Chemistry and Physics of a Low-metallicity Hot Core in the Large Magellanic Cloud

Abstract

We here present the results of 0.1 pc scale observations in 250 and 350 GHz toward a newly-discovered hot molecular core in a nearby low-metallicity galaxy, the Large Magellanic Cloud (LMC), with the Atacama Large Millimeter/submillimeter Array. A variety of C/N/O/Si/S-bearing molecules are detected toward the high-mass young stellar object, ST16. A rotating protostellar envelope is for the first time detected outside our Galaxy by SO 2 and 34 SO lines. An outflow cavity is traced by CCH and CN. The isotope abundance of sulfur in the source is estimated to be 32 S/ 34 S = 17 and 32 S/ 33 S = 53 based on SO, SO 2 , and CS isotopologues, suggesting that both 34 S and 33 S are overabundant in the LMC. Rotation diagram analyses show that the source is associated with hot gas (>100 K) traced by high-excitation lines of CH 3 OH and SO 2 , as well as warm gas (∼50 K) traced by CH 3 OH, SO 2 , 34 SO, OCS, and CH 3 CN lines. A comparison of molecular abundances between LMC and Galactic hot cores suggests that organic molecules (e.g., CH 3 OH, a classical hot core tracer) show a large abundance variation in low metallicity, where the present source is classified into an organic-poor hot core. Our astrochemical simulations suggest that different grain temperatures during the initial ice-forming stage would contribute to the chemical differentiation. In contrast, SO 2 shows similar abundances within all of the known LMC hot cores, and the typical abundance roughly scales with the LMC’s metallicity. Nitrogen-bearing molecules are generally less abundant in the LMC hot cores, except for NO. The present results suggest that chemical compositions of hot cores do not always simply scale with the metallicity.