Wide-field CO isotopologue emission and the CO-to-H${}_2$ factor across the nearby spiral galaxy M101

Abstract

Carbon monoxide (CO) emission is the most widely used tracer of the bulk molecular gas in the interstellar medium (ISM) in extragalactic studies. The CO-to-H${}_2$ conversion factor, ${\alpha }_{\mathrm{CO}}$, links the observed CO emission to the total molecular gas mass. However, no single prescription perfectly describes the variation of ${\alpha }_{\mathrm{CO}}$ across all environments across galaxies as a function of metallicity, molecular gas opacity, line excitation, and other factors. Using resolved spectral line observations of CO and its isotopologues, we can constrain the molecular gas conditions and link them to a variation in the conversion factor. We present new IRAM 30-m 1mm and 3mm line observations of ${}^{12}$CO, ${}^{13}$CO, and C${}^{18}$O} across the nearby galaxy M101. Based on the CO isotopologue line ratios, we find that selective nucleosynthesis and opacity changes are the main drivers of the variation in the line emission across the galaxy. Furthermore, we estimated ${\alpha }_{\mathrm{CO}(1-0)}$ using different approaches, including (i) the dust mass surface density derived from far-IR emission as an independent tracer of the total gas surface density and (ii) LTE-based measurements using the optically thin ${}^{13}$CO(1-0) intensity. We find an average value of ${\alpha }_{\mathrm{CO}}=4.4\pm 0.9{\mathrm{M}}_{\odot }\mathrm{p}{\mathrm{c}}^{-2}(\mathrm{K}\mathrm{km}{\mathrm{s}}^{-1}{)}^{-1}$ across the galaxy, with a decrease by a factor of 10 toward the 2 kpc central region. In contrast, we find LTE-based values are lower by a factor of 2-3 across the disk relative to the dust-based result. Accounting for ${\alpha }_{\mathrm{CO}}$ variations, we found significantly reduced molecular gas depletion time by a factor 10 in the galaxy's center. In conclusion, our result suggests implications for commonly derived scaling relations, such as an underestimation of the slope of the Kennicutt Schmidt law, if ${\alpha }_{\mathrm{CO}}$ variations are not accounted for.

arXiv commentAccepted for publication in A&A, 25 pages, 15 figures

References in corpus (115)

• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The Infrared Array Camera (IRAC) for the Spitzer Space Telescope
• Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy
• The Spitzer Space Telescope Mission
• The Galaxy Evolution Explorer: A Space Ultraviolet Survey Mission
• The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
• The Herschel-SPIRE instrument and its in-flight performance
• The CO-to-H2 Conversion Factor
• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• The Star Formation Efficiency in Nearby Galaxies: Measuring Where Gas Forms Stars Effectively
• The Star Formation Law in Nearby Galaxies on Sub-Kpc Scales
• A computer program for fast non-LTE analysis of interstellar line spectra
• Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe
• The Sixteenth Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
• THINGS: The HI Nearby Galaxy Survey
• Rotating Nuclear Rings and Extreme Starbursts in Ultraluminous Galaxies
• A General Theory of Turbulence-Regulated Star Formation, From Spirals to ULIRGs
• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• Galactic Chemical Evolution: Hydrogen Through Zinc
• The Dark Molecular Gas
• Molecular Gas and Star Formation in Nearby Disk Galaxies
• The Evolution of the Elemental Abundances in the Gas and Dust Phases of the Galaxy
• HERACLES: The HERA CO-Line Extragalactic Survey
• The CO-to-H2 Conversion Factor and Dust-to-Gas Ratio on Kiloparsec Scales in Nearby Galaxies
• The CO-to-H2 Conversion Factor From Infrared Dust Emission Across the Local Group
• xCOLD GASS: the complete IRAM-30m legacy survey of molecular gas for galaxy evolution studies
• The Spitzer Local Volume Legacy: Survey Description and Infrared Photometry
• The Star Formation Rate and Gas Surface Density Relation in the Milky Way: Implications for Extragalactic Studies
• KINGFISH -- Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel: Survey Description and Image Atlas
• The Composition Gradient in M101 Revisited. II. Electron Temperatures and Implications for the Nebular Abundance Scale
• A Constant Molecular Gas Depletion Time in Nearby Disk Galaxies
• A General Model for the CO-H2 Conversion Factor in Galaxies with Applications to the Star Formation Law
• Star Formation from Galaxies to Globules
• A z=0 Multi-wavelength Galaxy Synthesis I: A WISE and GALEX Atlas of Local Galaxies
• Solar System Abundances of the Elements
• Low CO Luminosities in Dwarf Galaxies
• On the Relationship Between Molecular Hydrogen and Carbon Monoxide Abundances in Molecular Clouds
• Central Rotation Curves of Spiral Galaxies
• Stellar populations dominated by massive stars in dusty starburst galaxies across cosmic time
• The Spitzer Survey of the Small Magellanic Cloud: FIR Emission and Cold Gas in the SMC
• ALMA Reveals the Molecular Medium Fueling the Nearest Nuclear Starburst
• Distances to PHANGS Galaxies: New Tip of the Red Giant Branch Measurements and Adopted Distances
• The Effelsberg-Bonn HI Survey: Milky Way gas. First data release
• Planck intermediate results. XXII. Frequency dependence of thermal emission from Galactic dust in intensity and polarization
• The Plateau de Bure + 30m Arcsecond Whirlpool Survey reveals a thick disk of diffuse molecular gas in the M51 galaxy
• CHAOS I: Direct Chemical Abundances for HII Regions in NGC 628
• Molecular gas in extreme star-forming environments: the starbursts Arp220 and NGC6240 as case studies
• Planck intermediate results. XVII. Emission of dust in the diffuse interstellar medium from the far-infrared to microwave frequencies
• Dust and Gas in the Magellanic Clouds from the HERITAGE Herschel Key Project. I. Dust Properties and Insights into the Origin of the Submm Excess Emission
• Molecular Gas Properties on Cloud Scales Across the Local Star-forming Galaxy Population
• Cloud Scale ISM Structure and Star Formation in M51
• CHAOS III: Gas-Phase Abundances in NGC5457
• CHAOS IV: Gas-Phase Abundance Trends From The First Four CHAOS Galaxies
• Planck early results. XXI. Properties of the interstellar medium in the Galactic plane
• The On The Fly Imaging Technique
• EMPIRE: The IRAM 30-m Dense Gas Survey of Nearby Galaxies
• Radial distribution of dust, stars, gas, and star-formation rate in DustPedia face-on galaxies
• Dust and Gas in the Magellanic Clouds from the HERITAGE Herschel Key Project. II. Gas-to-Dust Ratio Variations across ISM Phases
• New Constraints on the ${}^{12}$CO(2-1)/(1-0) Line Ratio Across Nearby Disc Galaxies
• A Mapping Survey of the 12CO and 13CO Emission in Galaxies
• Kinematics of Spiral Arm Streaming in M51
• Molecular Cloud Populations in the Context of Their Host Galaxy Environments: A Multiwavelength Perspective
• Low-J CO Line Ratios From Single Dish CO Mapping Surveys and PHANGS-ALMA
• Is atomic carbon a good tracer of molecular gas in metal-poor galaxies?
• The Panchromatic Hubble Andromeda Treasury VIII: A Wide-Area, High-Resolution Map of Dust Extinction in M31
• Physical Properties of Molecular Clouds at 2 parsec Resolution in the Low-Metallicity Dwarf Galaxy NGC 6822 and the Milky Way
