A Multiline Study of a High-mass Young Stellar Object in the Small Magellanic Cloud with ALMA: The Detection of Methanol Gas at 0.2 Solar Metallicity

Abstract

We report the results of subparsec-scale submillimeter observations toward an embedded high-mass young stellar object in the Small Magellanic Cloud (SMC) with ALMA. Complementary infrared data obtained with the AKARI satellite and the Gemini South telescope are also presented. The target infrared point source is spatially resolved into two dense molecular cloud cores; one is associated with a high-mass young stellar object (YSO core), while another is not associated with an infrared source (East core). The two cores are dynamically associated but show different chemical characteristics. Emission lines of CS, C 33 S, H 2 CS, SO, SO 2 , CH 3 OH, H 13 CO + , H 13 CN, SiO, and dust continuum are detected from the observed region. Tentative detection of HDS is also reported. The first detection of CH 3 OH in the SMC has a strong impact on our understanding of the formation of complex organic molecules in metal-poor environments. The gas temperature is estimated to be ∼10 K based on the rotation analysis of CH 3 OH lines. The fractional abundance of CH 3 OH gas in the East core is estimated to be (0.5–1.5) × 10 −8 , which is comparable to or marginally higher than those of similar cold sources in our Galaxy despite a factor of five lower metallicity in the SMC. This work provides observational evidence that an organic molecule like CH 3 OH, which is largely formed on grain surfaces, can be produced even in a significantly lower metallicity environment compared to the solar neighborhood. A possible origin of cold CH 3 OH gas in the observed dense core is discussed.