CO-to-H${}_2$ conversion factor and grain size distribution through the analysis of ${\alpha }_{\mathrm{CO}}$-$q_{\mathrm{PAH}}$ relation

Abstract

The CO-to-H${}_2$ conversion factor (${\alpha }_{\mathrm{CO}}$) is expected to vary with dust abundance and grain size distribution through the efficiency of shielding gas from CO-dissociation radiation. We present a comprehensive analysis of ${\alpha }_{\mathrm{CO}}$ and grain size distribution for nearby galaxies, using the PAH fraction ($q_{\mathrm{PAH}}$) as an observable proxy of grain size distribution. We adopt the resolved observations at 2-kpc resolution in 42 nearby galaxies, where ${\alpha }_{\mathrm{CO}}$ is derived from measured metallicity and surface densities of dust and HI assuming a fixed dust-to-metals ratio. We use an analytical model for the evolution of H${}_2$ and CO, in which the evolution of grain size distribution is controlled by the dense gas fraction ($\eta$). We find that the observed level of $q_{\mathrm{PAH}}$ is consistent with the diffuse-gas-dominated model ($\eta =0.2$) where dust shattering is more efficient. Meanwhile, the slight decreasing trend of observed $q_{\mathrm{PAH}}$ with metallicity is more consistent with high-$\eta$ predictions, likely due to the more efficient loss of PAHs by coagulation. We discuss how grain size distribution (indicated by $q_{\mathrm{PAH}}$) and metallicity impact ${\alpha }_{\mathrm{CO}}$; we however did not obtain conclusive evidence that the grain size distribution affects ${\alpha }_{\mathrm{CO}}$. Observations and model predictions show similar anti-correlation between ${\alpha }_{\mathrm{CO}}$ and 12+log(O/H). Meanwhile, there is a considerable difference in how resolved ${\alpha }_{\mathrm{CO}}$ behaves with $q_{\mathrm{PAH}}$. The observed ${\alpha }_{\mathrm{CO}}$ has a positive correlation with $q_{\mathrm{PAH}}$, while the model-predicted ${\alpha }_{\mathrm{CO}}$ does not have a definite correlation with $q_{\mathrm{PAH}}$. This difference is likely due to the limitation of one-zone treatment in the model.

12 pages, 7 figures, accepted for publication in MNRAS

References in corpus (84)

