On the properties of compact groups identified in different photometric
  bands
  Historically, compact group catalogues vary not only in their identification
algorithms and selection functions, but also in their photometric bands.
Differences between compact group catalogues have been reported. However, it is
difficult to assess the impact of the photometric band in these differences
given the variety of identification algorithms. We used the mock lightcone
built by Henriques et al. (2012) to identify and compare compact groups in
three different photometric bands: $K$, $r$, and $u$. We applied the same
selection functions in the three bands, and found that compact groups in the
u-band look the smallest in projection, the difference between the two
brightest galaxies is the largest in the K-band, while compact groups in the
r-band present the lowest compactness. We also investigated the differences
between samples when galaxies are selected only in one particular band (pure
compact groups) and those that exist regardless the band in which galaxies were
observed (common compact groups). We found that the differences between the
total samples are magnified, but also some others arise: pure-r compact groups
are the largest in projection; pure-u compact groups have the brightest first
ranked galaxies, and the most similar two first ranked galaxies; pure-K compact
groups have the highest compactness and the most different two first ranked
galaxies; and common compact groups show the largest percentage of physically
dense groups. Therefore, without a careful selection and identification of the
samples, the characteristic features of group properties in a particular
photometric band could be overshadowed.
