[en] We present a combined optical and X-ray analysis of the rich cluster ABELL 1882 (A1882) with the aim of identifying merging substructure and understanding the recent assembly history of this system. Our optical data consist of spectra drawn from the Galaxy and Mass Assembly survey, which lends itself to this kind of detailed study thanks to its depth and high spectroscopic completeness. We use 283 spectroscopically confirmed cluster members to detect and characterize substructure. We complement the optical data with X-ray data taken with both Chandra and XMM. Our analysis reveals that A1882 harbors two main components, A1882A and A1882B, which have a projected separation of ∼2 Mpc and a line of sight velocity difference of v_los∼-428⁺¹⁸⁷_-139 km s^–1. The primary system, A1882A, has velocity dispersion σ_v=500_-26⁺²³ km s^–1 and Chandra (XMM) temperature kT = 3.57 ± 0.17 keV (3.31^+0.28_-0.27 keV) while the secondary, A1882B, has σ_v=457⁺¹⁰⁸_-101 km s^–1 and Chandra (XMM) temperature kT = 2.39 ± 0.28 keV (2.12 ± 0.20 keV). The optical and X-ray estimates for the masses of the two systems are consistent within the uncertainties and indicate that there is twice as much mass in A1882A (M₅₀₀ = 1.5-1.9 × 10¹⁴ M_☉) when compared with A1882B (M₅₀₀ = 0.8-1.0 × 10¹⁴ M_☉). We interpret the A1882A/A1882B system as being observed prior to a core passage. Supporting this interpretation is the large projected separation of A1882A and A1882B and the dearth of evidence for a recent (<2 Gyr) major interaction in the X-ray data. Two-body analyses indicate that A1882A and A1882B form a bound system with bound incoming solutions strongly favored. We compute blue fractions of f_b = 0.28 ± 0.09 and 0.18 ± 0.07 for the spectroscopically confirmed member galaxies within r₅₀₀ of the centers of A1882A and A1882B, respectively. These blue fractions do not differ significantly from the blue fraction measured from an ensemble of 20 clusters with similar mass and redshift

[en] The Galaxy And Mass Assembly (GAMA) survey furnishes a deep redshift catalog that, when combined with the Wide-field Infrared Survey Explorer (WISE), allows us to explore for the first time the mid-infrared properties of >110, 000 galaxies over 120 deg² to z ≅ 0.5. In this paper we detail the procedure for producing the matched GAMA-WISE catalog for the G12 and G15 fields, in particular characterizing and measuring resolved sources; the complete catalogs for all three GAMA equatorial fields will be made available through the GAMA public releases. The wealth of multiwavelength photometry and optical spectroscopy allows us to explore empirical relations between optically determined stellar mass (derived from synthetic stellar population models) and 3.4 μm and 4.6 μm WISE measurements. Similarly dust-corrected Hα-derived star formation rates can be compared to 12 μm and 22 μm luminosities to quantify correlations that can be applied to large samples to z < 0.5. To illustrate the applications of these relations, we use the 12 μm star formation prescription to investigate the behavior of specific star formation within the GAMA-WISE sample and underscore the ability of WISE to detect star-forming systems at z ∼ 0.5. Within galaxy groups (determined by a sophisticated friends-of-friends scheme), results suggest that galaxies with a neighbor within 100 h ^–1 kpc have, on average, lower specific star formation rates than typical GAMA galaxies with the same stellar mass.