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 aswell as CO in all the galaxies. The I(HCN)/I(CO) ratios were 0.025+-0.006 and0.066+-0.005 in NGC 3593 and NGC 4293, respectively, which are comparable tothe late-type spiral galaxies. The average of the I(HCN)/I(CO) ratios at thecenter of 12 nearby spiral galaxies including late-type was 0.055+-0.028. Theline 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 COpeaks were near the systemic velocity. These results suggest that the fractionof the dense molecular gas is high around the center in these galaxies.Comment: 8 pages, 2 figures, to be published in PASJ (Publications of the Astronomical Society of Japan) Vol.54, No.