Understanding star formation in molecular clouds I. Effects of line-of-sight contamination on the column density structure

Abstract

Column-density maps of molecular clouds are one of the most important observables in the context of molecular cloud- and star-formation (SF) studies. With the Herschel satellite it is now possible to determine the column density from dust emission. We use observations and simulations to demonstrate how LOS contamination affects the column density probability distribution function (PDF). We apply a first-order approximation (removing a constant level) to the molecular clouds of Auriga, Maddalena, Carina and NGC3603. In perfect agreement with the simulations, we find that the PDFs become broader, the peak shifts to lower column densities, and the power-law tail of the PDF flattens after correction. All PDFs have a lognormal part for low column densities with a peak at Av~2, a deviation point (DP) from the lognormal at Av(DP)~4-5, and a power-law tail for higher column densities. Assuming a density distribution rho~r^-alpha, the slopes of the power-law tails correspond to alpha(PDF)=1.8, 1.75, and 2.5 for Auriga, Carina, and NGC3603 (alpha~1.5-2 is consistent gravitational collapse). We find that low-mass and high-mass SF clouds display differences in the overall column density structure. Massive clouds assemble more gas in smaller cloud volumes than low-mass SF ones. However, for both cloud types, the transition of the PDF from lognormal shape into power-law tail is found at the same column density (at Av~4-5 mag). Low-mass and high-mass SF clouds then have the same low column density distribution, most likely dominated by supersonic turbulence. At higher column densities, collapse and external pressure can form the power-law tail. The relative importance of the two processes can vary between clouds and thus lead to the observed differences in PDF and column density structure.

arXiv commentA&A accepted, 15.12. 2014

References in corpus (62)

• Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy
• The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
• The Herschel-SPIRE instrument and its in-flight performance
• From filamentary clouds to prestellar cores to the stellar IMF: Initial highlights from the Herschel Gould Belt survey
• A General Theory of Turbulence-Regulated Star Formation, From Spirals to ULIRGs
• The Stellar IMF from Turbulent Fragmentation
• Comparing the statistics of interstellar turbulence in simulations and observations: Solenoidal versus compressive turbulence forcing
• Characterizing interstellar filaments with Herschel in IC5146
• The Star Formation Rate of Turbulent Magnetized Clouds: Comparing Theory, Simulations, and Observations
• On the Star Formation Rates in Molecular Clouds
• Re-examining Larson's Scaling Relationships in Galactic Molecular Clouds
• Herschel view of the Taurus B211/3 filament and striations: Evidence of filamentary growth?
• Analytical theory for the initial mass function: CO clumps and prestellar cores
• Large-Scale Structure of the Molecular Gas in Taurus Revealed by High Linear Dynamic Range Spectral Line Mapping
• Probing the evolution of molecular cloud structure: From quiescence to birth
• Cores, filaments, and bundles: hierarchical core formation in the L1495/B213 Taurus region
• On the Star Formation Efficiency of Turbulent Magnetized Clouds
• Density probability distribution in one-dimensional polytropic gas dynamics
• Dynamic star formation in the massive DR21 filament
• Cluster-formation in the Rosette molecular cloud at the junctions of filaments
• One-Point Probability Distribution Functions of Supersonic Turbulent Flows in Self-Gravitating Media
• Mapping the interstellar dust with near-infrared observations: An optimized multi-band technique
• What determines the density structure of molecular clouds ? A case study of Orion B with Herschel
• Scanamorphos: a map-making software for Herschel and similar scanning bolometer arrays
• On the Density Distribution in Star-forming Interstellar Clouds
• Filaments and ridges in Vela C revealed by Herschel: from low-mass to high-mass star-forming sites
• 2MASS wide field extinction maps - I. The Pipe nebula
• The spine of the swan: A Herschel study of the DR21 ridge and filaments in Cygnus X
• Supersonic turbulence in the ISM: stellar extinction determinations as probes of the structure and dynamics of dark clouds
• The "True" Column Density Distribution in Star-Forming Molecular Clouds
• Physical vs. Observational Properties of Clouds in Turbulent Molecular Cloud Models
• Gravity or turbulence? II. Evolving column density PDFs in molecular clouds
• Analytical theory for the initial mass function: II. Properties of the flow
• On the evolution of the density pdf in strongly self-gravitating systems
• Reconstructing the density and temperature structure of prestellar cores from $Herschel$ data: A case study for B68 and L1689B
• The California Molecular Cloud
• The link between molecular cloud structure and turbulence
• NICEST, a near-infrared color excess method tailored for small-scale structures
• The Probability Distribution Function of Column Density in Molecular Clouds
• Larson's third law and the universality of molecular cloud structure
• 2MASS wide field extinction maps: II. The Ophiuchus and the Lupus cloud complexe
• Two Mass Distributions in the L 1641 Molecular Clouds: The Herschel connection of Dense Cores and Filaments in Orion A
• The Structure of Molecular Clouds: I - All Sky Near Infrared Extinction Maps
• Ionization compression impact on dense gas distribution and star formation, Probability density functions around H ii regions as seen by Herschel
• Probing the evolution of molecular cloud structure II: From chaos to confinement
• Herschel's view of the large-scale structure in the Chamaeleon dark clouds
• The formation of the W43 complex: constraining its atomic-to-molecular transition and searching for colliding clouds
• 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
• A method for reconstructing the PDF of a 3D turbulent density field from 2D observations
• Large scale IRAM 30m CO-observations in the giant molecular cloud complex W43
• A First Look at the Auriga-California Giant Molecular Cloud With Herschel and the CSO: Census of the Young Stellar Objects and the Dense Gas
• Herschel far-infrared observations of the Carina Nebula Complex. - III: Detailed cloud structure and feedback effects
• Turbulent Mixing in the Interstellar Medium -- an application for Lagrangian Tracer Particles
• 2MASS wide field extinction maps: V. Corona Australis
• Herschel Observations of the W3 GMC: Clues to the Formation of Clusters of High-Mass Stars
• Variation of the extinction law in the Trifid nebula
• Evolving Molecular Cloud Structure and the Column Density Probability Distribution Function
• Herschel far-infrared observations of the Carina Nebula complex II: The embedded young stellar and protostellar population
• Enhanced Core Formation Rate in a Turbulent Cloud by Self-gravity
• Young stellar clusters in the Rosette molecular cloud. Arguments against triggered star formation
• The Effects of Radiative Transfer on the PDFs of Molecular MHD Turbulence

