Transverse motions in CSOs?

The measurement of proper motions in CSOs is a powerful tool to determine the dynamical evolution of the newly born extragalactic radio sources. We observed 3 CSOs with the VLBA in 2004 and in 2006 to monitor changes in their structure and measure the separation velocity of the hot spots. It is important to increase the size of the samples of CSOs with measured expansion velocity to test the existence of frustrated objects, and put stringent constraints on the current models. We found for all the three objects observed a transverse motion of the hot-spots, and we suggest as the more likely explanation a precession in the jet axis. This behaviour likely inhibits or at least slows down the radio source growth because the head of the hot-spot continuously hits new regions of the ISM. Therefore these radio sources may represent an old population of GPS/CSOs.