Evolution of the aligned structures in z ∼ 1 radio galaxies

Hubble Space Telescope observations are presented of eight 3CR radio galaxies in the redshift interval l≾z≾1.3. The optical morphologies of these galaxies change dramatically as the radio size increases. It is shown that this evolution is entirely consistent with large-scale star formation induced by the radio jet, and it is argued that this mechanism could be the predominant cause of the observed alignment of the optical emission along the radio axis.