  High-redshift radio galaxies present signs of both star formation and AGN
activity, making them ideal candidates to investigate the connection and
coevolution of AGN and star formation in the progenitors of present-day massive
galaxies. We make use of a sample of 11 powerful radio galaxies spanning 1<z<4
which have complete coverage of their spectral energy distribution (SED) from
UV to FIR wavelengths. Using Herschel data, we disentangle the relative
contribution of the AGN and star formation by combining the
galaxyevolutioncodePEGASE.3 with an AGN torus model. We find that three
components are necessary to reproduce the observed SEDs: an evolved and massive
stellar component, a submm bright young starburst, and an AGN torus. We find
that powerful radio galaxies form at very high-redshift, but experience
episodic and important growth at 1<z<4 as the mass of the associated starburst
varies from 5 to 50% of the total mass of the system. The properties of star
formation differ from source to source, indicating no general trend of the star
formation properties in the most infrared luminous high-redshift radio galaxies
and no correlation with the AGN bolometric luminosity. Moreover, we find that
AGN scattered light have a very limited impact on broad-band SED fitting on our
sample. Finally, our analysis also suggests a wide range in origins for the
observed star formation,which we partially constrain for some sources.
