Dense Molecular Gas in Lenticular Galaxies

We made CO and HCN simultaneous observations of lenticular galaxies (NGC 404, NGC 3593, and NGC 4293) and detected HCN emission in NGC 3593 and NGC 4293 as well as CO in all the galaxies. The IHCN/ICO ratios were 0.025 ±0.006 and 0.066 ±0.005 in NGC 3593 and NGC 4293, respectively, which are comparable to that of late-type spiral galaxies. The average of the IHCN/ICO ratios at the center of 12 nearby spiral galaxies including the late type was 0.055 ±0.028. The line profiles of CO and HCN emission showed different shape in both galaxies. The HCN peaks were not at the systemic velocity of these galaxies, while the CO peaks were near the systemic velocity. These results suggest that the fraction of dense molecular gas is high around the center of these galaxies.