6.3. The Northwest Jet
Unlike the SE jet, the NW jet shows no evidence for helical
strands. Nevertheless,
there is clear evidence for significant kinematic disturbance by the NW
jet at both small and large nuclear distances
(Figs 4c and
d). The observed recession
velocities along the
NW jet tend to follow those of the disk rotation, but are systematically
redshifted by
80 km s-1, on
average, from those of the surrounding gas
(see Fig. 18 of CWT). As
for the SE jet, this is clear evidence for interaction between the jet
and interstellar gas
in the galaxy disk. Even more striking is the relationship between the
inner part (d 
1 kpc) of the NW jet and molecular cloud complexes
(Fig. 7). The Fabry-Perot data
show direct evidence for confinement of the jet by molecular gas,
revealing a stream
of high velocity gas between the CO-observed clouds. Furthermore, the
jet seems to
be deflected by the molecular gas at three, or possibly four,
locations. The deflections are characterized by localized brightenings in
H
- knots a, b, c and d
in Fig. 7. These
knots each contain a few x 104
M
(1
cm-3/ne) of ionized gas and may result from
internal shocks (e.g.,
Icke 1991).
The interaction with CO cloud nr. 2 (Fig. 7) may
accelerate this molecular cloud to a velocity of several hundred km
s-1 according to
Plante et al. (1991).
These jet deflections and accelerations of interstellar clouds are
reminiscent of the similar processes occurring in powerful radio
galaxies (Section 3).
|
Figure 7. (from
Cecil, Wilson &
Tully 1992).
The interaction between the NNW jet
of NGC 4258 and dense molecular cloud complexes. The
nucleus is at the cross and
the ticks are at 5 arc sec intervals. (a) A gray-scale plot of the
recession velocity of
H |