AN ANALYSIS OF THE SYNCHROTRON SPECTRUM IN THE FANAROFF-RILEY TYPE-I GALAXY 3C-449

We studied the evolution of relativistic electrons in the Fanaroff-Ril ey type I (FR I) galaxy 3C 449, by observing with the VLA at three fre quencies (330, 1445, and 4835 MHz) and in all four configurations for a primary resolution of 3.'' 6. The conventional model for this type o f source is that the relativistic electrons are accelerated in the cor e and subsequently lose energy as the jet flows outward, expands, and bends downstream. We find that 3C 449 is more complicated than that, w ith evidence for a different type of structure, more reminiscent of hi gher luminosity FR II galaxies. We introduce a new analysis tool-the s pectral tomography gallery-and find evidence for two spectral componen ts that we label the ''flat jet'' and the ''sheath.'' The flat jet rem ains fairly well collimated throughout the inner 5', with the sheath a ccounting for most of the observed widening. The flat jet shows little steepening with distance from the core. However, the sheath has a ste eper spectral index than the jet. If the same spectral shape is approp riate for both components, there may be an evolutionary connection bet ween the particles in the flat jet and those in the sheath. Another po ssibility is that the sheath has a steeper injection index than the fl at jet. This may mean that the sheath and flat jet are separate electr on populations. In either case, the standard aging analyses would give incorrect answers because of confusion between the separate spectral components.