  Close pairs of galaxies have been broadly studied in the literature as a way
to understand galaxy interactions and mergers. In observations they are usually
defined by setting a maximum separation in the sky and in velocity along the
line of sight, and finding galaxies within these ranges. However, when
observing the sky, projection effects can affect the results, by creating
spurious pairs that are not close in physical distance. In this work we mimic
these observational techniques to find pairs in The Three Hundred simulations
of clusters of galaxies. The galaxies' 3D coordinates are projected into 2D,
with Hubble flow included for their line-of-sight velocities. The pairs found
are classified into "good" or "bad" depending on whether their 3D separations
are within the 2D spatial limit or not. We find that the fraction of good pairs
can be between 30 and 60 per cent depending on the thresholds used in
observations. Studying the ratios of observable properties between the pair
member galaxies, we find that the likelihood of a pair being "good" can be
increased by around 40, 20 and 30 per cent if the given pair has, respectively,
a mass ratio below 0.2, metallicity ratio above 0.8, or colour ratio below 0.8.
Moreover, shape and stellar-to-halo mass ratios respectively below 0.4 and 0.2
can increase the likelihood by 50 to 100 per cent. These results suggest that
these properties can be used to increase the chance of finding good pairs in
observations of galaxy clusters and their environment.
