Presentation #113.03 in the session Spiral Galaxies.
Optically thin 13CO and C18O allow us to investigate the physical causes for abundance variations across the spiral disks of galaxies. Correlation between the 13CO/C18O ratio and ΣSFR can indicate either chemical fractionation or selective enrichment by stellar nucleosynthesis. We use data taken by the Green Bank Telescope (GBT) and Argus to measure the 13CO/C18O ratio and a combination of infrared (IR) and far ultraviolet to trace star formation rate surface density (ΣSFR) in nearby spiral galaxies. This project uses three different region selection methods to find the relation: the central 15” of each galaxy, 0.16×r25 of each galaxy, and radial profiles starting from the center and increasing by 15” galactocentric radius for each region. After plotting the 13CO/C18O ratio as a function of ΣSFR for all region selection methods, we found that the 13CO/C18O ratio increased with increasing ΣSFR with a slope of 0.07±0.03 for central regions, decreased with increasing ΣSFR with a slope of -0.7±1.0 for whole galaxy regions, and consistently decreased for the radial profiles with two galaxies (NGC 3631 and NGC 5055) as outliers. We see evidence for both chemical fractionation and selective enrichment, indicating that no one mechanism appears to dominate in all scenarios.