Extreme Optical Fe II Emission in Luminous IRAS Active Galactic Nuclei

We present results of a program of studies and observations of strong optical Fe II emission in luminous and ultraluminous IRAS active galactic nuclei (AGNs). We report here (1) new spectroscopic observations and studies of three known ultraluminous IRAS AGNs with extreme optical Fe II emission; (2) the discovery that PHL 1092 (the most extreme Fe II emitting AGN detected) is a new ultraluminous IRAS AGN; (3) the fact that most, if not all, known AGNs with extreme optical Fe II emission are luminous/ultraluminous IRAS AGNs; (4) the detection of two new AGNs with strongly variable flux in the optical Fe II emission lines. We use these results to test the correlations between the Fe II emission and properties at other wavelengths such as the L_IR_ and the radio emission. The results and the origin of the strong optical Fe II emission are discussed in terms of the model of a composite nature for the nuclear energy source in luminous IRAS galaxies: an AGN embedded in a starburst environment. We find that IR AGNs with extreme Fe II emission belong to a very important group of AGNs (possibly young IR QSO), whose properties give us new insights into the origin of the extreme Fe II emission and into the relation between the starburst and AGN phenomena.