• Molecular gas in low-metallicity starburst galaxies: Scaling relations and the CO-to-H${}_2$ conversion factor
• Galactic interstellar 18O/17O ratios - a radial gradient?
• Distribution and mass of diffuse and dense CO gas in the Milky Way
• Millimeter-Wave Line Ratios and Sub-beam Volume Density Distributions
• Dust Emissivity Variations In the Milky Way
• The environmental dependence of the X_CO conversion factor
• Full-disc ${}^{13}$CO(1-0) mapping across nearby galaxies of the EMPIRE survey and the CO-to-H${}_2$ conversion factor
• Physical Conditions in Molecular Clouds in the Arm and Interarm Regions of M51
• CI and CO in nearby galaxy centers: the bright galaxies NGC1068 (M77), NGC2146, NGC3079, NGC4826 (M64), and NGC7469
• The EDGE-CALIFA survey: Variations in the Molecular Gas Depletion Time in Local Galaxies
• A Survey of the Molecular ISM Properties of Nearby Galaxies using the Herschel FTS
• The Chemical Composition and Gas-to-Dust Mass Ratio of Nearby Interstellar Matter
• The final data release of ALLSMOG: a survey of CO in typical local low-M* star-forming galaxies
• Dynamically Influenced Molecular Clouds in the Nucleus of NGC 6946: Variations in the CO Isotopic Line Ratios
• CO Multi-line Imaging of Nearby Galaxies (COMING). IX. ${}^{12}$CO($J$=2-1)/${}^{12}$CO($J$=1-0) line ratio on kiloparsec scales
• Using CO line ratios to trace the physical properties of molecular clouds
• CI and CO in nearby galaxy centers. The star-burst galaxies NGC 278, NGC 660, NGC 3628, NGC 4631, and NGC 4666
• Kinematics of the Atomic ISM in M33 on 80 pc scales
• Central molecular zones in galaxies: 12CO-to-13CO ratios, carbon budget, and X factors
• An Empirical Determination of the Dust Mass Absorption Coefficient, ${\kappa }_d$, Using the Herschel Reference Survey
• The First Maps of ${\kappa }_d$ -- the Dust Mass Absorption Coefficient -- in Nearby Galaxies, with DustPedia
• Molecular Gas Properties and CO-to-H2 Conversion Factors in the Central Kiloparsec of NGC 3351
• ${}^{13}$CO/C${}^{18}$O Gradients Across the Disks of Nearby Spiral Galaxies
• Resolving CO (2-1) in z~1.6 Gas-Rich Cluster Galaxies with ALMA: Rotating Molecular Gas Disks with Possible Signatures of Gas Stripping
• Ultraviolet Signatures of Tidal Interaction in the Giant Spiral Galaxy, M101
• How well does CO emission measure the H${}_2$ mass of MCs?
• Detection of the ^3P_2 - ^3P_1 Submillimeter Transition of 13CI in the Interstellar Medium: Implication for Chemical Fractionation
• The Spatially Resolved Dust-to-Metals Ratio in M101
• Extreme CO Isotopic Abundances in the ULIRG IRAS 13120-5453: An Extremely Young Starburst or Top-Heavy Initial Mass Function
• Are local ULIRGs powered by AGN? The sub-kpc view of the 220 GHz continuum. PUMA II
• ALMA view of the ${}^{12}$C/${}^{13}$C isotopic ratio in starburst galaxies
• Systematic variation of the 12CO/13CO ratio as a function of star-formation rate surface density
• C18O, 13CO, and 12CO abundances and excitation temperatures in the Orion B molecular cloud: An analysis of the precision achievable when modeling spectral line within the Local Thermodynamic Equilibrium approximation
• Extreme CO Isotopologue Line Ratios in ULIRGS: Evidence for a top-heavy IMF
• Scaling relations of the properties for CO resolved structures in nearby spiral galaxies
• Evidence of boosted 13CO/12CO ratio in early-type galaxies in dense environments
• 12CO, 13CO and C18O observations along the major axes of nearby bright infrared galaxies
• The JCMT Nearby Galaxies Legacy Survey -- XI. -- Environmental Variations in the Atomic and Molecular Gas Radial Profiles of Nearby Spiral Galaxies
• A 2-3 mm high-resolution molecular line survey towards the centre of the nearby spiral galaxy NGC 6946
• A CO isotopologue Line Atlas within the Whirlpool galaxy Survey (CLAWS)
• Molecular Gas and Star Formation in NGC 3077
• Determining the Co-Rotation Radii of Spiral Galaxies Using Spiral Arm Pitch Angle Measurements at Multiple Wavelengths
• A simple approach to CO cooling in molecular clouds
• PdBI U/LIRG Survey (PULS): Dense Molecular Gas in Arp 220 and NGC 6240
• Benchmarking Dust Emission Models in M101
• CARMA Survey toward Infrared-bright Nearby Galaxies (STING). IV. Spatially Resolved 13CO in Spiral Galaxies
• The Lyman Alpha Reference Sample XI: Efficient Turbulence Driven Lyα Escape and the Analysis of IR, CO and [C II]158 μm
• A High-Resolution, Dust-Selected Molecular Cloud Catalogue of M33, the Triangulum Galaxy
• A SOFIA Survey of [CII] in the galaxy M51 II. [CII] and CO kinematics across spiral arms

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• The Arizona Molecular ISM Survey with the SMT: Variations in the CO(2-1)/CO(1-0) Line Ratio Across the Galaxy Population
• Molecular Cloud Matching in CO and Dust in M33 I. High-Resolution Hydrogen Column Density Maps from Herschel
• CO-to-H${}_2$ conversion factor and grain size distribution through the analysis of ${\alpha }_{\mathrm{CO}}$-$q_{\mathrm{PAH}}$ relation
• Dust and gas modelling in radiative transfer simulations of disc-dominated galaxies with RADMC-3D