The Detection of Hot Molecular Cores in the Small Magellanic Cloud

Abstract

We report the first detection of hot molecular cores in the Small Magellanic Cloud (SMC), a nearby dwarf galaxy with 0.2 solar metallicity. We observed two high-mass young stellar objects in the SMC with the Atacama Large Millimeter/submillimeter Array and detected emission lines of CO, HCO ^+ , H ^13 CO ^+ , SiO, H _2 CO, CH _3 OH, SO, and SO _2 . Compact hot-core regions are traced by SO _2 , whose spatial extent is about 0.1 pc, and the gas temperature is higher than 100 K based on the rotation diagram analysis. In contrast, CH _3 OH, a classical hot-core tracer, is dominated by extended (∼0.2–0.3 pc) components in both sources, and the gas temperature is estimated to be ${39}_{-6}^{+8}$ K for one source. Protostellar outflows are also detected from both sources as high-velocity components of CO. The metallicity-scaled abundances of SO _2 in hot cores are comparable among the SMC, Large Magellanic Cloud (LMC), and Galactic sources, suggesting that the chemical reactions leading to SO _2 formation would be regulated by elemental abundances. On the other hand, CH _3 OH shows a large abundance variation within SMC and LMC hot cores. The diversity in the initial condition of star formation (e.g., degree of shielding, local radiation field strength) may lead to the large abundance variation of organic molecules in hot cores. This work, in conjunction with previous hot-core studies in the LMC and outer/inner Galaxy, suggests that the formation of a hot core would be a common phenomenon during high-mass star formation across the metallicity range of 0.2–1 Z _⊙ . High-excitation SO _2 lines will be a useful hot-core tracer in the low-metallicity environments of the SMC and LMC.

Keywords

• Astrochemistry
• Interstellar molecules
• Protostars
• Magellanic Clouds
• Complex organic molecules
• Radio astronomy