An Analysis of the Synchrotron Spectrum in the Fanaro - RileyType I Galaxy 3

We studied the evolution of relativistic electrons in the Fanaroo-Riley Type I (FR I) galaxy 3C449, by observing with the VLA at three frequencies (330, 1445 and 4835 MHz) and in all 4 conngurations for a primary resolution of 3."6. The conventional model for this type of source is that the relativistic electrons are accelerated in the core and subsequently lose energy as the jet ows outward, expands and bends downstream. We nd that 3C449 is more complicated than that with evidence for a diierent type of structure, more reminiscent of higher luminosity FR II galaxies. We introduce a new analysis tool-the spectral tomography gallery-and nd evidence for two spectral components that we label the \\at jet" and the \sheath". The at jet remains fairly well collimated throughout the inner 5 arcminutes, with the sheath accounting for most of the observed widening. The at jet shows little steepening with distance from the core. However, the sheath has a steeper spectral index than the jet. If the same spectral shape is appropriate for both components, there may be an evolutionary connection between the particles in the at jet and those in the sheath. Another possibility is that the sheath has a steeper injection index than the at jet. This may mean that the sheath and at jet are separate electron populations. In either case, the standard aging analyses would give incorrect answers because of confusion between the separate spectral components.