The radio/optical alignment of high-z radio galaxies: triggering of star formation in radio lobes

A young galaxy would contain clouds or filaments with $$T\lesssim10^4$$ K in pressure balance with a medium at $$T\gtrsim10^6$$ K. When activity in its nucleus turns such a galaxy into a strong radio source, shocks propagate through this two-phase gas, inflating radio lobes filled with relativistic plasma. The shocks expel the hot-phase gas, but leave the clouds within the lobes where they are squeezed by the higher pressure. This compression pushes many clouds over the threshold for gravitational instability, thereby triggering a burst of star formation. This process may account for the recently discovered alignment of optical and radio structure in high-z radio galaxies.