The nature of the extreme kinematics in the extended gas of high redshift radio galaxies

We present UV rest frame spectra of 3 powerful narrow line radio galaxies a nd the hyperluminous type 2 active galaxy SMM J02399-0136, all at high reds hift (z > 2). We find high velocities (FWHM > 1000 km s(-1)) in the extende d gas of all objects. A natural explanation is the interaction between the radio jet and the ambient gas, that drives shocks into the gas and accelera tes the clouds. However, the existence of high velocities in regions where such interactions are not taking place implies that other processes can pla y a role. We discuss here several possible mechanisms.