Spectral structure in FR II radio galaxies and jets

Using spectral tomography to separate overlapping spectral features in a sa mple of FR II radio galaxies, we find a variety of spatial/spectral feature s that are not easily described in the context of current models. In partic ular, we find mixtures of flat- and steep-spectrum features in the hot spot regions and nonmonotonic spectral index gradients along jets. Additional f indings include spectral gradients in compact hot spots and possible transi tions in jet properties at the downstream ends of the diffuse lobes. The co mplexity of behaviors uncovered here points to the need for a thorough inve stigation of numerical models for radio galaxies, as well as for detailed o bservational studies of larger, unbiased samples. We also perform the first quantitative assessment of errors in the use of spectral tomography for sp ectral index measurements.