Galaxy and Mass Assembly (GAMA): Witnessing the assembly of the cluster
  Abell 1882
  We present a combined optical and X-ray analysis of the rich cluster Abell
1882 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 (GAMA) 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 2Mpc
and a line of sight velocity difference of v_{los}=-428km/s. The primary
system, A1882A, has velocity dispersion sigma_v=500km/s and Chandra (XMM)
temperature kT=3.57keV (3.31keV) while the secondary, A1882B, has
sigma_v=457km/s and Chandra (XMM) temperature kT=2.39keV (2.12keV). 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
(M_{500}=1.5-1.9x10^{14}Msolar) when compared with A1882B
(M_{500}=0.8-1.0x10^{14}Msolar). 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 (<2Gyr) 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 and 0.18 for the
spectroscopically confirmed member galaxies within r_{500} 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.
