2009ApJ...694..610M

The chemistry in the central regions of galaxies is expected to be strongly influenced by their nuclear activity. To find the best tracers of nuclear activity is of key importance to understand the processes taking place in the most obscured regions of galactic nuclei. In this work, we present multiline observations of CS, C³⁴S, HNCO, and C¹⁸O in a sample of 11 bright galaxies prototypical for different types of activity. The ³²S/³⁴S isotopic ratio is ∼10, supporting the idea of an isotopical ³⁴S enrichment due to massive star formation in the nuclear regions of galaxies. Although C³²S and C³⁴S do not seem to be significantly affected by the activity type, the HNCO abundance appears highly contrasted among starbursts (SBs). We observed HNCO abundance variations of nearly 2 orders of magnitude. The HNCO molecule is shown to be a good tracer of the amount of molecular material fueling the SB and therefore can be used as a diagnostics of the evolutionary state of a nuclear SB.