Bias-free Measurement of Giant Molecular Cloud Properties

Abstract

(abridged) We review methods for measuring the sizes, line widths, and luminosities of giant molecular clouds (GMCs) in molecular-line data cubes with low resolution and sensitivity. We find that moment methods are robust and sensitive -- making full use of both position and intensity information -- and we recommend a standard method to measure the position angle, major and minor axis sizes, line width, and luminosity using moment methods. Without corrections for the effects of beam convolution and sensitivity to GMC properties, the resulting properties may be severely biased. This is particularly true for extragalactic observations, where resolution and sensitivity effects often bias measured values by 40% or more. We correct for finite spatial and spectral resolutions with a simple deconvolution and we correct for sensitivity biases by extrapolating properties of a GMC to those we would expect to measure with perfect sensitivity. The resulting method recovers the properties of a GMC to within 10% over a large range of resolutions and sensitivities, provided the clouds are marginally resolved with a peak signal-to-noise ratio greater than 10. We note that interferometers systematically underestimate cloud properties, particularly the flux from a cloud. The degree of bias depends on the sensitivity of the observations and the (u,v) coverage of the observations. In the Appendix to the paper we present a conservative, new decomposition algorithm for identifying GMCs in molecular-line observations. This algorithm treats the data in physical rather than observational units, does not produce spurious clouds in the presence of noise, and is sensitive to a range of morphologies. As a result, the output of this decomposition should be directly comparable among disparate data sets.

Accepted to PASP (19 pgs., 12 figures). The submission describes an IDL software package available from http://cfa-www.harvard.edu/~erosolow/cprops/

Cited by in corpus (143)

• Structural Analysis of Molecular Clouds: Dendrograms
• The Resolved Properties of Extragalactic Giant Molecular Clouds
• Physical properties of molecular clouds for the entire Milky Way disk
• The lifecycle of molecular clouds in nearby star-forming disc galaxies
• Fast and inefficient star formation due to short-lived molecular clouds and rapid feedback
• ALMA Reveals the Molecular Medium Fueling the Nearest Nuclear Starburst
• PHANGS-ALMA Data Processing and Pipeline
• Giant Molecular Cloud Catalogues for PHANGS-ALMA: Methods and Initial Results
• Molecular Gas Properties on Cloud Scales Across the Local Star-forming Galaxy Population
• The molecular cloud lifecycle
• Molecular Cloud Populations in the Context of Their Host Galaxy Environments: A Multiwavelength Perspective
• A Portrait of Cold Gas in Galaxies at 60pc Resolution and a Simple Method to Test Hypotheses That Link Small-Scale ISM Structure to Galaxy-Scale Processes
• Low-J CO Line Ratios From Single Dish CO Mapping Surveys and PHANGS-ALMA
• ALMA Observations of the Antennae Galaxies: I. A New Window on a Prototypical Merger
• Giant Molecular Clouds in M31: I - Molecular Cloud Properties
• 'The Brick' is not a brick: A comprehensive study of the structure and dynamics of the Central Molecular Zone cloud G0.253+0.016
• Triggered star formation on the borders of the Galactic HII region RCW 82
• AUTO-MULTITHRESH: A General Purpose Automasking Algorithm
• The SEDIGISM survey: first data release and overview of the Galactic structure
• Star Formation Relations in the Milky Way
• Physical Properties of Molecular Clouds at 2 parsec Resolution in the Low-Metallicity Dwarf Galaxy NGC 6822 and the Milky Way
• Short GMC lifetimes: an observational estimate with the PdBI Arcsecond Whirlpool Survey (PAWS)
• The Structure of a Low-Metallicity Giant Molecular Cloud Complex
• The Physical Conditions in a Pre Super Star Cluster Molecular Cloud in the Antennae Galaxies
• The integrated properties of the molecular clouds from the JCMT CO(3-2) High Resolution Survey
• Giant Molecular Clouds in the Early-Type Galaxy NGC4526
• Investigating the structure and fragmentation of a highly filamentary IRDC
