Galaxy and Mass Assembly (GAMA): The GAMA Galaxy Group Catalogue (G3Cv1)

TL;DR

This paper presents the creation and validation of the GAMA Galaxy Group Catalogue (G3Cv1), derived from the GAMA-I survey, using a friends-of-friends algorithm, and compares its properties with mock catalogues to assess accuracy and limitations.

Contribution

The G3Cv1 catalogue is the first extensive galaxy group catalogue from GAMA-I, employing a robust FoF algorithm validated against simulations, revealing key differences with mock catalogues.

Findings

G3Cv1 contains 14,388 galaxy groups with 44,186 galaxies.

Good recovery of global group properties compared to mocks.

Notable deficit of high multiplicity and compact groups in G3Cv1.

Abstract

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.