The 1D model profile fitting has been done using
points of the surface brightness profile which are further from
the center than 1.5 times the FWHM of the PSF.
This means that we are not using points which are closer to the
center than 
in the fitting.
Having obtained the best fit profiles as
described above, we have extrapolated them
to the center of the galaxy ( 
).
The model profiles for such extrapolation
have been obtained after convolving the best fit model galaxy
with the observed PSF.
The idea behind the extrapolation is to examine the departure of the
inner part of the galaxy from the simple standard model which provides
a good fit beyond the omitted points.
There are three basic possibilities- (1) the inner points
lie on the extrapolation within 
; (2) the inner points
have greater
surface brightness than the extrapolation (we interpret this
as excess emission) and
(3) the inner points have less surface brightness than the extrapolation,
in which case we say that there is absorption.
We have assumed all along that we are dealing with a galaxy that obeys de Vaucouleurs' law and perhaps has an additional exponential disk. However, this assumption need not be true. In that case, some of the effects that we attribute to excess blue emission or star bursts would be upper limits.
Figure 
shows the fits and excess emission for 0446-206.
The extrapolated profile shows hardly any deviation from the observed
profile. A small disk ( 
in both filters)
is seen to be present.
0520-289, shown in Figure is a good example of a galaxy that
exhibits excess emission.
The excess in R exceeds the excess in B indicating the presence
of dust too.
The B-R colormap confirms the presence of dust. An example of dominant dust
absorption is 1103-244, shown in Figure . The absorption
in B exceeds
the absorption in R typical of a dusty galaxy.
We describe the excess related results for the two samples below.
A summary is presented in Table .
of radio galaxies, we find that there is
greater absorption
in B than in R at the center. This is consistent with the presence of
dust in the center, as dust absorption would be greater at shorter
wavelengths. Dust is seen in all but one of these galaxies in
the color
maps that we have discussed above.
Such behavior is seen in 
of the control galaxies. In 3/4th
of these
control galaxies we see the dust in color maps as well.
of the radio galaxies we see greater emission in B
than in R. We cannot say much about the spatial extent of this excess
blue emission, because its angular size is comparable to that of
the PSF. The excess blue emission could be due to
the presence of an AGN which is too
weak, in the optical, for us to have found it in model profile fits.
Only
of the control galaxies have such excess blue emission.
of the radio galaxies, we have excess emission
in B as well as in R. However, the excess in B is less than
the excess in R.
This is easily understood as follows: there is excess blue emission,
as in point 3. But there is also dust, which absorbs
more of the blue light than the R light. The net result is excess
emission in both cases, with less excess in B as observed. In
the control
sample, this behavior is seen in 
of the galaxies. of the radio galaxies we have absorption in B
but emission in R. This can be interpreted as in point 4, with
the effect of dust in the B band dominating the excess in that band.
Some of the excess emission in R manages to get through the dust.
There is no example of this behavior in the control sample.
of the radio galaxies. In the case
of the control sample, we get this behavior in of galaxies.
of radio
galaxies, and in 
of the control galaxies.
We have quantified the excess emission and the absorption due to dust by accumulating the difference between the model galaxy profile and the observed surface brightness profile in the inner region. The procedure carried out is as follows: (1) Obtain a model galaxy profile through a fit to the surface brightness profile as indicated earlier. (2) Along the major axis obtain the difference between the observed profile and the model profile. (3) Starting from the center, at each point add the difference to the sum of the differences at all inner points i.e., obtain a cumulative total of the difference. The excess is then given by the ratio of the cumulative sum to the luminosity of the de Vaucouleurs bulge. Absorption due to dust is indicated by a negative excess.
We present in Figure the fractional cumulative excess for the
two samples in the 
filters upto 
.
These values denote upper limits since
the deviation from which we have calculated the excess could partly be
due to a departure from de Vaucouleurs' law as well.
A numerical comparison is presented in Table .
[Absorption and excess emission for the two samples] Absorption and excess emission details for the radio and control samples.
| B | R | Radio | Control |
| Excess | Excess | 7 | 13 |
| Excess | Deficit | 2 | 2 |
| Deficit | Excess | 10 | 3 |
| Deficit | Deficit | 8 | 12 |
For a galaxy having mass 
, a 
excess
translates to a mass of 
which is large for
a starburst but cannot be ruled out over a period of, say,
.
Our attempt at time-dating the star formation is presented in
Chapter .
The dust extinction will be discussed further in Chapter
where we discuss various issues related to dust.
