Gas Column Density Distribution of Molecular Clouds in the Third Quadrant of the Milky Way

Abstract

We have obtained column density maps for an unbiased sample of 120 molecular clouds in the third quadrant of the Milky Way mid-plane (b$\le |5{|}^{\circ }$) within the galactic longitude range from 195${}^{\circ }$ to 225${}^{\circ }$, using the high sensitivity ${}^{12}$CO and ${}^{13}$CO ($J=1-0$) data from the Milky Way Imaging Scroll Painting (MWISP) project. The probability density functions of the molecular hydrogen column density of the clouds, N-PDFs, are fitted with both log-normal (LN) function and log-normal plus power-law (LN+PL) function. The molecular clouds are classified into three categories according to their shapes of N-PDFs, i.e., LN, LN+PL, and UN (unclear), respectively. About 72\% of the molecular clouds fall into the LN category, while 18\% and 10\% into the LN+PL and UN categories, respectively. A power-law scaling relation, ${\sigma }_s\propto N_{H_2}^{0.44}$, exists between the width of the N-PDF, ${\sigma }_s$, and the average column density, $N_{H_2}$, of the molecular clouds. However, ${\sigma }_s$ shows no correlation with the mass of the clouds. A correlation is found between the dispersion of normalized column density, ${\sigma }_{N/<\mathrm{N}>}$, and the sonic Mach number, $\mathcal{M}$, of molecular clouds. Overall, as predicted by numerical simulations, the N-PDFs of the molecular clouds with active star formation activity tend to have N-PDFs with power-law high-density tails.

References in corpus (62)

• emcee: The MCMC Hammer
• Theory of Star Formation
• The Milky Way in Molecular Clouds: A New Complete CO Survey
• Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way
• A General Theory of Turbulence-Regulated Star Formation, From Spirals to ULIRGs
• 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
• MAMBO Mapping of Spitzer c2d Small Clouds and Cores
• Analytical theory for the initial mass function: CO clumps and prestellar cores
• The Universality of the Stellar IMF
• The Density Probability Distribution in Compressible Isothermal Turbulence: Solenoidal versus Compressive Forcing
• The Star Formation Rate of Supersonic MHD Turbulence
• Probing the evolution of molecular cloud structure: From quiescence to birth
• The WISE Catalog of Galactic HII Regions
• On the Star Formation Efficiency of Turbulent Magnetized Clouds
• Physical properties of molecular clouds for the entire Milky Way disk
• The Equilibrium State of Molecular Regions in the Outer Galaxy
• What determines the density structure of molecular clouds ? A case study of Orion B with Herschel
• The relation between gas and dust in the Taurus Molecular Cloud
• On the Density Distribution in Star-forming Interstellar Clouds
• A Large Catalog of Accurate Distances to Local Molecular Clouds: The Gaia DR2 Edition
• Markov Chain Monte Carlo Methods for Bayesian Data Analysis in Astronomy
• A revised catalogue of 294 Galactic supernova remnants
• 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
• The Milky Way Imaging Scroll Painting (MWISP): Project Details and Initial Results from the Galactic Longitude of 25.8deg to 49.7deg
• A Classification Scheme for Young Stellar Objects Using the WIDE-FIELD INFRARED SURVEY EXPLORER AllWISE Catalog: Revealing Low-Density Star Formation in the Outer Galaxy
• A Uniform Catalog of Molecular Clouds in the Milky Way
• 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
• High-dynamic-range extinction mapping of infrared dark clouds: Dependence of density variance with sonic Mach number in molecular clouds
• The density variance -- Mach number relation in supersonic, isothermal turbulence
• An all-sky Support Vector Machine selection of WISE YSO Candidates
• Molecular clouds have power-law probability distribution functions
• The Star Formation Rate in the Gravoturbulent Interstellar Medium
• Analytical theory for the initial mass function: III time dependence and star formation rate
• A method for reconstructing the variance of a 3D physical field from 2D observations: Application to turbulence in the ISM
• Detection of two power-law tails in the probability distribution functions of massive GMCs
• The Column Density Variance-Sonic Mach Number Relationship
• Identification of Young Stellar Object candidates in the $Gaia$ DR2 x AllWISE catalogue with machine learning methods
• Understanding star formation in molecular clouds II. Signatures of gravitational collapse of IRDCs
• The Density Variance Mach Number Relation in the Taurus Molecular Cloud
• Does External Pressure Explain Recent Results for 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
• A large catalogue of molecular clouds with accurate distances within 4 kpc of the Galactic disk
• Connection between dense gas mass fraction, turbulence driving, and star formation efficiency of molecular clouds
• Large scale IRAM 30m CO-observations in the giant molecular cloud complex W43
• Evolving Molecular Cloud Structure and the Column Density Probability Distribution Function
• Distances and statistics of local molecular clouds in the first Galactic quadrant
• Evolution of the density PDF in star forming clouds: the role of gravity
• The Forgotten Quadrant Survey. ${}^{12}$CO and ${}^{13}$CO (1-0) survey of the Galactic Plane in the range 220°$<l<$240° -2.5°$<b<$0°
• On the turbulence driving mode of expanding HII regions
• Relationship between turbulence energy and density variance in the Solar neighbourhood molecular clouds
• A large-scale survey of CO and its isotopologues toward the Rosette molecular cloud
• Molecular cloud distances based on the MWISP CO survey and Gaia DR2
• Bird's eye view of molecular clouds in the Milky Way: I. Column density and star formation from sub-pc to kpc scales
• A Morphological Classification of 18190 Molecular Clouds Identified in ${}^{12}$CO Data from the MWISP Survey
• 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
• The Column Density Structure of Orion A Depicted by N-PDF
• A Large-field J=1-0 Survey of CO and Its Isotopologues Toward the Cassiopeia A Supernova Remnant

Cited by in corpus (11)

• PDFchem: A new fast method to determine ISM properties and infer environmental parameters using probability distributions
• Cloud properties across spatial scales in simulations of the interstellar medium
• Metallicity dependence of the CO-to-H${}_2$ and the [CI]-to-H${}_2$ conversion factors in galaxies
• 25 years of XMM-Newton observations of the Sgr A complex: 3D distribution and internal structure of the clouds
• On the Spatial Distribution of ${}^{13}$CO Structures within ${}^{12}$CO Molecular Clouds
• Multi log-normal density structure in Cygnus-X molecular clouds: A fitting for N-PDF without power-law
• Molecular Clouds in the Galactic Plane from $l$ = [59.75${}^{\circ }$, 74.75${}^{\circ }$] and $b$ = [$-$5.25${}^{\circ }$, +5.25${}^{\circ }$]
• Examining Turbulence in Galactic Molecular Clouds -- I: A Statistical Analysis of Velocity Structures
• Sub-kpc scale gas density histogram of the Galactic molecular gas: a new statistical method to characterise galactic-scale gas structures
• Molecular Clouds at the Edge of the Galaxy II. Physical properties and scaling relations
• Contour Analysis Tool: an interactive tool for background and morphology analysis