Absorbers and Globular Cluster Formation in Powerful High Redshift Radio Galaxies

Abstract

A radiative hydrodynamic simulation for a typical, powerful high redshift radio galaxy is presented. The jet is injected at one third the speed of light into a 10 000 times denser, homogeneous medium. In the beginning of the simulation, the bow shock consists of a spherical shell that is similar to a spherical blast wave. This shell cools radiatively down to ${\approx}10^4$ K, providing after $6 \times 10^6$ yrs a neutral column of $3.8 \times 10^{21}\,\mathrm{cm}^{-2}$ around the whole system. The shell starts to fragment and forms condensations. This absorbing screen will cover a smaller and smaller fraction of the radio source, and therefore the emission line region, and eventually form stars in typically 104 globular clusters of $10^6 \ M_\odot$. Approximately $10^9 \ M_\odot$ are entrained into the radio cocoon. This gas, cooling and illuminated from the radio source, could be the emission line gas observed in high redshifted radio galaxies and radio loud quasars. The neutral column behind the bow shock can account for the absorption found in almost all of the small sources. The globular cluster excess of ${\approx}10^4$ systems found in present day brightest cluster galaxies (BCGs), which are believed to be the vestiges of these objects, is consistent with the presented scenario.