• Dense gas is not enough: environmental variations in the star formation efficiency of dense molecular gas at 100pc scales in M51
• Molecular line mapping of the giant molecular cloud associated with RCW 106 - III. Multi-molecular line mapping
• Molecular line mapping of the giant molecular cloud associated with RCW 106 - II. Column density and dynamical state of the clumps
• The PdBI Arcsecond Whirlpool Survey (PAWS). The Role of Spiral Arms in Cloud and Star Formation
• Very Deep Inside the SN 1987A Core Ejecta: Molecular Structures Seen in 3D
• Dissecting the molecular structure of the Orion B cloud: Insight from Principal Component Analysis
• The role of galactic dynamics in shaping the physical properties of giant molecular clouds in Milky Way-like galaxies
• The Molecular Interstellar Medium of the Local Group Dwarf NGC6822
• The Mass-Size Relation and the Constancy of GMC Surface Densities in the Milky Way
• Evolution of giant molecular clouds across cosmic time
• CARMA Large Area Star Formation Survey: Project Overview with Analysis of Dense Gas Structure and Kinematics in Barnard 1
• WISDOM Project -- IX Giant Molecular Clouds in the Lenticular Galaxy NGC4429: Effects of Shear and Tidal Forces on Clouds
• The headlight cloud in NGC 628: An extreme giant molecular cloud in a typical galaxy disk
• Comparative Analysis of Molecular Clouds in M31, M33 and the Milky Way
• The core population and kinematics of a massive clump at early stages: an ALMA view
• The Circumnuclear Disk Revealed by ALMA. I. Dense Clouds and Tides in the Galactic Center
• Mass Functions of Giant Molecular Clouds and Young Star Clusters in Six Nearby Galaxies
• Dense molecular gas properties on 100 pc scales across the disc of NGC 3627
• The ALMOND Survey: Molecular cloud properties and gas density tracers across 25 nearby spiral galaxies with ALMA
• Identification of prestellar cores in high-mass star forming clumps via ${\mathrm{H}}_2{\mathrm{D}}^{+}$ observations with ALMA
• A statistical study of giant molecular clouds traced by ${}^{13}$CO, C${}^{18}$O, CS, and CH${}_3$OH in the disk of NGC 1068 based on ALMA observations
• 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<$0°
• ALMA Observations of a Quiescent Molecular Cloud in the Large Magellanic Cloud
• The Mopra Southern Galactic Plane CO Survey - Data Release 1
• Simulations of the star-forming molecular gas in an interacting M51-like galaxy: cloud population statistics
• Kiloparsec-scale Variations in the Star Formation Efficiency of Dense Gas: the Antennae Galaxies (NGC 4038/39)
• Rotation of molecular clouds in M~51
• Molecular scale height in spiral galaxies
• The JCMT Gould Belt Survey: Evidence for radiative heating in Serpens MWC 297 and its influence on local star formation
• Methanol masers in NGC 253 with ALCHEMI
• The Molecular Clouds Fueling a 1/5 Solar Metallicity Starburst
• A large amount of diffuse molecular gases in the bar of the strongly barred galaxy NGC1300: Cause of the low star formation efficiency
• Mapping molecular emission in Vela Molecular Ridge Cloud D
• A 2-3 mm high-resolution molecular line survey towards the centre of the nearby spiral galaxy NGC 6946
• Molecular Clouds in the Second Quadrant of the Milky Way Mid-plane from l$=$104$.{}^{\circ }$75 to l=119$.{}^{\circ }$75 and b=$-$5$.{}^{\circ }$25 to b=5$.{}^{\circ }$25
• From Gas to Stars in Energetic Environments: Dense Gas Clumps in the 30 Doradus Region Within the Large Magellanic Cloud
• Are massive dense clumps truly sub-virial? A new analysis using Gould Belt ammonia data
• PHANGS: Constraining Star Formation Timescales Using the Spatial Correlations of Star Clusters and Giant Molecular Clouds
• The SEDIGISM survey: The influence of spiral arms on the molecular gas distribution of the inner Milky Way
• Two physical regimes for the Giant HII Regions and Giant Molecular Clouds in the Antennae Galaxies
• Comparing the Properties of GMCs in M33 from Simulations and Observations
• Properties of giant molecular clouds in the strongly barred galaxy NGC1300
• PHANGS-JWST First Results: Stellar Feedback-Driven Excitation and Dissociation of Molecular Gas in the Starburst Ring of NGC 1365?
