It is widely accepted that quasars (luminous active galactic nuclei (AGNs)) are triggered by major mergers among galaxies. On the other hand, as for Seyfert galaxies (less-luminous AGNs), their triggering mechanisms are still in debate. Since most Seyferts in the nearby Universe show ordinary or undisturbed structures (i.e., ordinary spiral galaxies), internal mechanisms, such as the secular evolution, the bar-driven inflow, and so on, have been thought to work in them other than galaxy interactions and mergers. Indeed, there is little evidence for major mergers in Seyferts. However, since any galaxies tend to have their satellite galaxies, minor mergers with them can be one possible mechanism for triggering nuclear activity in Seyferts. Recently, we have found the firm evidence for a past minor merger in the archetypical Seyfert galaxy NGC 1068 that has been considered as an undisturbed, symmetric spiral galaxy, suggesting the importance of the minor merger triggering. In order to improve our understanding of the triggering mechanism in Seyferts, we propose to make deep imaging of a sample of seven nearby Seyfert galaxies with HSC down to the surface brightness of ∼29 mag/arcsec2 in r2-band.
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