In this thesis we have presented results related to the optical morphology of a sample of radio galaxies from the MRC. The motivation of the thesis has been to identify morphologically peculiar features in radio galaxies and to try and relate them to the activity in these galaxies. The project had its modest roots in looking for dust features in radio galaxies following our finding a dust lane in NGC 4261 (Mahabal et al., 1996).
It was soon realized that the profile fits are a great information
resource. We were able to devise different ways to make use of the
information to study the profile shapes as well as the galaxy
components.
de Vaucouleurs' law, though empirical in nature, provides an excellent base fit to
normal ellipticals as well as radio ellipticals. de Vaucouleurs' law has been
extensively used in literature. However, most authors tend to use
the parameters in a single photometric band. By studying parameters in
more than one band, we have shown that
the distribution of the 
ratio is a powerful indicator
of possible activity in a galaxy. Using the distribution of
this ratio for the radio
galaxies, and a control sample of early type galaxies,
we were able to show that the
radio galaxies are likely to have undergone recent star formation
in the central region whereas the control galaxies had a quiet
history.
We have presented a simple relation between the scale length ratio and the color gradient. Gradients obtained in this manner are well correlated with conventionally measured color gradient, so the scale length ratio itself can be used as a color indicator. We have found that the ratio is more robust than the conventional gradient, in the sense that it can be used even when the color profile is too noisy for the conventional color gradient to be useful.
Observations of a large number of galaxies have indicated that
de Vaucouleurs' law is valid in the interval 
(Burkert, 1993).
For 
one expects departures from the law. The spreading
due to the
PSF also makes it difficult to reliably obtain values close to
the center.
Hence we have carried out all fits by leaving out
points within 1.5 times the FWHM of the PSF from the center.
After obtaining the fit we have looked for
deviations from de Vaucouleurs' law in the profile close to the center
by comparing the observed profile with extrapolation of the model profile
right up to the center.
Our investigations indicate that for
almost all control sample galaxies de Vaucouleurs' law is valid close to
the center in the sense that the observed points lie within
of the extrapolated model. The radio galaxies, on the other
hand reveal excess
emission in 
of cases as compared to 
of the
control sample galaxies.
We attribute the excess emission to starburst. A deficit relative
to the extrapolation, indicating absorption due to dust is found in
of the radio sample and 
of the control sample
(see Table 
).
We find that 
of the radio galaxies
exhibit some form of morphological peculiarity with FR II galaxies
exhibiting a peculiarity more frequently ( 
) than the
FR I galaxies ( 
).
A small note on individual galaxies is presented in
Appendix . A disk in a radio galaxy is supposed to be
particularly rare. In our sample, we have detected five ( 
)
disky candidates. One of them clearly possesses spiral-like
structure where as two others show some indication of such
structures. To help us detect faint
disks (or, for that matter, any faint source hidden on top of a
background for which an empirical formula is available) we have developed
a series of morphological filters. The morphological gradient filter
is able to detect changes in contrast and using it
we are able to see spiral-like structure in two
galaxies. None of the disky galaxies is an FR I source.
We find that 
radio galaxies
have dust lanes and have prominent dust patches.
In the control sample there are fewer galaxies with dust lanes
but more with patchy dust, indicating that the dust in radio
galaxies is more coherent. The dust content estimated from
extrapolated profiles indicates that in nuclear regions radio
galaxies are more likely to have dust. We found that the dust mass in
dust lane galaxies is proportional to the radio power at 408 MHz.
One of the surprises of the study was our finding that the dust lanes are, in general, not perpendicular to the radio axis. Earlier studies had suggested that the two tend to be perpendicular (e.g. Kotanyi and Ekers, 1979; Möllenhoff et al., 1992; van Dokkum and Franx, 1995). Our numbers are small and it could be that it is just a statistical effect. However, it is a result worth keeping in mind.
We find that 
FR I galaxies contain dust while only
FR II galaxies are dusty. The incidence of isophotal
twists and secondary nuclei is comparable in FR I and FR II
radio galaxies. FR II galaxies tend to possess disky isophotes
whereas FR I galaxies tend to possess boxy isophotes.
It is likely
that in some of the FR II sources are inducing star formation along the
path of the radio source. Similarly, a higher incidence of blue
centers is seen in FR II galaxies.
To summarize, the optical morphology of radio galaxies indicates that these galaxies are not smooth, classical ellipticals but frequently contain morphologically peculiar features. They are characterized by bluer centers very likely to be related to star formation in the recent past. Contrary to previous beliefs, radio galaxies can contain disks too. It is FR II galaxies that are seen to contain a higher frequency of morphological peculiarities and disks. FR I galaxies are more likely to contain dust. Dust in radio galaxies is more likely to be coherent.
These findings point to a number of possible future studies. We discuss some of these in the next section.