High-mass star-forming regions are rich in complex organic molecules (COMs), which are carbon-bearing species with at least six atoms. Their formation pathways remain debated. The ALMA evolutionary study of high-mass protocluster formation in the GALaxy (ALMAGAL) survey provides a unique opportunity to probe this chemical complexity in a large statistical significant sample of high-mass star-forming regions. We present a detailed molecular line analysis of one of the most chemically rich cores in the ALMAGAL sample, the high-mass core 9 in the AG318. 9477-00. 1960 clump (AG318-c9), located at a heliocentric distance of ∼ 10. 4, ̊m kpc. This source was selected because it combines an exceptionally high line density with a relatively simple kinematic structure, making it an optimal template for chemical analysis in the survey. We further assessed whether the emission of selected COMs, that is, ethylene glycol (̊m (CH₂OH) ₂; EG), glycolaldehyde (̊m CH₂ (OH) CHO; GA), and methyl formate (̊m CH₃OCHO; MF), can be used to trace the innermost regions of hot molecular cores (HMCs). We analysed ALMA Band 6 observations (∼ 217-221, GHz). Spectral line identification and local thermodynamic equilibrium modelling were performed using the software called MAdrid Data CUBe Analysis (MADCUBA). We derived the physical parameters, including the column density (N), excitation temperature (T_̊m ex), velocity, line width, and molecular abundances relative to ̊m H₂, for all detected species. The chemical inventory of AG318-c9 was compared with that of the HMC ̊m G31. 41+0. 31 (G31). In addition, we performed a pixel-by-pixel analysis of EG, GA, and MF to generate spatially resolved N and T_̊m ex maps and corresponding radial profiles. We report the detection of 65 molecular species, including 31 main species and 34 isotopologues and vibrationally excited species. Of these, 44 are O-bearing species, 28 are N-bearing, 8 are S-bearing, and 2 are Si-bearing. While AG318-c9 exhibits lower abundances than G31 overall, it shows detections of species that have not yet been reported in G31, such as ethyl formate (̊m C₂H₅OCHO). Moreover, 12 species depart from the general trend, displaying relative overabundances in AG318-c9. The comparison also reveals a chemical differentiation between O- and N- bearing COMs, with O-bearing species systematically more abundant in G31. Regarding EG, GA, and MF, the latter is the most abundant (X ∼ 3), followed by EG (X∼ 7) and GA (X ∼ 2). The N and T_̊m ex maps suggest that MF is the most spatially extended species, whereas EG and GA are more compact and confined to the innermost hot region. 10^ -8 10^ -9 10^ -9 AG318-c9 reveals a rich chemical inventory characteristic of an HMC. The chemical comparison with G31 suggests that AG318-c9 is a less evolved hot core dominated by the recent sublimation of ice mantles, in contrast to the higher abundances observed in the possible more evolved G31. MF emerges as an excellent tracer of the gas temperature in HMCs owing to its wide spatial extent and wide dynamic range of the excitation temperature. In contrast, EG and GA are more compact and preferentially trace the innermost high-density regions of the core, suggesting a high sublimation temperature threshold and supporting a shared grain-surface formation pathway. While EG and MF seem to be partly limited by sensitivity, GA reflects an intrinsically central distribution.
Allande et al. (Tue,) studied this question.
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