Fluid dynamical twisting of the radio jets in 3C 449

The jet structure of the double jets in the radio galaxy 3C 449 can be understood as resulting from helical instability of an initially cylindrically symmetric straight jet. A growing helical wave is convected out along the jets and reaches large amplitude at the position of the radio lobes disrupting well-directed flow. Adiabatic expansion of the thermalized jet material produces the radio lobes. The extended diffuse emission outside the present radio lobes is the remnant of earlier more luminous jets. Conditions in the expanding jets required for this mechanism to operate are almost the same as those inferred by Perley, Willis, and Scott from their VLA observations. The jets are supersonic with Mach number on the order of 10 and the flow velocity is about 1500 km s-1. The density of the interstellar medium in the galaxy is inferred to be about the same as the jets' density. The age of the radio source is probably less than several times 108 yr