Digging into the Chemical Complexity in the Outer Galaxy: A Hot Molecular Core in Sh 2-283

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Abstract The outer Galaxy (Galactocentric distance ≳13.5 kpc) serves as an excellent laboratory for investigating the chemical complexity in low-metallicity environments. Here we present the chemical analyses for the outer Galactic hot core Sh 2-283-1a SMM1 ( D GC = 15.7 kpc and Z ∼ 0.3 Z ⊙ ), recently detected by T. Ikeda et al. using the Atacama Large Millimeter/submillimeter Array. Toward this source, a variety of molecular species, including complex organic molecules (COMs; CH 3 OH, 13 CH 3 OH, CH 2 DOH, and CH 3 OCH 3 ), are detected. The molecular abundances relative to CH 3 OH are similar to those of another outer Galactic hot core, demonstrating that chemically rich hot cores exist in different regions of the outer Galaxy. We also compared molecular abundances among hot cores in the inner Galaxy, outer Galaxy, and Magellanic Clouds. This comparison revealed that the metallicity-corrected N (SO 2 )/ N (H 2 ) ratios of outer Galactic hot cores are significantly lower than those of the inner Galactic ones, while their N (CH 3 OH)/ N (H 2 ) ratios are similar. The Magellanic hot cores show different trends despite having metallicities similar to those of the outer Galaxy, indicating that the chemical complexity of hot cores is governed by environmental conditions (e.g., cosmic-ray intensity and dust temperature) rather than simple metallicity scaling. These environmental differences would also affect the production efficiency of COMs derived from CH 3 OH, as the N (CH 3 OCH 3 )/ N (CH 3 OH) and N (C 2 H 5 OH)/ N (CH 3 OH) ratios in the outer Galactic sources are moderately lower than those of inner Galactic sources. The N (CH 2 DOH)/ N (CH 3 OH) ratio of Sh 2-283-1a SMM1 is 1.5 − 1.2 + 3.9 %, comparable to that of inner Galactic high-mass sources.

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