Activity induced by Gravitational Interaction in Galaxy Pairs
  A systematic study of the nuclear emission of a sample of 97 spirals in isolated galaxy pairs with mixed morphology (E+S) shows that: 1) AGN activity is found in 40% of the spiral galaxies in these pairs, 2) Only one out of the 39 AGN found has type 1 (Broad line Component) activity, and 3) AGN tend to have closer companions than star forming galaxies. These results are at odds with a simple Unified Model for Seyferts, where only obscuration/orientation effects are of relevance, and neatly support an evolutionary scenario where interactions trigger nuclear activity, and obscuration/orientation effects may be complementary in a certain evolutionary phase. 
D. Dultzin, J.J. Gonzalez, Y. Krongold, H. Hernandez-Toledo, E.M.   Huerta, I. Cruz-Gonzalez, L. Olguin, P. Marziani, F. Her...