• Multi-Scale Stellar Associations across the Star Formation Hierarchy in PHANGS-HST Nearby Galaxies: Methodology and Properties
• Molecular cloud catalogue from ${}^{13}$CO(1-0) data of the Forgotten Quadrant Survey
• Structural and Dynamical Analysis of 0.1pc Cores and Filaments in the 30~Doradus-10 Giant Molecular Cloud
• OGHReS: Large-scale filaments in the outer Galaxy
• CO(2-1) Survey at 9 parsec resolution in the SMC
• Multiwavelength investigation of the candidate Galactic PeVatron MGRO J1908+06
• Kinematic analysis of the super-extended HI disk of the nearby spiral galaxy M83
• The SEDIGISM survey: Molecular cloud morphology. I. Classification and star formation
• HI Clouds in LITTLE THINGS Dwarf Irregular Galaxies
• CO Excitation and its Connection to Star Formation at 200 pc in NGC 1365
• DeGaS-MC: Dense Gas Survey in the Magellanic Clouds I -- An APEX survey of HCO+ and HCN(2-1) toward the LMC and SMC
• WISDOM Project -- XV. Giant Molecular Clouds in the Central Region of the Barred Spiral Galaxy NGC 5806
• Deep learning denoising by dimension reduction: Application to the ORION-B line cubes
• Probing the Cold Deep Depths of the California Molecular Cloud: The Icy Relationship between CO and Dust
• ALMA Resolves Giant Molecular Clouds in a Tidal Dwarf Galaxy
• Formation of hub-filament structure triggered by cloud-cloud collision in W33 complex
• WISDOM Project XII. Clump properties and turbulence regulated by clump-clump collisions in the dwarf galaxy NGC404
• An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. II. CO Cloud Catalog
• On the Beam Filling Factors of Molecular Clouds
• Stellar encounters with giant molecular clouds
• ALMA CO(3-2) Observations of Star-Forming Filaments in a Gas-Poor Dwarf Spheroidal Galaxy
• PHANGS-ALMA: Arcsecond CO(2-1) Imaging of Nearby Star-Forming Galaxies
• WISDOM project -- XI. Star Formation Efficiency in the Bulge of the AGN-host Galaxy NGC 3169 with SITELLE and ALMA
• Connection among environment, cloud-cloud collision speed, and star formation activity in the strongly barred galaxy NGC1300
• CO(2-1)/CO(1-0) line ratio on $\sim$100 parsec scale in the nearby barred galaxy NGC1300
• Turbulence and Accretion: a High-resolution Study of the B5 Filaments
• FacetClumps: A Facet-based Molecular Clump Detection Algorithm
• High resolution LAsMA ${}^{12}$CO and ${}^{13}$CO observation of the G305 giant molecular cloud complex : II. Effect of feedback on clump properties
• Identification of molecular clouds in emission maps: a comparison between methods in the \ce{^{13}CO}/\ce{C^{18}O} ($J=3-2$) Heterodyne Inner Milky Way Plane Survey
• High-resolution APEX/LAsMA ${}^{12}$CO and ${}^{13}$CO (3-2) observation of the G333 giant molecular cloud complex : II. Survival and gravitational collapse of dense gas structures under feedback
• Pre-supernova feedback mechanisms drive the destruction of molecular clouds in nearby star-forming disc galaxies
• Resolved star formation in the metal poor star-forming region Magellanic Bridge C
• Low star formation efficiency due to turbulent adiabatic compression in the Taffy bridge
• Extreme giant molecular clouds in the luminous infrared galaxy NGC 3256
• CI and CO in Nearby Spiral Galaxies -- I. Line Ratio and Abundance Variations at ~ 200 pc Scales
• ACA CO($J=2-1$) Mapping of the Nearest Spiral Galaxy M33. I. Initial Results and Identification of Molecular Clouds
