  Observational and theoretical studies of extragalactic radio sources have
suggested that an inhomogeneous environment may be responsible for observed arm
length asymmetries of jets and the properties of extended emission line regions
in high redshift radio galaxies. We perform 3D hydrodynamic simulations of the
interaction of a powerful extragalactic bipolar jet with a disc-shaped clumpy
interstellar medium of log-normal density distribution and analyze the
asymmetry. Furthermore, we compute the relation between jet asymmetry and the
ISM properties by means of Monte Carlo simulations based on a 1D propagation
model for the jet through the dense medium. We find that the properties of the
ISM can be related to a probability distribution of jet arm length asymmetries:
Disc density and height are found to have the largest effect on the asymmetry
for realistic parameter ranges, while the Fourier energy spectrum of the ISM
and turbulent Mach number only have a smaller effect. The hydrodynamic
simulations show that asymmetries generally may be even larger than expected
from the 1D model due to the complex interaction of the jet and its bow shock
with gaseous clumps, which goes much beyond simple energy disposal. From our
results, observed asymmetries of medium-sized local radio galaxies may be
explained by gas masses of 10^9 to 10^10 solar masses in massive elliptical
galaxies. Furthermore, the simulations provide a theoretical basis for the
observed correlation that emission line nebulae are generally found to be
brighter on the side of the shorter lobe in high redshift radio galaxies
(McCarthy et al. 1991). This interaction of jets with the cold gas phase
suggests that star formation in evolving high redshift galaxies may be affected
considerably by jet activity.
