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 \sim 10 ^ { \prime \prime } 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 , R _ { HCN / CO } , 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 \times 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 ) .