Sub-kpc scale gas density histogram of the Galactic molecular gas: a new statistical method to characterise galactic-scale gas structures

Abstract

To understand physical properties of the interstellar medium (ISM) on various scales, we investigate it at parsec resolution on the kiloparsec scale. Here, we report on the sub-kpc scale Gas Density Histogram (GDH) of the Milky Way. The GDH is a density probability distribution function (PDF) of the gas volume density. Using this method, we are free from an identification of individual molecular clouds and their spatial structures. We use survey data of ${}^{12}$CO and ${}^{13}$CO ($J$=1-0) emission in the Galactic plane ($l=10^{\circ }$-$50^{\circ }$) obtained as a part of the FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45m telescope (FUGIN). We make a GDH for every channel map of $2^{\circ }\times 2^{\circ }$ area, including the blank sky component, and without setting cloud boundaries. This is a different approach from previous works for molecular clouds. The GDH fits well to a single or double log-normal distribution, which we name the low-density log-normal (L-LN) and high-density log-normal (H-LN) components, respectively. The multi-log-normal components suggest that the L-LN and H-LN components originate from two different stages of structure formation in the ISM. Moreover, we find that both the volume ratios of H-LN components to total ($f_{\mathrm{H}}$) and the width of the L-LN along the gas density axis (${\sigma }_{\mathrm{L}}$) show coherent structure in the Galactic-plane longitude-velocity diagram. It is possible that these GDH parameters are related to strong galactic shocks and other weak shocks in the Milky Way.

References in corpus (31)

• Array Programming with NumPy
• Trigonometric Parallaxes Of High-Mass Star Forming Regions: Our View Of The Milky Way
• Structural Analysis of Molecular Clouds: Dendrograms
• Bias-free Measurement of Giant Molecular Cloud Properties
• CO Isotopologues in the Perseus Molecular Cloud Complex: the X-Factor and Regional Variations
• What determines the density structure of molecular clouds ? A case study of Orion B with Herschel
• FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope (FUGIN) I: Project Overview and Initial Results
• Giant Molecular Cloud Catalogues for PHANGS-ALMA: Methods and Initial Results
• Evolution of column density distributions within Orion~A
• Understanding star formation in molecular clouds I. Effects of line-of-sight contamination on the column density structure
• ATLASGAL-selected massive clumps in the inner Galaxy: I. CO depletion and isotopic ratios
• 2MASS wide field extinction maps: II. The Ophiuchus and the Lupus cloud complexe
• Prospecting in Ultracool Dwarfs: Measuring the Metallicities of Mid- and Late-M Dwarfs
• Millimeter-Wave Line Ratios and Sub-beam Volume Density Distributions
• The Molecular Properties of Galactic HII Regions
• The shapes of column density PDFs - The importance of the last closed contour
• Density probability distribution functions of diffuse gas in the Milky Way
• Star formation efficiency in the Barred Spiral Galaxy NGC 4303
• Understanding star formation in molecular clouds IV. Column density PDFs from quiescent to massive molecular clouds
• A fundamental test for stellar feedback recipes in galaxy simulations
• CO excitation, molecular gas density and interstellar radiation field in local and high-redshift galaxies
• Evolving Molecular Cloud Structure and the Column Density Probability Distribution Function
• Technique for separating velocity and density contributions in spectroscopic data and its application to studying turbulence and magnetic fields
• Temperature structure and kinematics of the IRDC G035.39-00.33
• The density structure of supersonic self-gravitating turbulence
• Power-law tails in probability density functions of molecular cloud column density
• Structural Variation of Molecular Gas in the Sagittarius Arm and Inter-Arm Regions
• Bird's eye view of molecular clouds in the Milky Way: I. Column density and star formation from sub-pc to kpc scales
• Diverse Molecular Structures Across The Whole Star-Forming Disk of M83: High fidelity Imaging at 40pc Resolution
• Internal Structures of Molecular Clouds in the LMC Revealed by ALMA
• Multi log-normal density structure in Cygnus-X molecular clouds: A fitting for N-PDF without power-law