Galaxy and Mass Assembly (GAMA): The GAMA Galaxy Group Catalogue (G3Cv1)
  Using the complete GAMA-I survey covering ~142 sq. deg. to r=19.4, of which
~47 sq. deg. is to r=19.8, we create the GAMA-I galaxy group catalogue (G3Cv1),
generated using a friends-of-friends (FoF) based grouping algorithm. Our
algorithm has been tested extensively on one family of mock GAMA lightcones,
constructed from Lambda-CDM N-body simulations populated with semi-analytic
galaxies. Recovered group properties are robust to the effects of interlopers
and are median unbiased in the most important respects. G3Cv1 contains 14,388
galaxy groups (with multiplicity >= 2$), including 44,186 galaxies out of a
possible 110,192 galaxies, implying ~40% of all galaxies are assigned to a
group. The similarities of the mock group catalogues and G3Cv1 are multiple:
global characteristics are in general well recovered. However, we do find a
noticeable deficit in the number of high multiplicity groups in GAMA compared
to the mocks. Additionally, despite exceptionally good local spatial
completeness, G3Cv1 contains significantly fewer compact groups with 5 or more
members, this effect becoming most evident for high multiplicity systems. These
two differences are most likely due to limitations in the physics included of
the current GAMA lightcone mock. Further studies using a variety of galaxy
formation models are required to confirm their exact origin.
