  Recent observational and theoretical studies have suggested that supermassive
black holes (SMBHs) grow mostly through non-merger (`secular') processes. Since
galaxy mergers lead to dynamical bulge growth, the only way to observationally
isolate non-merger growth is to study galaxies with low bulge-to-total mass
ratio (e.g. B/T < 10%). However, bulge growth can also occur due to secular
processes, such as disk instabilities, making disk-dominated selections a
somewhat incomplete way to select merger-free systems. Here we use the
Horizon-AGN simulation to select simulated galaxies which have not undergone a
merger since z = 2, regardless of bulge mass, and investigate their location on
typical black hole-galaxy scaling relations in comparison to galaxies with
merger dominated histories. While the existence of these correlations has long
been interpreted as co-evolution of galaxies and their SMBHs driven by galaxy
mergers, we show here that they persist even in the absence of mergers. We find
that the correlations between SMBH mass and both total mass and stellar
velocity dispersion are independent of B/T ratio for both merger-free and
merger-dominated galaxies. In addition, the bulge mass and SMBH mass
correlation is still apparent for merger-free galaxies, the intercept for which
is dependent on B/T. Galaxy mergers reduce the scatter around the scaling
relations, with merger-free systems showing broader scatter. We show that for
merger-free galaxies, the co-evolution is dominated by radio-mode feedback, and
suggest that the long periods of time between galaxy mergers make an important
contribution to the co-evolution between galaxies and SMBHs in all galaxies.
