Kinematic analysis of the massive star-forming region G328.2551-0.5321 via alma molecular line observations

Abstract

This study reports on high-angular-resolution observations of the massive star-forming region G328.2551−0.5321 obtained with the Atacama Large Millimeter/submillimeter Array at a wavelength of 0.89 mm. The innermost core structure is investigated by targeting high-excitation transitions of methanol, sulfur dioxide, and its sulfur-34 isotopologue. Analysis of the molecular emission reveals a compact and dense methanol component located at the continuum peak, which is surrounded by more extended emission from sulfur-bearing molecules. Kinematic analysis demonstrates a coherent velocity gradient along the major axis of the system. Position–velocity diagrams exhibit a characteristic butterfly morphology, which is consistent with the presence of a Keplerian rotation. Numerical model fitting provides dynamical mass estimates of approximately twenty solar masses for the central object, confirming the existence of a massive, rotating disk-like structure. Rotational diagram analysis of methanol transitions yields a rotational temperature of 187.9 ± 23.7 Kelvin and a total column density of 4.27 × 10¹⁶ cm⁻², indicating the presence of a hot molecular core. These findings suggest that a high-mass protostar is actively accreting within a compact disk-envelope system embedded in a hot core environment. The results contribute to the understanding of the physical conditions and gas dynamics in the early stages of massive star formation.