Surveying the Whirlpool at Arcseconds with NOEMA (SWAN): III. ${}^{13}$CO/C${}^{18}$O ratio variations across the M51 galaxy

Abstract

CO isotopologues are common tracers of the bulk molecular gas in extragalactic studies, providing insights into the physical and chemical conditions of the cold molecular gas, a reservoir for star formation. Since star formation occurs within molecular clouds, mapping CO isotopologues at cloud-scale is important to understanding the processes driving star formation. However, achieving this mapping at such scales is challenging and time-intensive. The Surveying the Whirlpool Galaxy at Arcseconds with NOEMA (SWAN) survey addresses this by using the Institut de radioastronomie millimétrique (IRAM) NOrthern Extended Millimeter Array (NOEMA) to map the ${}^{13}$CO(1-0) and C${}^{18}$O(1-0) isotopologues, alongside several dense gas tracers, in the nearby star-forming galaxy M51 at high sensitivity and spatial resolution ($\approx$ 125 pc).We examine the ${}^{13}$CO(1-0) to C${}^{18}$O(1-0) line emission ratio as a function of galactocentric radius and star formation rate surface density to infer how different chemical and physical processes affect this ratio at cloud scales across different galactic environments: nuclear bar, molecular ring, northern and southern spiral arms. In line with previous studies conducted at kiloparsec scales for nearby star-forming galaxies, we find a moderate positive correlation with galactocentric radius and a moderate negative correlation with star formation rate surface density across the field-of-view (FoV), with slight variations depending on the galactic environment. We propose that selective nucleosynthesis and changes in the opacity of the gas are the primary drivers of the observed variations in the ratio.

Accepted for publication in A&A; 8 pages, 4 pages Appendix, 10 figures

References in corpus (23)

• The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers
• The evolution of CNO isotopes: a new window on cosmic star-formation history and the stellar IMF in the age of ALMA
• Galactic interstellar 18O/17O ratios - a radial gradient?
• Full-disc ${}^{13}$CO(1-0) mapping across nearby galaxies of the EMPIRE survey and the CO-to-H${}_2$ conversion factor
• CI and CO in nearby galaxy centers: the bright galaxies NGC1068 (M77), NGC2146, NGC3079, NGC4826 (M64), and NGC7469
• A New Diagnostic to Separate Line Emission from Star Formation, Shocks, and AGN Simultaneously in IFU Data
• Using CO line ratios to trace the physical properties of molecular clouds
• AGN feedback in the nucleus of M51
• ${}^{13}$CO/C${}^{18}$O Gradients Across the Disks of Nearby Spiral Galaxies
• The Physical Drivers and Observational Tracers of CO-to-H2 Conversion Factor Variations in Nearby Barred Galaxy Centers
• WISDOM Project -- X. The morphology of the molecular ISM in galaxy centres and its dependence on galaxy structure
• Are local ULIRGs powered by AGN? The sub-kpc view of the 220 GHz continuum. PUMA II
• Systematic variation of the 12CO/13CO ratio as a function of star-formation rate surface density
• Kinetic temperature of massive star forming molecular clumps measured with formaldehyde
• Extreme CO Isotopologue Line Ratios in ULIRGS: Evidence for a top-heavy IMF
• The ALMOND Survey: Molecular cloud properties and gas density tracers across 25 nearby spiral galaxies with ALMA
• Diverse Molecular Structures Across The Whole Star-Forming Disk of M83: High fidelity Imaging at 40pc Resolution
• A CO isotopologue Line Atlas within the Whirlpool galaxy Survey (CLAWS)
• CO Excitation and its Connection to Star Formation at 200 pc in NGC 1365
• Molecular Gas Kinematics and Line Diagnostics in Early-type Galaxies: NGC4710 and NGC5866
• Spectral Stacking of Radio-Interferometric Data
• Surveying the Whirlpool at Arcseconds with NOEMA (SWAN)- I. Mapping the HCN and N${}_2$H${}^{+}$ 3mm lines
• Surveying the Whirlpool at Arcseconds with NOEMA (SWAN) II: Survey design and observations