An extreme case of galaxy and cluster co-evolution at z=0.7
Abstract
We report the discovery of eMACSJ0252.4-2100 (eMACSJ0252), a massive and highly evolved galaxy cluster at z=0.703. Our analysis of Hubble Space Telescope imaging and VLT/MUSE and Keck/DEIMOS spectroscopy of the system finds a high velocity dispersion of 1020+180-190 km s-1 and a high (if tentative) X-ray luminosity of (1.2 0.4)×1045 erg s-1 (0.1-2.4 keV). As extreme is the system's brightest cluster galaxy, a giant cD galaxy that forms stars at a rate of between 85 and 300 M yr-1 and features an extended halo of diffuse [OII] emission, as well as evidence of dust. Its most remarkable properties, however, are an exceptionally high ellipticity and a radially symmetric flow of gas in the surrounding intracluster medium, potential direct kinematic evidence of a cooling flow. A strong-lensing analysis, anchored by two multiple-image systems with spectroscopic redshifts, finds the best lens model to consist of a single cluster-scale halo with a total mass of (1.90.1)× 1014 M within 250 kpc of the cluster core and, again, an extraordinarily high ellipticity of e=0.8. Although further, in-depth studies across the electromagnetic spectrum (especially in the X-ray regime) are needed to conclusively determine the dynamical state of the system, the properties established so far suggest that eMACSJ0252 must have already been highly evolved well before z 1, making it a prime target to constrain the physical mechanisms and history of the co-evolution or dark-matter halos and baryons in the era of cluster formation.