As per the original classification of Hubble, elliptical galaxies
were entirely dust free. If observations indicated that a galaxy
contained some amount of dust, it was classified as an S0 or later type.
High dynamic range imaging and improved detection techniques over
the last several years have indicated
that even classical elliptical galaxies can contain dust.
Sadler and Gerhard (1985) showed that
this is true with 
of ellipticals.
More recently, van Dokkum and Franx (1995) have
inferred from a study based on HST observations that
early-type galaxies contain nuclear dust.
Though the dust can be in patchy structures, the more interesting and frequently found configuration is that of a disk. Disks are seen in the form of a dust lane when viewed nearly edge-on. Face on dust disks are likely to go unnoticed unless the optical depth is sufficiently large.
A dust lane can be potentially useful in providing information about the 3D shape of the host galaxy. Elliptical galaxies are dynamically supported by the anisotropy in velocity dispersion rather than rotation (Bertola and Capaccioli, 1975; Illingworth, 1977). This results in the galaxy being triaxial rather than axisymmetric (Binney, 1976). Schwarzschild (1979) has shown that closed stable orbits in a triaxial system exist in the planes perpendicular to the short and long axes of the system. Orbits in a plane perpendicular to the intermediate axis are unstable and a gaseous disk in that orientation will not last. Thus, when a dust lane is seen, the possibilities for the 3D shape of the galaxy narrow down. If an elliptical is spheroidal, a minor-axis dust lane will mean that the galaxy is prolate and a major-axis dust lane that it is oblate (see, e.g. Kormendy and Djorgovski, 1989).
The situation is, however, complicated by the following facts: (1) elliptical galaxies are, in general, triaxial, (2) the dust lane, if of external origin, could be the result of gas trapped in a polar orbit and (3) the galaxy can have some amount of rotation. Observations indicate that many dust lanes are warped in the outer region indicating that the dust in the inner parts is settled in a preferred plane but the dust in the outer parts has not settled into an equilibrium plane yet. This further indicates that the dust is of an external origin. The most plausible explanation is a merger. There is kinematic evidence indicating that dust disks are often at random orientations with respect to the major axis (e.g.\ Gallagher et al., 1977) and can even be counterrotating.
Radio galaxies with dust lanes are even more interesting since in
addition to the dust lane, we have the radio
axis to provide us directional information. Kotanyi and Ekers
(1979) showed after studying a sample of 8 radio ellipticals with
dust lanes that there is a strong tendency of
the dust lane to be perpendicular to the radio source.
Following studies of a sample of 26 elliptical galaxies with
prominent dust lanes Möllenhoff et al. (1992) have
further confirmed that there exists a strong tendency for the radio
axis to be aligned perpendicular to the dust lane whereas the angle
between the radio axis and the major axis of the galaxy is consistent
with being random. Though the
accretion disk associated with the AGN need not be
aligned with the stellar body or the large scale gaseous disk, it
seems that it nevertheless is associated with the latter.
In fact, it was seen that 21 of these 26 dust lane ellipticals
were radio emitters ( 
)
suggesting that the existence of a dust lane itself may be very closely
related to the host galaxy being a radio galaxy. The selection criterion
for this sample was simply that each galaxy contain a prominent dust lane.
For normal ellipticals,
the rate of radio detection is much smaller (64/216; Wrobel
and Heeschen, 1991).
Dust lanes have been one of the more important triggers for the
study that we present in this thesis.
In this chapter we present
the dust configuration and morphology of various galaxies in the
radio sample with a particular emphasis on the six galaxies where
we detect dust lanes. In Section 
we describe the various
techniques that we have used for detecting dust, in Section
we present details of the dust lane galaxies in the sample and provide
various related details including the estimated
mass of dust and extinction coefficient.
Finally we discuss the orientations and intrinsic shapes.