In Chapter 
we have explained the procedure
we follow to decompose the surface brightness profile of a galaxy
into de Vaucouleurs bulge (B) and an exponential disk (D) component.
The ratio of the
luminosities of the two components, D/B, is the factor that
indicates the presence of a disk. In Figure we show the
typical D/B values for galaxies of different morphological types
(Kent, 1985).
As per Hubble's original
classification scheme (Hubble, 1926), elliptical galaxies do
not have any structure. Whenever a disk like component was suspected
the galaxy was labeled S0. Recent studies have shown, however,
that elliptical galaxies can also be disky. It is likely that
such galaxies may be the lower end, in diskiness, of S0 galaxies.
In Figure we show the distribution of the D/B ratio
for the radio and control samples. For the R filter we also depict the
distribution as a histogram for both the samples in Figure .
It is seen that in general the D/B values in both the filters are similar.
Several galaxies in the radio as well as control samples,
have a D/B;SPMlt;0.1. These are likely to be insignificant
disks possibly arising from deviation form the 
law or a weak
point source (when 
is also small).
We notice that there are a few galaxies with a D/B;SPMgt;0.3 in both
the filters. In this section we consider these galaxies. The
value of D/B;SPMgt;0.3 was chosen so that even if the scatter around the
D/B values of different galaxy types plotted in Figure
is taken into consideration, the galaxies with these values will
not be elliptical.
In the radio sample, there are five such galaxies, while in the control
sample there are four galaxies with this lower limit for the ratio.
There is also a class of objects for which D/B;SPMgt;0.3 but such that
FWHM of the PSF. Such cases are likely to be the result of a genuine
departure from de Vaucouleurs' law near the center or indicative of the presence
of a weak AGN. We do not consider these galaxies to be disky in the
normal sense of the word and have not treated them as being significant
in the following discussion.
We present here results on 5 radio galaxies with prominent disks. We
examine the host galaxy properties and the radio structure. 4 of the 5
galaxies have FR II morphology and even the fifth one is of type FR II?.
The D/B
ratio is suggestive of spiral galaxies. However, we do not see
spiral arms except in one case.
Relevant parameters for these galaxies are listed in Table .
and
. The radio source is of type FR II.
The morphology in the two filters shows
a bar like structure along with a linear structure at right angle to
the 'bar', arising from one end of the bar. There are also
other flocculent structures present.
D/B values are consistent with the galaxy being an Sb. The
disk scale length is in this case a few times the FWHM of the PSF,
but only a fraction of the bulge scale length. We are therefore
again detecting a small disk relative to the bulge.
and 
. The ellipticity
of this galaxy changes from 0.1 near the center to 0.4 in the outer
region. There is a spiral galaxy 15'' away with which the radio
galaxy is likely to
be interacting. The D/B values in
both filters are ;SPMgt;4. From this, and the disk and bulge scale
lengths, the galaxy can be classified as Sc.
This is the most
likely candidate from our radio sample to be a normal spiral
as defined by bulge and disk parameters.
No spiral structure is seen.
and 
.
The galaxy is flattened
near the center ( 
near the center compared to
on the outskirts). It has a bluer center and an
armlike extension is seen along the radio axis.
The K' image does not show the armlike structure and hence it is
likely to be the outcome of recent star forming activity.
This galaxy has large D/B (;SPMgt;5) in both filters
and on that
basis alone would be classified as Sc. However the disk scale length
is comparable to the FWHM of the PSF. It is also much smaller
than 
in the R filter. In the B filter, and are
comparable in size. However, the smaller bulge scale length in this
filter, relative to in the R filter, is suspected to be a
result of excess blue emission in the central region. Taking all
this into account, we conclude that the profile fit has detected a
small scale disk-like structure. The linear scale length of this
structure in R is 
, and it is much smaller than
the bulge scale length of 
. The ratio of the disk to
bulge scale lengths is therefore much smaller than is observed for
standard disk galaxies.
radio flux 
and has a radio
luminosity of 
. The radio source
is of type FR II.
This galaxy has a 
, which is large enough
for it to be classified
as an Sb spiral. However 
is
considerably smaller. This difference in parameter values is also
seen in , as well as in bulge parameters. Due to the
difference in values from one filter to another,
it is not possible to confidently classify the galaxy. The differences
are caused by the presence of dust as well as blue emission, which are
seen in the color maps and profile fits. We show the galaxy in
Figure .
and 
.
D/B values in 
are consistent with SA classification. in 
is comparable
to the FWHM of the PSF.
We describe here objects from the control sample that have
D/B;SPMgt;0.3 in both filters. The control galaxies have been chosen to be
of early type and we expect a few S0s but no spiral galaxies. Relevant
parameters for the 4 disky galaxies are given in Table .
.
The D/B in
B is consistent with a lenticular and D/B in R
consistent with a SA.
