A massive, cooling-flow-induced starburst in the core of a luminous cluster of galaxies

Abstract

In the cores of some galaxy clusters the hot intracluster plasma is dense enough that it should cool radiatively in the cluster_s14s lifetime, leading to continuous _s15cooling flows_s15 of gas sinking towards the cluster center, yet no such cooling flow has been observed. The low observed star formation rates and cool gas masses for these _s15cool core_s15 clusters suggest that much of the cooling must be offset by astrophysical feedback to prevent the formation of a runaway cooling flow. Here we report X-ray, optical, and infrared observations of the galaxy cluster SPT-CLJ2344-4243 at z = 0.596. These observations reveal an exceptionally luminous (L_2-10 keV = 8.2 x 10^45 erg/s) galaxy cluster which hosts an extremely strong cooling flow (dM/dt = 3820 _s16/- 530 Msun/yr). Further, the central galaxy in this cluster appears to be experiencing a massive starburst (740 _s16/- 160 Msun/yr), which suggests that the feedback source responsible for preventing runaway cooling in nearby cool core clusters may not yet be fully established in SPT-CLJ2344-4243. This large star formation rate implies that a significant fraction of the stars in the central galaxy of this cluster may form via accretion of the intracluster medium, rather than the current picture of central galaxies assembling entirely via mergers.