  Galaxy mergers are crucial to understanding galaxy evolution, therefore we
must determine their observational signatures to select them from large IFU
galaxy samples such as MUSE and SAMI. We employ 24 high-resolution idealised
hydrodynamical galaxy merger simulations based on the "Feedback In Realistic
Environment" (FIRE-2) model to determine the observability of mergers to
various configurations and stages using synthetic images and velocity maps. Our
mergers cover a range of orbital configurations at fixed 1:2.5 stellar mass
ratio for two gas rich spirals at low redshift. Morphological and kinematic
asymmetries are computed for synthetic images and velocity maps spanning each
interaction. We divide the interaction sequence into three: (1) the pair phase;
(2) the merging phase; and (3) the post-coalescence phase. We correctly
identify mergers between first pericentre passage and 500 Myr after coalescence
using kinematic asymmetry with 66% completeness, depending upon merger phase
and the field-of-view of the observation. We detect fewer mergers in the pair
phase (40%) and many more in the merging and post-coalescence phases (97%). We
find that merger detectability decreases with field-of-view, except in
retrograde mergers, where centrally concentrated asymmetric kinematic features
enhances their detectability. Using a cut-off derived from a combination of
photometric and kinematic asymmetry, we increase these detections to 89%
overall, 79% in pairs, and close to 100% in the merging and post-coalescent
phases. By using this combined asymmetry cut-off we mitigate some of the
effects caused by smaller fields-of-view subtended by massively multiplexed
integral field spectroscopy programmes.
