Abstract

Contributed Talk - Splinter GalaxyEvol

Thursday, 12 September 2024, 17:39   (S21)

13CO(1-0)/C18O(1-0) Ratio Variations Across the Whirlpool Galaxy

Ina Galić, Frank Bigiel, Eva Schinnerer, Mallory Thorp, Hao He, Dario Colombo, Antonio Usero, María J. Jiménez-Donaire
AIfA, MPIfR, MPIA, OAN

In extragalactic studies, CO and its isotopologues are crucial tracers of bulk molecular gas, which serves as a reservoir for the formation of new stars. While these isotopologues have been extensively studied at high resolution within our Galaxy, high-resolution observations beyond our Galaxy have traditionally been limited to galaxy centers, starburst galaxies, or (ultra-)luminous infrared galaxies ((U)LIRGs). However, advancements in interferometry are now enabling increasingly detailed and spatially comprehensive surveys of normal star-forming galaxies as well. One such survey is SWAN (Surveying the Whirlpool at Arcseconds with NOEMA), in which our team observed the inner 5 x 7 kpc of the nearby, face-on grand design spiral galaxy M51. The survey mapped 13CO(1-0), C18O(1-0), and multiple dense gas emission lines at an unprecedented resolution of ~125 pc for a galaxy of this type. Using SWAN, we present an analysis of how the spatial distribution of 13CO(1-0) and C18O(1-0) line emission in M51 is influenced by changes in opacity and molecular abundance, which reflect the underlying physical and chemical conditions of the gas. To achieve this, we investigate how the integrated intensity ratio of 13CO(1-0) to C18O(1-0) varies with galactocentric radius and star formation rate surface density. Our analysis encompasses a wide range of environments within M51, including the nuclear bar, molecular ring, northern and southern spiral arms, and interarm regions. We find a moderate positive correlation with galactocentric radius and a moderate negative correlation with star formation rate surface density. These findings are consistent with previous studies conducted at kiloparsec scales in nearby star-forming galaxies, implying that the physical and chemical processes governing the ratio may operate similarly at both scales. We propose that selective nucleosynthesis, a mechanism related to age and mass of present stellar populations, is the primary driver of the observed variations in the line ratio. Changes in the opacity of 13CO also play a contributing, but lesser, role. Additionally, the observed correlations vary within different galactic environments, implying localized processes and conditions within a galaxy either enhance or suppress these trends.