Spectral Structure in FRII Radio Galaxies and Jets

Using spectral tomography to separate overlapping spectral features in a sample of FRII radio galaxies, we find a variety of spatial/spectral features that are not easily described in the context of current models. In particular, we find mixtures of flat and steep spectrum features in the hot spot regions, and non-monotonic spectral index gradients along jets. Additional findings include spectral gradients in compact hot spots and possible transitions in jet properties at the downstream ends of the diffuse lobes. The complexity of behaviors uncovered here points to the need for a thorough investigation of numerical models for radio galaxies, as well as detailed observational studies of larger, unbiased samples. We also perform the first quantitative assessment of errors in the use of spectral tomography for spectral index measurements.