  We present new broad-band optical images of some merging Seyfert galaxies
that were earlier considered to be non-interacting objects. On our deep images
obtained at the Russian 6-m telescope we have detected elongated tidal
envelopes belonging to satellites debris with a surface R-band brightness about
25-26.5 mag/arcsec^2. These structures are invisible in Sloan Digital Sky
Survey (SDSS) pictures because of their photometric limit. We found that 35 per
cent of the sample of isolated galaxies has undergone merging during the last
0.5-1 Gyr. Our results suggest that statistic studies based on popular imaging
surveys (SDSS or Second Palomar Observatory Sky Survey (POSS-II)) can lead to
underestimation of the fraction of minor mergers among galaxies with active
nuclei (AGN). This fact impacts on statistics and must be taken into
consideration when finding connection between minor/major merging or
interactions and nucleus activity.
