Journal
ASTROPHYSICAL JOURNAL
Volume 879, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.3847/1538-4357/ab2246
Keywords
galaxies: ISM; galaxies: starburst; ISM: abundances; stars: luminosity function, mass function; submillimeter: galaxies
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Funding
- Canada Council for the Arts through a Killam Research Fellowship
- Natural Sciences and Engineering Research Council of Canada
- Canada Research Chairs program
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We present high-resolution ALMA observations of the (CO)-O-18, (CO)-C-13, and (CO)-C-12 J = 1-0 isotopologues in three nearby ultraluminous infrared galaxies (ULIRGS; Arp 220, IRAS 13120-5453, and IRAS 17208-0014) and one nearby post-merger galaxy (NGC 2623). In all four systems, we measure high (CO)-C-12/(CO)-O-18 and (CO)-C-12/(CO)-C-13 integrated line ratios while the (CO)-C-13/(CO)-O-18 ratio is observed to be extremely low in comparison to typical star-forming disks, supporting previous work. We investigate whether these unusual line ratios are due to dynamical effects, astrochemistry within the gas, or nucleosynthesis in stars. Assuming both lines are optically thin, low (CO)-C-13/(CO)-O-18 values suggest that (CO)-O-18 is more abundant than (CO)-C-13 in the interstellar medium of these systems. A plausible explanation is that local ULIRGs and their progeny have an excess in massive star formation; in other words, they are producing a top-heavy stellar initial mass function.
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