The thermal state of molecular clouds in the Galactic center: evidence for non-photon-driven heating

We have used the Atacama Pathfinder Experiment (APEX) 12 m telescope at 218 GHz to observe molecular clouds simultaneously in the J_KaKc = 3₀₃→2₀₂, 3₂₂→2₂₁, and 3₂₁→2₂₀ transitions of para-H₂CO to determine kinetic temperatures of the dense gas in the central molecular zone of the Galaxy. Gas kinetic temperatures for individual molecular clouds range from 55 to 125 K or even higher. The molecular clouds at high temperatures may be heated by turbulent dissipation and/or cosmic-rays.