Vibrationally excited HC3N in NGC 4418

摘要: Aims. We investigate the molecular gas properties of deeply obscured luminous infrared galaxy NGC 4418. address excitation complex molecule HC3N to determine whether its unusually emission is related nature buried nuclear source. Methods. use IRAM 30 m and JCMT observations rotational vibrational lines model by means diagrams. Results. report first confirmed extragalactic detection HC3N. detect 6 different transitions ranging from J = 10–9 30–29 in ground state obtain a tentative 38–37 line. also 7 vibrationally excited states v6 v7, with angular momenta 28–27. The energies upper observed range 20 850 K. In optically thin regime, we find that can be fitted for two temperatures, K 260 K, while levels temperature 90 500 inner 300 pc 4418, estimate high abundance, order 10-7. Conclusions. responds strongly intense radiation field presence warm, dense dust at center line result both abundances excitation. emitting are similar those found hot cores Sgr B2, which implies nucleus (<300 pc) 4418 reminiscent core. potential compact, component (T K) discussed.