Vibrationally Excited HC3N in NGC 4418

Luminous infrared galaxies (LIRGs) emit most of their radiation in the infrared region of the spectrum in the form of dust thermal continuum, with typical luminosities of LIR >1010 L . The central power source responsible for the total energy output is deeply buried in the dusty central regions of these objects and its origin still unclear. Recent studies by Spoon et al. (2007) and Aalto et al. (2007) suggest that some LIRGs might represent early obscured stages of active galaxies, either AGNs or starbursts, and thus play a fundamental role in galaxy formation and evolution.