Contrary to previous interpretations, we suggest that the anomalous
arms in NGC 4258 trace the gas flow due to a bar rather
than being the manifestation of a jet. Both the S-shaped morphology
and the velocity dispersion revealed by the present CO measurements
are characteristic of barred galaxies. In the bar of NGC 4258
most of the gas is molecular, not atomic. The molecular gas is bounded
by the sharp leading edge traced in the radio continuum that
is probably the bar shock with its compressed magnetic field.
The shocked H emission along the anomalous arms is probably
a secondary manifestation of the bar shock. In the
X-ray emitting gas associated with the anomalous arms,
the temperature is consistent
with velocities and densities in bar shock fronts rather than in jets of
radio galaxies. We suggest that the X-rays, like the radio continuum
and optical line emission, are produced via the bar shock, and are
unrelated to a jet from the black hole. The large extension of both the
H
and radio emissions out to a projected distance
of
kpc probably trace the hot (
K)
thermal X-ray gas produced by the bar
shocks which leaks out of the bar structure and eventually escapes
from the disk in the z direction. We predict that with sufficient
sensitivity and angular resolution, similar radio and X-ray
emission will also be found in the shock fronts of
other, more distant, barred galaxies.