Enhanced HCN (1-0) emission in the type-1 seyfert galaxy NGC 1097

Abstract

The central kpc region of the low-luminosity type-1 Seyfert galaxy NGC 1097 has been observed in the CO (1-0) and HCN (1-0) lines with the Nobeyama Millimeter Array and the NRO 45 m telescope. We have found a striking enhancement of the HCN emission toward the active nucleus of NGC 1097; a large fraction of the CO emission comes from a circumnuclear starburst ring (r ∼ 10″ or 700 pc at D = 14.5 Mpc), whereas the HCN emission is dominated by a strong unresolved peak at the nucleus. The HCN-to-CO integrated intensity ratio on the brightness temperature scale, RHCN/CO, is about 0.11 in the aperture of the 45 m telescope beams (15″ for CO and 19″ for HCN), but reaches 0.34 in the smaller aperture (10″ 4.″4). These CO and HCN properties in NGC 1097 are similar to those in the type-2 Seyfert galaxies NGC 1068 and NGC 5194 (M 51).