Recently, two radio galaxies with 3 have been shown to have large Faraday rotation in their rest frame. The magnitude of the rotation measure is similar to that in nearby cooling flow clusters. These radio galaxies may be located in the centers of similar dense clusters, or the environments of more isolated systems at high redshift may enveloped in a strong magnetic field. Current arguments suggest that very massive clusters would not have formed at such high redshifts, so the second possibility may be favored. In this case, magnetic fields may play an important part in galaxy formation.
Our study of this phenomena is limited by the decrease in the rest frame Faraday rotation by . The 2.4 GHz band is important to provide the frequency coverage to measure the reduced rotation measures. Sensitivity is important because of the low net polarizations from these sources. Resolution plus sensitivity is also critical to prevent the change in rotation measure across these sources from canceling out the polarization signal. Of course, the more resolution we have the more we can learn about the geometry of these fields. Thus once again polarization and the upgrade are important to studies of magnetic fields in high-z objects.