  Dwarf galaxies (M*<10^9 Msun) are key drivers of mass assembly in high mass
galaxies, but relatively little is understood about the assembly of dwarf
galaxies themselves. Using the \textsc{NewHorizon} cosmological simulation (40
pc spatial resolution), we investigate how mergers and fly-bys drive the mass
assembly and structural evolution of around 1000 field and group dwarfs up to
z=0.5. We find that, while dwarf galaxies often exhibit disturbed morphologies
(5 and 20 per cent are disturbed at z=1 and z=3 respectively), only a small
proportion of the morphological disturbances seen in dwarf galaxies are driven
by mergers at any redshift (for 10^9 Msun, mergers drive only 20 per cent
morphological disturbances). They are instead primarily the result of
interactions that do not end in a merger (e.g. fly-bys). Given the large
fraction of apparently morphologically disturbed dwarf galaxies which are not,
in fact, merging, this finding is particularly important to future studies
identifying dwarf mergers and post-mergers morphologically at intermediate and
high redshifts. Dwarfs typically undergo one major and one minor merger between
z=5 and z=0.5, accounting for 10 per cent of their total stellar mass. Mergers
can also drive moderate star formation enhancements at lower redshifts (3 or 4
times at z=1), but this accounts for only a few per cent of stellar mass in the
dwarf regime given their infrequency. Non-merger interactions drive
significantly smaller star formation enhancements (around two times), but their
preponderance relative to mergers means they account for around 10 per cent of
stellar mass formed in the dwarf regime.