• The SEDIGISM survey: Molecular cloud morphology. II. Integrated source properties
• The PHANGS-MUSE/HST-Halpha Nebulae Catalogue
• The impact of HII regions on Giant Molecular Cloud properties in nearby galaxies sampled by PHANGS ALMA and MUSE
• The initial conditions for young massive cluster formation in the Galactic Centre: convergence of large-scale gas flows
• Does the HCN/CO ratio trace the star-forming fraction of gas? I. A comparison with analytical models of star formation
• A sensitive, high-resolution, wide-field IRAM NOEMA CO(1-0) survey of the very nearby spiral galaxy IC 342
• On the Spatial Distribution of ${}^{13}$CO Structures within ${}^{12}$CO Molecular Clouds
• Local starburst conditions and formation of GRB 980425 / SN 1998bw within a collisional ring
• Exhaustion of the gas next to M31's supermassive black hole
• Kinematics of the ionized and molecular gas in nearby luminous infrared interacting galaxies
• Oumuamuas passing through molecular clouds
• Cold molecular gas in the hot nuclear wind of the Milky Way
• A Large Molecular Gas Reservoir in the Protocluster SPT2349$-$56 at $z=4.3$
• A Giant Molecular Cloud Catalog in the Molecular Disk of the Elliptical Galaxy NGC 5128 (Centaurus A)
• Giant molecular clouds and their Type classification in M74: Toward understanding star formation and cloud evolution
• The G332 molecular cloud ring: I. Morphology and physical characteristics
• M31 circum-nuclear region: a molecular survey with the IRAM-interferometer
• ALMA resolves molecular clouds in the metal poor Magellanic Bridge A
• A census of young stellar objects in two line-of-sight star forming regions toward IRAS 22147+5948 in the outer Galaxy
• Anisotropy of random motions of gas in Messier 33
• ACA CO(J=2-1) Mapping of the Nearest Spiral Galaxy M33. II. Exploring the Evolution of Giant Molecular Clouds
• ALMA ${}^{13}\mathrm{CO}$(J=1-0) Observations of NGC 604 in M33: Physical Properties of Molecular Clouds
• SuperCAM CO(3-2) APEX survey at 6 pc resolution in the Small Magellanic Clouds
• The Hierarchical Dynamical State of Molecular Gas from 3 to 300 pc in NGC 253
• Does the HCN/CO ratio trace the star-forming fraction of gas? II. Variations in CO and HCN Emissivity
• CO-CHANGES II: spatially resolved IRAM 30M CO line observations of 23 nearby edge-on spiral galaxies
• Bright [CII]158$\mu$m Streamers as a Beacon for Giant Galaxy Formation in SPT2349$-$56 at $z=4.3$
• Dense clumps survive in the vicinity of R136 in 30 Doradus
• Molecular cloud matching in CO and dust in M33 II. Physical properties of giant molecular clouds
• Sub-kpc scale gas density histogram of the Galactic molecular gas: a new statistical method to characterise galactic-scale gas structures
• Examinations of CO completeness based on three independent CO surveys
• Systematic Investigation of Dust and Gaseous CO in 12 Nearby Molecular Clouds
• Kinematics and Feedback in H II regions in the Dwarf Starburst Galaxy IC 10
• CO Observations of the SMC-N66 Hii Region with ALMA: Properties of Clumps along Filamentary Molecular Clouds and Possible Expansion Motion
• Molecular Clouds at the Edge of the Galaxy II. Physical properties and scaling relations
• Star Formation at the Periphery of a Molecular Superbubble: The Case of G12.79+0.43
• Contour Analysis Tool: an interactive tool for background and morphology analysis