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We analysed 385 galactic spectra from the Sloan Digital Sky Survey DataRelease 7 (SDSS-DR7) that belong to the catalog of isolated pairs of galaxiesby Karachentsev. The spectra corresponds to physical pairs of galaxies asdefined by V $\leq$ 1200 Km/s and a pair separation $\leq$ 100 kpc. We searchfor the incidence of nuclear activity, both thermal (star-forming) andnon-thermal -Active Galactic Nuclei (AGN). After a careful extraction of thenuclear spectra, we use diagnostic diagrams and find that the incidence of AGNactivity is 48 \% in the paired galaxies with emission lines and 40\% for thetotal sample (as compared to $\sim$ 43 \% and 41\% respectively in a sample ofisolated galaxies). These results remain after dissecting the effects ofmorphological type and galactic stellar mass (with only a small, nonsignificant, enhancement of the AGN fraction in pairs of objects). Theseresults suggest that weak interactions are not necessary or sufficient totrigger low-luminosity AGN. Since the fraction of AGN is predominant in earlytype spiral galaxies, we conclude that the role of a bulge, and a large gasreservoir are both essential for the triggering of nuclear activity. The moststriking result is that type 1 galaxies are almost absent from the AGN sample.This result is in conflict with the Unified Model, and suggests that highaccretion rates are essential to form the Broad Line Region in active galaxies.

Induced nuclear activity in galaxy pairs with different morphologies (E+E), (E+S) and (S+S)