Cosmology Seminar: Francesco Valentino
Francesco Valentino is a DAWN fellow at the Cosmic Dawn Centre, and a DARK Fellow at the DARK Cosmology Centre, both at the Niels Bohr Institute, Copenhagen University.
Giant Lyman-alpha nebulae in high-redshift clusters of galaxies
We report the discovery of a giant Lya nebula detected with Keck/LRIS narrow-band imaging in the core of one of the farthest known X-ray emitting clusters, CL J1449+056 at z=1.99. To our knowledge, this is the first case of a giant Lya nebula observed along with a 10^7 K medium permeating the core of a cluster at high-z. The most plausible candidates to power the Lya emission are two bright Chandra-detected AGN in the cluster core. Cooling from the X-ray phase as observed in local cool-core clusters may partially contribute to the nebular emission, but a straight comparison with low-z systems reveals clear inconsistencies. We study the interaction between the Lya-emitting cold gas and the hot intracluster medium, finding that the nebula should evaporate on <10 Myr timescale, if not replenished with cold gas. Barring an improbable observational coincidence, we pinpoint the generous outflows from cluster members (>1000 Msun/yr) as a plausible source for gas replenishment. Moreover, outflows inject a prodigious amount of kinetic energy into the intracluster medium, as theoretically requested to solve a decade-standing problem in astrophysics: the thermodynamical properties of local massive clusters. We argue that Lya nebulae in cluster cores at high-z might trace this energy injection, providing new crucial empirical constraints on the process.