Cited by in corpus (91)

• Star Clusters Across Cosmic Time
• The link between turbulence, magnetic fields, filaments, and star formation in the Central Molecular Zone cloud G0.253+0.016
• Multi-temperature mapping of dust structures throughout the Galactic Plane using the PPMAP tool with Herschel Hi-GAL data
• A census of dense cores in the Taurus L1495 cloud from the Herschel Gould Belt Survey
• Molecular clouds have power-law probability distribution functions
• 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
• Numerical Simulations of Turbulent, Molecular Clouds Regulated by Radiation Feedback Forces I: Star Formation Rate and Efficiency
• Understanding star formation in molecular clouds II. Signatures of gravitational collapse of IRDCs
• High-mass Star Formation through Filamentary Collapse and Clump-fed Accretion in G22
• The ATLASGAL survey: distribution of cold dust in the Galactic plane. Combination with Planck data
• From parallel to perpendicular -- On the orientation of magnetic fields in molecular clouds
• Understanding star formation in molecular clouds III. Probability distribution functions of molecular lines in Cygnus X
• The shapes of column density PDFs - The importance of the last closed contour
• Observational Diagnostics of Self-Gravitating MHD Turbulence in Giant Molecular Clouds
• The rate and latency of star formation in dense, massive clumps in the Milky Way
• The Razor's Edge of Collapse: The Transition Point from Lognormal to Powerlaw in Molecular Cloud PDFs
• Filament formation in wind-cloud interactions. II. Clouds with turbulent density, velocity, and magnetic fields
• A $Herschel-SPIRE$ Survey of the Mon R2 Giant Molecular Cloud: Analysis of the Gas Column Density Probability Density Function
• Understanding star formation in molecular clouds IV. Column density PDFs from quiescent to massive molecular clouds
• Cloud Structure of Galactic OB Cluster Forming Regions from Combining Ground and Space Based Bolometric Observations
• On the Appearance of Thresholds in the Dynamical Model of Star Formation
• The dense cores and filamentary structure of the molecular cloud in Corona Australis. Herschel SPIRE and PACS observations from the Herschel Gould Belt Survey
• The Anatomy of the Column Density Probability Distribution Function (N-PDF)
• Physical properties of the ambient medium and of dense cores in the Perseus star-forming region derived from Herschel Gould Belt Survey observations
• FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope (FUGIN) 2: Possible evidence for formation of NGC~6618 cluster in M17 by cloud-cloud collision
• SIRIUS project. I. Star formation models for star-by-star simulations of star clusters and galaxy formation
• Photoevaporation of Jeans-unstable molecular clumps
• The reliability of observational measurements of column density probability distribution functions
• On the shape and completeness of the column density probability distribution function of molecular clouds
• Gaia Data Release 3 Validating the classification of variable Young Stellar Object candidates
• Filaments in the Lupus molecular clouds
• Synthetic observations of star formation and the interstellar medium
• The HI Probability Distribution Function and the Atomic-to-Molecular Transition in Molecular Clouds
• Establishing the evolutionary timescales of the massive star formation process through chemistry
• Dense molecular gas properties on 100 pc scales across the disc of NGC 3627
• Velocity Gradient in the Presence of Self-Gravity: Identifying Gravity-induced Inflow and Determining Collapsing Stage
• Numerical Simulations of Turbulent Molecular Clouds Regulated by Radiation Feedback Forces II: Radiation-Gas Interactions and Outflows
• The Distribution of Mass Surface Densities in a High-Mass Protocluster
• On the compressive nature of turbulence driven by ionising feedback in the pillars of the Carina Nebula
• The density structure of supersonic self-gravitating turbulence
• Effects of initial density profiles on massive star cluster formation in giant molecular clouds
• Filaments and striations: anisotropies in observed, supersonic, highly-magnetised turbulent clouds
• Power-law tails in probability density functions of molecular cloud column density
• The driving of turbulence in simulations of molecular cloud formation and evolution
