Galaxy and Mass Assembly (GAMA): Witnessing the Assembly of the Cluster ABELL 1882

Abstract

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 $v_{{\rm los}} \sim -428^{+187}_{-139}$ km s–1. The primary system, A1882A, has velocity dispersion $\sigma _v=500_{-26}^{+23}$ 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 $\sigma _v=457^{+108}_{-101}$ 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 (M 500 = 1.5-1.9 × 1014 M ☉) when compared with A1882B (M 500 = 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 fb = 0.28 ± 0.09 and 0.18 ± 0.07 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.