2022MNRAS.516.1094R

Using high angular resolution ALMA observations (0.02 arcsec ≈ 0.34 pc), we study the thermal structure and kinematics of the proto-super star cluster 13 in the central region of NGC 253 through their continuum and vibrationally excited HC₃N emission from J = 24-23 and J = 26-25 lines arising from vibrational states up to v₄ = 1. We have carried 2D-LTE and non-local radiative transfer modelling of the radial profile of the HC₃N and continuum emission in concentric rings of 0.1 pc width. From the 2D-LTE analysis, we found a Super Hot Core (SHC) of 1.5 pc with very high vibrational temperatures (>500 K), and a jump in the radial velocity (21 km s^–1) in the SE-NW direction. From the non-local models, we derive the HC₃N column density, H₂ density, and dust temperature (T_dust) profiles. Our results show that the thermal structure of the SHC is dominated by the greenhouse effect due to the high dust opacity in the IR, leading to an overestimation of the LTE T_dust and its derived luminosity. The kinematics and T_dust profile of the SHC suggest that star formation was likely triggered by a cloud-cloud collision. We compare proto-SSC 13 to other deeply embedded star-forming regions, and discuss the origin of the $L_\text{IR}/M_{\text{H}_2}$ excess above ∼100 L_⊙ M$_\odot ^{-1}$ observed in (U)LIRGs.