An extreme case of galaxy and cluster co-evolution at z  = 0.7

Abstract

We report the discovery of eMACS J0252.4−2100 (eMACS J0252), 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 [O ii] 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 (1.9 ± 0.1) × 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 eMACS J0252 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 haloes and baryons in the era of cluster formation.

The strongest cool core in REXCESS: Missing X-ray cavities in RXC J2014.8–2430

“…These observations showed that in most relaxed clusters the strong X-ray emission lines from gas around 10 7 K (∼0.9 keV) predicted by the simple cooling flow model were generally not present at their predicted strengths. However, there has been growing evidence for molecular gas cooling directly onto the central galaxy (Hamer et al 2012), and notable exceptions supporting the existence of true cooling flows have been found over the last decade; examples include the Phoenix Cluster (McDonald et al 2012), SpARCS J104922.6+564032.5 (Hlavacek-Larrondo et al 2020), and eMACS J0252.4-2100 (Ebeling et al 2021), which all have star formation rates of several hundred M yr −1 in their BCGs. In the case of the Phoenix Cluster, Russell et al (2017) showed through Atacama Large Millimeter/submillimeter Array (ALMA) observations that the mass in molecular gas is similar to that in other cool-core clusters, indicating that the salient distinction of a cooling flow may be the star formation rate rather than the amount of cold molecular gas.…”