• Astropy: A Community Python Package for Astronomy
• The chemical composition of the Sun
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy
• The Galaxy Evolution Explorer: A Space Ultraviolet Survey Mission
• The CO-to-H2 Conversion Factor
• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• THINGS: The HI Nearby Galaxy Survey
• Dust Masses, PAH Abundances, and Starlight Intensities in the SINGS Galaxy Sample
• The Mid-Infrared Spectrum of Star-Forming Galaxies: Global Properties of PAH Emission
• High-Resolution Rotation Curves and Galaxy Mass Models from THINGS
• HyperLEDA. III. The catalogue of extragalactic distances
• The Dark Molecular Gas
• 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
• A Molecular Star Formation Law in the Atomic Gas Dominated Regime in Nearby Galaxies
• A characteristic oxygen abundance gradient in galaxy disks unveiled with CALIFA
• Andromeda's Dust
• Planck Early Results: All sky temperature and dust optical depth from Planck and IRAS: Constraints on the "dark gas" in our galaxy
• New calibrations for abundance determinations in HII regions
• A z=0 Multi-wavelength Galaxy Synthesis I: A WISE and GALEX Atlas of Local Galaxies
• The PHANGS-MUSE survey -- Probing the chemo-dynamical evolution of disc galaxies
• Low CO Luminosities in Dwarf Galaxies
• On the Relationship Between Molecular Hydrogen and Carbon Monoxide Abundances in Molecular Clouds
• The Interstellar dust properties of nearby galaxies
• The molecular gas in Luminous Infrared Galaxies I: CO lines, extreme physical conditions, and their drivers
• Nobeyama CO Atlas of Nearby Spiral Galaxies: Distribution of Molecular Gas in Barred and Non-barred Spiral Galaxies
• The Westerbork Hydrogen Accretion in Local Galaxies (HALOGAS) Survey I. Survey Description and Pilot Observations
• Tracing the total molecular gas in galaxies: [CII] and the CO-dark gas
• 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 and Atomic Gas in the Local Group Galaxy M33
• Linking dust emission to fundamental properties in galaxies: The low-metallicity picture
• The CO-H2 Conversion Factor in Disc Galaxies and Mergers
• PHANGS CO kinematics: disk orientations and rotation curves at 150 pc resolution
• Radial distribution of stars, gas and dust in SINGS galaxies. I. Surface photometry and morphology
• Deriving a multivariate CO-to-H${}_2$ conversion function using the [CII]/CO(1-0) ratio and its application to molecular gas scaling relations
• What determines the grain size distribution in galaxies?
• Dynamical Equilibrium in the Molecular ISM in 28 Nearby Star-Forming Galaxies
• Shattering and coagulation of dust grains in interstellar turbulence
• The X-factor in Galaxies: I. Dependence on Environment and Scale
• Low-J CO Line Ratios From Single Dish CO Mapping Surveys and PHANGS-ALMA
• Molecular depletion times and the CO-to-H2 conversion factor in metal-poor galaxies
• The SAMI Galaxy Survey: Exploring the gas-phase Mass-Metallicity Relation
• Uncovering the Origins of Spiral Structure by Measuring Radial Variation in Pattern Speeds
• The PHANGS-MUSE Nebula Catalogue
• Modeling Dust and Starlight in Galaxies Observed by Spitzer and Herschel: The KINGFISH Sample
• CI and CO in nearby galaxy centers: the bright galaxies NGC1068 (M77), NGC2146, NGC3079, NGC4826 (M64), and NGC7469
• The Polycyclic Aromatic Hydrocarbon Mass Fraction on a 10 pc scale in the Magellanic Clouds
• Remodeling the evolution of grain size distribution in galaxies
• PHANGS-JWST First Results: Destruction of the PAH molecules in HII regions probed by JWST and MUSE
• CO Multi-line Imaging of Nearby Galaxies (COMING) IV. Overview of the Project
• Molecular gas in spiral galaxies: a new warm phase at large galactocentric distances?
• Kinematics of the Atomic ISM in M33 on 80 pc scales
• CI and CO in nearby galaxy centers. The star-burst galaxies NGC 278, NGC 660, NGC 3628, NGC 4631, and NGC 4666
• Central molecular zones in galaxies: 12CO-to-13CO ratios, carbon budget, and X factors
• Molecular Gas Properties and CO-to-H2 Conversion Factors in the Central Kiloparsec of NGC 3351
• The Physical Drivers and Observational Tracers of CO-to-H2 Conversion Factor Variations in Nearby Barred Galaxy Centers
• Molecular gas and dust properties of galaxies from the Great Observatories All-sky LIRG Survey
• PHANGS-JWST First Results: Variations in PAH Fraction as a Function of ISM Phase and Metallicity
• Metals and dust content across the galaxies M101 and NGC 628
• Self-consistent modelling of aromatic dust species and extinction curves in galaxy evolution
• HI, CO, and Dust in the Perseus Cloud
• Polycyclic aromatic hydrocarbons in spatially resolved extragalactic star forming complexes
• Bar effect on gas-phase abundance gradients. I. Data sample and chemical abundances
• Calibration of hybrid resolved star formation rate recipes based on PHANGS-MUSE H$\alpha$ and H$\beta$ maps
• A new census of dust and polycyclic aromatic hydrocarbons at z=0.7-2 with JWST MIRI
• Shiva: the dust destruction model
• Resolving the Dust-to-Metals Ratio and CO-to-H${}_2$ Conversion Factor in the Nearby Universe
• Populating H${}_2$ and CO in galaxy simulation with dust evolution
• CO-to-H${}_2$ Conversion and Spectral Column Density in Molecular Clouds: The Vriability of $X_{\mathrm{CO}}$ Factor
• The Carbon-to-H${}_2$, CO-to-H${}_2$ Conversion Factors and Carbon Abundance on Kiloparsec Scales in Nearby Galaxies
• Benchmarking Dust Emission Models in M101
• Optical and infrared emission of H II complexes as a clue to the PAH life cycle
• Wide-field CO isotopologue emission and the CO-to-H${}_2$ factor across the nearby spiral galaxy M101
• Gas and Dust Properties in the Chamaeleon Molecular Cloud Complex based on the Optically Thick HI
• Effects of dust evolution on the abundances of CO and H${}_2$
• Spectral energy distributions of dust and PAHs based on the evolution of grain size distribution in galaxies
• Evolution of grain size distribution with enhanced abundance of small carbonaceous grains in galactic environments
• Observational signatures of the dust size evolution in isolated galaxy simulations
• Effects of dust grain size distribution on the abundances of CO and H${}_2$ in galaxy evolution
• The Resolved Behavior of Dust Mass, Polycyclic Aromatic Hydrocarbon Fraction, and Radiation Field in ~ 800 Nearby Galaxies

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