2025A&A...694A.166C

Context. Interstellar molecules are excellent tools for studying the physical and chemical environments of massive star-forming regions. In particular, the vibrationally excited HC₃N (HC₃N*) lines are the key tracers for probing hot cores environments.
Aims. We present the Atacama Large Millimeter/submillimeter Array (ALMA) 3 mm observations of HC₃N* lines in 60 hot cores and investigate how the physical conditions affect the excitation of HC₃N* transitions.
Methods. We used the XCLASS for line identification. Under the assumption of local thermodynamic equilibrium, we derived the rotation temperature and column density of HC₃N* transitions in hot cores. Additionally, we calculated the H₂ column density and number density, along with the abundance of HC₃N* relative to H₂, to enable a comparison of the physical properties of hot cores with different numbers of HC₃N* states.
Results. We have detected HC₃N* lines in 52 hot cores, 29 of which show more than one vibrationally excited state. Hot cores with higher gas temperatures have more detections of these vibrationally excited lines. The excitation of HC₃N* requires dense environments, and its spatial distribution is affected by the presence of UC HII regions. The observed column density of HC₃N* contributes to the number of HC₃N* states in hot-core environments.
Conclusions. After analyzing the various factors influencing HC₃N* excitation in hot cores, we conclude that the excitation of HC₃N* is mainly driven by mid-IR pumping, while collisional excitation is ineffective.