The FeII problem in NLS1s

For more than twenty years, strong Fe II emission lines have been observed in Active Galactic Nuclei and in particular in Narrow Line Seyfert 1 galaxi es. A quick overview of the observations and of the models proposed to inte rpret the Fe Il spectrum is given. The influence of atomic data and of phys ical parameters are discussed, and it is shown that the strengths of the Fe II lines cannot be explained in the framework of photoionization models. A non-radiative heating, for instance due to shocks, with an overabundance o f iron, can help to solve the problem. A comparison with other objects emit ting intense Fe II lines favors also the presence of strong outflows and sh ocks. We suggest some issues in the context of AGN evolution. (C) 2000 Else vier Science B.V. All rights reserved.