Title：Discovery of a distant X-ray galaxy cluster 2.5 billion years after the Big Bang

　　Speaker：Tao Wang(CEA/Saclay，France)

　　Abstract：Galaxy clusters trace the densest environment and the most massive dark matter halos, hence are ideal laboratories to study environmental effects on galaxy evolution. In this talk I will present our recent discovery of a remarkable concentration of massive galaxies with extended X-ray emission at z=2.506. The velocity dispersion of its member galaxies, the luminosity of the extended X-ray emission, and the high stellar mass content all point to a collapsed dark matter halo with total mass 10^14 M⊙, making it the most distant X-ray detected cluster known to date. Furthermore, unlike other clusters discovered so far, this structure is dominated by star-forming galaxies in the core with a combined star formation rates of ~3400M⊙/yr (as revealed by Herschel, IRAM-NOEMA, JVLA and ALMA observations), providing a rare chance to witness the rapid build-up of a dense cluster core. The rich data set available for this cluster enables a most comprehensive study of gas content, star formation and structural properties of cluster galaxies at the earliest formation epoch. I will discuss the implications of this study on the (trans)formation mechanisms of cluster ellipticals, and how it challenges our current understanding of massive cluster formation.

　　时间：2015年06月30日（星期四）上午10:30

　　地点：紫台317会议室

欢迎大家积极参加！

                                                       紫金山天文台学术委员会