Full-disc ${}^{13}$CO(1-0) mapping across nearby galaxies of the EMPIRE survey and the CO-to-H${}_2$ conversion factor

Abstract

Carbon monoxide (CO) provides crucial information about the molecular gas properties of galaxies. While ${}^{12}$CO has been targeted extensively, isotopologues such as ${}^{13}$CO have the advantage of being less optically thick and observations have recently become accessible across full galaxy discs. We present a comprehensive new dataset of ${}^{13}$CO(1-0) observations with the IRAM 30-m telescope of the full discs of 9 nearby spiral galaxies from the EMPIRE survey at a spatial resolution of $\sim$1.5kpc. ${}^{13}$CO(1-0) is mapped out to $0.7-1r_{25}$ and detected at high signal-to-noise throughout our maps. We analyse the ${}^{12}$CO(1-0)-to-${}^{13}$CO(1-0) ratio ($\Re$) as a function of galactocentric radius and other parameters such as the ${}^{12}$CO(2-1)-to-${}^{12}$CO(1-0) intensity ratio, the 70-to-160$\mu$m flux density ratio, the star-formation rate surface density, the star-formation efficiency, and the CO-to-H${}_2$ conversion factor. We find that $\Re$ varies by a factor of 2 at most within and amongst galaxies, with a median value of 11 and larger variations in the galaxy centres than in the discs. We argue that optical depth effects, most likely due to changes in the mixture of diffuse/dense gas, are favored explanations for the observed $\Re$ variations, while abundance changes may also be at play. We calculate a spatially-resolved ${}^{13}$CO(1-0)-to-H${}_2$ conversion factor and find an average value of $1.0\times 10^{21}$ cm${}^{-2}$ (K.km/s)${}^{-1}$ over our sample with a standard deviation of a factor of 2. We find that ${}^{13}$CO(1-0) does not appear to be a good predictor of the bulk molecular gas mass in normal galaxy discs due to the presence of a large diffuse phase, but it may be a better tracer of the mass than ${}^{12}$CO(1-0) in the galaxy centres where the fraction of dense gas is larger.

accepted for publication in MNRAS

References in corpus (26)

• The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers
• CO Isotopologues in the Perseus Molecular Cloud Complex: the X-Factor and Regional Variations
• Ultraviolet Survey of CO and H_2 in Diffuse Molecular Clouds: The Reflection of Two Photochemistry Regimes in Abundance Relationships
• The impact of interactions, bars, bulges, and AGN on star formation efficiency in local massive galaxies
• HI-to-H2 Transitions and H I Column Densities in Galaxy Star-Forming Regions
• The evolution of CNO isotopes: a new window on cosmic star-formation history and the stellar IMF in the age of ALMA
• Cloud Scale ISM Structure and Star Formation in M51
• On carbon and oxygen isotope ratios in starburst galaxies: New data from NGC253 and Mrk231 and their implications
• Millimeter-Wave Line Ratios and Sub-beam Volume Density Distributions
• Abundances and Isotope Ratios in the Magellanic Clouds: The Star Forming Environment of N113
• Formation, fractionation and excitation of carbon monoxide in diffuse clouds
• CI and CO in nearby galaxy centers: the bright galaxies NGC1068 (M77), NGC2146, NGC3079, NGC4826 (M64), and NGC7469
• A Survey of the Molecular ISM Properties of Nearby Galaxies using the Herschel FTS
• Molecular line mapping of the giant molecular cloud associated with RCW 106 - II. Column density and dynamical state of the clumps
• Optical Depth Estimates and Effective Critical Densities of Dense Gas Tracers in the Inner Parts of Nearby Galaxy Discs
• A revised planetary nebula luminosity function distance to NGC 628 using MUSE
• Using CO line ratios to trace the physical properties of molecular clouds
• ${}^{13}$CO/C${}^{18}$O Gradients Across the Disks of Nearby Spiral Galaxies
• Nuclear Bar Catalyzed Star Formation: 13^CO, C18^O and Molecular Gas Properties in the Nucleus of Maffei 2
• Systematic variation of the 12CO/13CO ratio as a function of star-formation rate surface density
• Interpreting the sub-linear Kennicutt-Schmidt relationship: The case for diffuse molecular gas
• The cooling of atomic and molecular gas in DR21
• CO Multi-line Imaging of Nearby Galaxies (COMING): I. Physical properties of molecular gas in the barred spiral galaxy NGC 2903
• Spatially Resolved Chemistry in Nearby Galaxies III. Dense Molecular Gas in the Inner Disk of the LIRG IRAS 04296+2923
• CARMA Survey toward Infrared-bright Nearby Galaxies (STING). IV. Spatially Resolved 13CO in Spiral Galaxies
• CO observations of a sample towards nearby galaxies

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