NOBEYAMA MILLIMETER ARRAY OBSERVATIONS OF LUMINOUS INFRARED GALAXIES

We present, the results of systematic millimeter interferometric observations of luminous infrared galaxies (LIRGs), using the Nobeyama Millimeter Array. We observed HCN (J = 1-0) and HCO(+) (J = 1-0) emission lines simultaneously, and derived their brightness-temperature ratios, to investigate whether the observed ratios are similar to those found hi AGN-dominated nuclei or starburst galaxies. LIRGs with (without) luminous buried AGN signatures in our infrared spectra tend to slow high (low) HCN (J = 1-0) to HCO(+) (J = 1.0) brightness-temperature ratios as seen in galaxy nuclei dominated by AGNs (starbursts). The high ratios in buried AGN candidates could be explained by the enhanced HCN abundance, and/or infrared radiative, pumping. of the HCN molecule. ill the close vicinity of all AGN.