The ALMA-ATOMS Survey: Methanol Emission in a Large Sample of Hot Molecular Cores

Abstract

Abstract Methanol (CH 3 OH) is a key complex organic molecule (COM) in the interstellar medium, widely used as a tracer of dense gas and hot molecular cores (HMCs). Using high-resolution Atacama Large Millimeter/submillimeter Array observations from the ATOMS survey, we investigate the excitation and abundance of methanol nuclear spin isomers and their relationship to chemical complexity in massive star-forming cores. We identify 20 methanol transitions, including A- and E-type lines in the v = 0 state and E-type lines in the v t = 1 state, and detect 94 HMC candidates. Rotational temperature analysis under the LTE assumption yields average values of 194 ± 33 K for CH 3 OH-E v t = 1, 178 ± 33 K for CH 3 OH-A v = 0, and 75 ± 21 K for CH 3 OH-E v = 0. Emission from COMs other than methanol is detected in 87 of the 94 cores, with the CH 3 OH-E v t = 1 line intensity showing a strong correlation with the channel detection ratio (CDR). These results demonstrate that CH 3 OH-E v t = 1 lines are reliable tracers of HMCs and chemical complexity, and that the CDR provides a robust indicator of molecular richness. The temperature difference between A- and E-type methanol transitions is driven by anomalously strong J(2,J-2)−J(-1,J-1) lines, highlighting the importance of analyzing methanol symmetry types separately.