The physics of jets in FR I radio galaxies

We model jets in low-luminosity (FR I) radio galaxies as intrinsically symmetrical, axisymmetric, decelerating relativistic flows with transverse velocity gradients. This allows us to derive velocity fields and the three-dimensional distributions of magneticfield ordering and rest-frame emissivity. A conservation-law analysis, combining the kinematic model with X-ray observations of the surrounding IGM, gives the profiles of internal density, pressure, Mach number and entrainment rate along the jets. We summarize our recently-published results on 3C 31 and outline new work on other sources and adiabatic jet models.