Star formation timescale in the circumnuclear starburst ring of barred galaxy NGC 7552

Abstract

We present the multiple line observations carried out with interferometry. We observed the circumnuclear region of the barred galaxy NGC 7552 in molecular lines tracing diffuse molecular gas ( 12CO J 2 - 1; observed by SMA) and relatively dense molecular gas (HCN J 1 - 0; observed by ATCA). We also reprocessed a published HI image which covers the entire galaxy to gain an analytical image with higher resolution. The displacement between HCN (J 1 - 0) and radio knots (3 cm continuum; ATCA archive data) is clearly seen in the circumnuclear starburst ring of NGC 7552. The propagation time derived from 12CO J 2 - 1 and HI based rotation curve between the HCN (J 1 - 0) and radio knots implies the timescale between the formation and death of massive stars. The timescale of NGC 7552 is about an order of magnitude shorter than 5 - 10 Myr timescale for OB stars to become supernovae. It is possible that star formation in the ring is top heavy, resulting in a shorter timescale.