• The Dust in M31
• Herschel observations of the Galactic HII region RCW 79
• Bird's eye view of molecular clouds in the Milky Way: I. Column density and star formation from sub-pc to kpc scales
• Molecular Clouds in the Second Quadrant of the Milky Way Mid-plane from l$=$104$.{}^{\circ }$75 to l=119$.{}^{\circ }$75 and b=$-$5$.{}^{\circ }$25 to b=5$.{}^{\circ }$25
• Cloud Properties and Correlations with Star Formation in Numerical Simulations of the Three-Phase ISM
• On the accuracy of HI observations in molecular clouds -- More cold HI than thought?
• Relationship between the column density distribution and evolutionary class of molecular clouds as viewed by ATLASGAL
• Dense Gas in a Giant Molecular Filament
• Small-scale physical and chemical structure of diffuse and translucent molecular clouds along the line of sight to Sgr B2
• Low Mass Stars as Tracers of Star and Cluster Formation
• Galactic cold cores IX. Column density structures and radiative transfer modelling
• The Parsec-Scale Relationship Between I_CO and A_V in Local Molecular Clouds
• Squeezed between shells? On the origin of the Lupus I molecular cloud. APEX/LABOCA, Herschel, and Planck observations
• Opening the Treasure Chest in Carina
• On the extraction of power-law parts of the probability density functions in star-forming clouds
• An Estimation of the Star Formation Rate in the Perseus Complex
• A network of filaments detected by Herschel in the Serpens Core: A laboratory to test simulations of low-mass star formation
• Statistical link between the structure of molecular clouds and their density distribution
• The Probability Distribution Function of Gas Surface Density in M33
• The "Maggie" filament: Physical properties of a giant atomic cloud
• Infrared dust bubble CS51 and its interaction with the surrounding interstellar medium
• Modelling the structure of molecular clouds: I. A multi-scale energy equipartition
• On the Diagnostic Power of FIR/Sub-mm SED Fitting in Massive Galactic Molecular Clumps
• Star Cluster Formation in Orion A
• Tracing the general structure of Galactic molecular clouds using Planck data: I. The Perseus region as a test case
• A Synergy of the Velocity Gradients Technique and the Probability Density Functions for Identifying Gravitational Collapse in Self-Absorbing Media
• Star formation in evolving molecular clouds
• 25 years of XMM-Newton observations of the Sgr A complex: 3D distribution and internal structure of the clouds
• Externally irradiated young stars in NGC 3603. A JWST NIRSpec catalogue of pre-main-sequence stars in a massive star formation region
• Reconciling extragalactic star formation efficiencies with theory: insights from PHANGS
• The Transition from a Lognormal to a Power-Law Column Density Distribution in Molecular Clouds: An Imprint of the Initial Magnetic Field and Turbulence
• Multi log-normal density structure in Cygnus-X molecular clouds: A fitting for N-PDF without power-law
• Statistical properties and correlation length in star-forming molecular clouds: I. Formalism and application to observations
• Extraction of a second power-law tail of the density distribution in simulated clouds
• The turbulence driving parameter of molecular clouds in disc galaxies
• A new tool to derive simultaneously exponent and extremes of power-law distributions
• [C II]-deficit caused by self-absorption in an ionized carbon-filled bubble in RCW79
• Density profile of a self-gravitating polytropic turbulent fluid in a rotating disk near to the cloud core
• Exploring non-thermal emission from the star-forming region NGC 3603 through a realistic modelling of its environment
• Cold atomic gas identified by HI self-absorption. Cold atomic clouds toward giant molecular filaments
• Sub-kpc scale gas density histogram of the Galactic molecular gas: a new statistical method to characterise galactic-scale gas structures
• Linear filament and nested cluster evolution tomography (LANCET) I. Capture the evolution of dense gas in 14-parsec filament G316.8
• From Interstellar Clouds to Stars
• The impact of bars on the properties of HII regions in the TIMER survey
• Density profile of a self-gravitating polytropic turbulent fluid in the context of ensembles of molecular clouds
• Contour Analysis Tool: an interactive tool for background and morphology analysis