In this thesis we have studied 30 radio galaxies from the Molonglo Reference Catalogue (MRC) which have a redshift ;SPMlt;0.3. A brief description of the work has been presented in the abstract. Here we take a look at the contents from the point of view of new achievements.
The main objective of the thesis has been to study the
optical and near infrared morphology
of radio galaxies.
In the course of the work we have shown that radio galaxies
do not have highly distorted morphology. Their
surface brightness profiles can, in 
of the cases,
be fit rather well by a de Vaucouleurs' law model, with the addition, in some
cases, of a significant disk component. The good fits are
obtained right upto the maximum redshift of 0.3 of our sample.
Over half the radio galaxies show morphological peculiarities
superposed on the rather regular large scale distribution
of light. The peculiarities occur more frequently in case of the
radio galaxies than they do for the control sample galaxies.
>From our model profile fits to the observed
surface brightness profiles
we have found that the distribution of the ratio of de Vaucouleurs scale
lengths in the 
bands 
is different for the
two samples.
A value ;SPMlt;1 for this ratio indicates that the color becomes
bluer towards the center, while a value ;SPMgt;1 indicates redder
color towards the center.
The ratio has a simple relation with the
color gradient obtained directly from color profiles. But the
ratio can be used as an indicator of the radial dependence of
color, even when the measured gradient is too noisy to serve the purpose.
Simply on the basis of the conventionally measured color gradients
we could not have been able to make the distinction between radio
and control samples.
Extrapolation of model profiles to inner regions, which are not used in
the fit, provide a measure of star formation activity and dust
absorption there.
One of the objectives of the thesis was to look for signatures of dust in radio galaxies. With the work on scale length ratios we have been able to present a new technique to look for dust as well as star formation. As far as the distribution of dust is concerned, we find that dust is present at the centers of radio galaxies more frequently than in the control sample galaxies. The dust in radio galaxies is seen to be more coherent than in the control sample. We also found that in case of the radio sample, the mass of dust in lanes is correlated to the radio luminosity of the galaxy. The dust mass, however, correlates only weakly with the absolute B magnitude.
According to the Hubble classification scheme, an elliptical
galaxy is totally devoid of dust and gas and possesses no
substructure. Whenever a galaxy was seen to possess a disk, it was
classified as either a lenticular or a spiral. The
bulge and disk parameters obtained by fitting the intensity profile
of each galaxy with a bulge-disk combination indicate that
radio galaxies in our sample have D/B;SPMgt;0.3 and on that
basis alone could be classified as lenticulars or spirals.
To better isolate these disks and other faint features in
the 2-D images, we have adapted the
morphological gradient filter. One of our disky galaxy clearly
shows the presence of spiral-like features. Using the morphological
gradient filter we have been able to bring out spiral-like features
in two more galaxies.