Galaxy and Mass Assembly (GAMA): the GAMA galaxy group catalogue (G3Cv1)

Using the complete Galaxy and Mass Assembly I (GAMA-I) survey covering˜142 deg2 to rAB= 19.4, of which ˜47deg2 is to rAB= 19.8, we create the GAMA-I galaxygroup catalogue (G3Cv1), generated using a friends-of-friends(FoF) based grouping algorithm. Our algorithm has been testedextensively on one family of mock GAMA lightcones, constructed fromΛ cold dark matter N-body simulations populated withsemi-analytic galaxies. Recovered group properties are robust to theeffects of interlopers and are median unbiased in the most importantrespects. G3Cv1 contains 14 388 galaxy groups (withmultiplicity ≥2), including 44 186 galaxies out of a possible 110 192galaxies, implying ˜40 per cent of all galaxies are assigned to agroup. The similarities of the mock group catalogues andG3Cv1 are multiple: global characteristics are in generalwell recovered. However, we do find a noticeable deficit in the numberof high multiplicity groups in GAMA compared to the mocks. Additionally,despite exceptionally good local spatial completeness, G3Cv1contains significantly fewer compact groups with five or more members,this effect becoming most evident for high multiplicity systems. Thesetwo differences are most likely due to limitations in the physicsincluded of the current GAMA lightcone mock. Further studies using avariety of galaxy formation models are required to confirm their exactorigin. The G3Cv1 catalogue will be made publicly availableas and when the relevant GAMA redshifts are made available at http://www.gama-survey.org..