Oxygen isotopes reveal low-mass star dominance in the Small Magellanic Cloud
Abstract
Oxygen isotope abundances and their ratios are fingerprints of stellar evolution and therefore provide a powerful tool in tracing the enrichment history of galaxies. However, their behavior in low-metallicity dwarf galaxies remains largely unexplored. The Small Magellanic Cloud (SMC), a nearby analog of young high-redshift galaxies, offers an ideal laboratory to investigate this regime. Using the Atacama Compact Array, we observed the J=2 1 transitions of 12CO, 13CO, C18O, and C17O from the massive star-forming region LIRS~36 (aka N12A), achieving the first detection of C17O in the SMC. This detection enables the first direct measurement of the 18O/17O abundance ratio of 0.870.26 in this galaxy, substantially lower than all values in the literature, including molecular clouds in the Milky Way and other galaxies. Such a low ratio of 18O/17O, together with a high 13CO/C18O ratio, indicates chemical enrichment dominated by low-mass stars, consistent with the observed paucity of high-mass stars in the SMC. We suggest that the SMC is governed by a top-light integrated galaxy-wide initial mass function, predicted by the SMC's persistently low star-formation activities.
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