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-Riley type I (FR I) galaxy 3C 449, by observing with the VLA at three frequencies (330, 1445, and 4835 MHz) and in all four configurations 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 flows outward, expands, and bends downstream. We find that 3C 449 is more complicated than that, with evidence for a different type of structure, more reminiscent of higher luminosity FR II galaxies. We introduce a new analysis tool-the spectral tomography gallery-and find evidence for two spectral components that we label the "flat jet" and the "sheath." The flat jet remains fairly well collimated throughout the inner 5′, with the sheath accounting for most of the observed widening. The flat 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 flat jet and those in the sheath. Another possibility is that the sheath has a steeper injection index than the flat jet. This may mean that the sheath and flat jet are separate electron populations. In either case, the standard aging analyses would give incorrect answers because of confusion between the separate spectral components.