The main process triggering AGN activity could be a function of redshift and/or halo mass. 2006 Hopkins & Hernquist 2006, 2009), and probably also by the interaction with very small satellites (total mass ratio of about 1:100), as recently suggested by Ramón-Fox & Aceves (2014). Low luminosity AGNs could also be triggered in non-merger scenarios (e.g., Milosavljević et al.
2012) have found that the more luminous AGNs show recent merger features, while such features are not commonly seen in the less luminous AGNs, which appear to be driven by another process. Visual inspections of host galaxies of AGNs ( Treister et al.
Major galaxy mergers are very efficient in moving gas to galaxy centers due to the generation of large torques. Mergers and strong interactions can induce substantial gravitational torques on the gas content of a galaxy, depriving it of its angular momentum, and leading to gas inflows and the buildup of huge reservoirs of gas at its center (e.g., Hernquist 1989 Barnes & Hernquist 1991, 1996 Mihos & Hernquist 1996 Springel et al. 2011), collisions with molecular clouds ( Hopkins & Hernquist 2006), stellar winds from evolved stars ( Ciotti & Ostriker 2007), and the transportation of gas to galactic centers by supernova explosions ( Chen et al. 2008), bar-driven inflows (e.g., Jogee 2006), disk instabilities ( Bournaud et al. This activity is related to the accretion of material onto the central engine triggered by, for example: the merger of gas-rich galaxies (e.g., Silk & Rees 1998 Springel et al. 2000 Merritt & Ferrarese 2001 Tremaine et al. The observed correlation between the mass of the central BH and the velocity dispersion (σ) of the bulge of the host galaxy suggest a strong connection between galaxy evolution and BH activity (e.g., Gebhardt et al. 2009 Alexander & Hickox 2012 Beckmann & Shrader 2012). Studies of AGN host galaxies are fundamental to understand the physical mechanisms that trigger AGN activity and that govern the fuelling rate of the central black hole (e.g., Gilmour et al.
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