Fluid Flow and Spectral Aging in Tailed Radio
J. A. Eilek
Two-frequency surface brightness measurements of radio tails can be
used to infer the evolution of velocity, magnetic field and
relativisitic particle density in these tails. This information can
then be used to determine the age of plasma as a function of distance
down the tail. I apply these methods to a set of 12 radio tails from
O'Donoghue's Wide-Angle Tailed source survey. I find a characteristic
velocity law, which is not easily explained by current subsonic jet
models. I also that the plasma in the tails evolves away from
equipartion, in that it becomes more magnetized farther down the tail.
I also find that the rate of decay of the cutoff frequency is much
slower than predicted by standard synchrotron aging theory. This
means that the cutoff frequency cannot be used to measure the source
age: the sources are older than they look.
STATUS: submitted to Ap.J.