A pan-chromatic view of the galaxy cluster XMMU J1230.3+1339 at z = 0.975. Observing the assembly of a massive system

Context. Observations of the formation and evolution of massive galaxy clusters and their matter components provide crucial constraints on cosmic structure formation, the thermal history of the intracluster medium (ICM), galaxy evolution, transformation processes, and gravitational and hydrodynamic interaction physics of the subcomponents.
Aims: We characterize the global multi-wavelength properties of the X-ray selected galaxy cluster XMMU J1230.3+1339 at z = 0.975, a new system discovered within the XMM-Newton Distant Cluster Project (XDCP). We measure and compare various widely used mass proxies and identify multiple cluster-associated components from the inner core region out to the large-scale structure environment.
Methods: We present a comprehensive galaxy cluster study based on a joint analysis of X-ray data, optical imaging and spectroscopy observations, weak lensing results, and radio properties for achieving a detailed multi-component view on a system at z 1.
Results: We find an optically very rich and massive system with M₂₀₀ ≃ (4.2 ± 0.8) × 10¹⁴ M_⊙, T_{X,2500 ≃ 5.3^+0.7_-0.6} keV, and L^bol_X,500 ≃ (6.5 ± 0.7) × 10⁴⁴ erg s^-1. We have identified a central fly-through group close to core passage and find marginally extended 1.4 GHz radio emission possibly associated with the turbulent wake region of the merging event. On the cluster outskirts we see evidence for an on-axis infalling group with a second brightest cluster galaxy (BCG) and indications for an additional off-axis group accretion event. We trace two galaxy filaments beyond the nominal cluster radius and provide a tentative reconstruction of the 3D-accretion geometry of the system. Conclusions: In terms of total mass, ICM structure, optical richness, and the presence of two dominant BCG-type galaxies, the newly confirmed cluster XMMU J1230.3+1339 is likely the progenitor of a system very similar to the local Coma cluster, differing by 7.6 Gyr of structure evolution. This new system is an ideally suited astrophysical model laboratory for in-depth follow-up studies on the aggregation of baryons in the cold and hot phases.

Based on observations obtained with ESO Telescopes at the Paranal Observatory under program ID 078.A-0265 and 081.A-0312, and observations with the Large Binocular Telescope (LBT), and the X-ray observatories XMM-Newton and Chandra.