent to massive molecular clouds
• On the Appearance of Thresholds in the Dynamical Model of Star Formation
• An Ammonia Spectral Map of the L1495-B218 Filaments in the Taurus Molecular Cloud : I. Physical Properties of Filaments and Dense cores
• The Dependence of Star Formation Efficiency on Gas Surface Density
• SIRIUS project. I. Star formation models for star-by-star simulations of star clusters and galaxy formation
• The Darkest Shadows: Deep Mid-Infrared Extinction Mapping of a Massive Protocluster
• Evolving Molecular Cloud Structure and the Column Density Probability Distribution Function
• The reliability of observational measurements of column density probability distribution functions
• 13CO Cores in Taurus Molecular Cloud
• The Multi-phase Turbulence Density Power Spectra in the Perseus Molecular Cloud
• IRAM-30m large scale survey of ${}^{12}$CO(2-1) and ${}^{13}$CO(2-1) emission in the Orion molecular cloud
• 3D Extinction Mapping Using Hierarchical Bayesian Models
• The HI Probability Distribution Function and the Atomic-to-Molecular Transition in Molecular Clouds
• A molecular line study of the filamentary infrared dark cloud G304.74+01.32
• The Density Distribution in Turbulent Bi-stable Flows
• A Simple Perspective on the Mass-Area Relationship in Molecular Clouds
• Analytical core mass function (CMF) from filaments: Under which circumstances can filament fragmentation reproduce the CMF?
• The census of dense cores in the Serpens region from the Herschel Gould Belt Survey
• Power-law tails in probability density functions of molecular cloud column density
• APEX/SABOCA observations of small-scale structure of infrared-dark clouds I. Early evolutionary stages of star-forming cores
• The relation between the turbulent Mach number and observed fractal dimensions of turbulent clouds
• The Coalsack near and far
• The evolution of temperature and density structures of OB cluster-forming molecular clumps
• Relationship between the column density distribution and evolutionary class of molecular clouds as viewed by ATLASGAL
• A possible observational bias in the estimation of the virial parameter in virialized clumps
• What is the physics behind the Larson mass-size relation?
• Fragmentation and kinematics in high-mass star formation: CORE-extension targeting two very young high-mass star-forming regions
• Effect of feedback of massive stars in the fragmentation, distribution, and kinematics of the gas in two star forming regions in the Carina Nebula
• Galactic cold cores IX. Column density structures and radiative transfer modelling
• The relation between the true and observed fractal dimensions of turbulent clouds
• Squeezed between shells? On the origin of the Lupus I molecular cloud. APEX/LABOCA, Herschel, and Planck observations
• A network of filaments detected by Herschel in the Serpens Core: A laboratory to test simulations of low-mass star formation
• Constructing multi-scale gravitational energy spectra from molecular cloud surface density PDF -- Interplay between turbulence and gravity
• The Probability Distribution Function of Gas Surface Density in M33
• High-mass star formation at high luminosities: W31 at >10^6 L_sun
• Sheets, filaments and clumps - high resolution simulations of how the thermal instability can form molecular clouds
• The "Maggie" filament: Physical properties of a giant atomic cloud
• Opacity Broadening of ${}^{13}$CO Linewidths and its Effect on the Variance-Sonic Mach Number Relation
• The Clump Mass Function of the Dense Clouds in the Carina Nebula Complex
• Clump mass function at an early stage of molecular cloud evolution: I. A statistical approach
• Rethinking a Mysterious Molecular Cloud
• Properties of the dense cores and filamentary structures in the Vela C molecular cloud
• The Dependence of Prestellar Core Mass Distributions on the Structure of the Parental Cloud
• Revisiting The Mass-Size Relation Of Structures In Molecular Clouds
• A new parameterization of the star formation rate-dense gas mass relation: embracing gas density gradients
• Measuring the spectral index of turbulent gas with deep learning from projected density maps
• Cold atomic gas identified by HI self-absorption. Cold atomic clouds toward giant molecular filaments
• Contour Analysis Tool: an interactive tool for background and morphology analysis