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 find a striking enhancement of the HCN emission toward the active nucleus of NGC 1097; a large fraction of the CO emission comes from the 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 in brightness temperature scale is about 0.11 in the aperture of the 45 m telescope beams (r < 510 pc for CO and r < 640 pc for HCN), but it reaches 0.34 in the smaller aperture (within the central r < 350 x 150 pc region). 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).