We have presented azimuthally averaged radial brightness profiles and isophotal shapes for 40 M 51-type interacting galaxies in B, V, R and I bands. Also, in order to quantify the characteristics of the bulge and disk components, bulge-disk decompositions were performed. Three of the galaxies, Arp 298 A, Arp 218 A and Kar 203 A, show Freeman type II profiles. This kind of galaxies often have outer rings (Bagget et al. [1998]) which is the case also for the Seyfert galaxy Arp 298 A. On the other hand, Kar 203 A is a peculiar galaxy for which the Freeman type II profile is most probably related to the extremely bright, almost point-like source near to the nucleus.
Most of the galaxies in our sample have typical surface brightness profiles
with a nearly exponential outer disk,
but quite many of them also showed peculiar
characteristics. Namely, six of
the galaxies, Arp 70 A and B, Arp 82 A and B, Arp 87 A and Kar 404 A
had flat brightness profiles outside the normal exponential disks so that
in the flat regions the surface brightnesses were
almost constant between 
= 25-26.5 mag arcsec-2. All
these galaxies belonged to the category of the prototypical
M 51-type pairs where a small companion resides at the very end of the
bridge. The flat profiles appeared prefentially in the main galaxies,
but in two cases also the profiles of the companion galaxies were
flattened. The flat profiles
consisted of 
of all the profiles
studied, and even 
,
if only M 51-type pairs in a more limited sense were considered.
In this kind of pairs the interaction has clearly strongly modified the
galactic disks thus probably
playing an important role in their evolution.
Low surface brightness extensions in the brightness profiles have been
previously reported by Bagget et al. ([1998]) in about 
(18 galaxies) of the galaxies in
their spiral
galaxy sample. The flat profiles found by us are quite different than
for example the profile of the strongly interacting galaxy NGC 3628
which has a sharp outer cutoff just before the flat part of the disk (see
Chromey et al. [1998]). Also, isophotal twists were
detected
in many of the galaxies studied.
We used the profile decomposition method where
fitting to the data was accomplished by minimizing the weighted rms
deviation of
the data from the model profile and where a seeing correction to the
theoretical profiles was applied. Special attention was paid on eliminating the
effects of the nearby galaxies on the brightness profiles. The disks were
well represented by exponential functions in all cases expect for three galaxies
which had Freeman type II profiles. The bulges were
approximately equally well represented both by the R1/4 law
and an exponential function for
of the profiles, while an exponential bulge explained better
of the cases. Only for 
(NGC 5905 and Arp 298 B) a
better fit was obtained by the R1/4 law. Andreakis & Sanders ([1994])
have found for a large sample of normal spiral galaxies that exponential bulges
generally appear in late-type spirals. However, here no clear correlation between the
fitting model and the morphological type of the galaxy was found.
The mean central
surface brightness of the disk in B-band was found to be 21.5 mag arcsec-2,
regardless of the bulge function applied, which is very near to the value of
21.6 mag arcsec-2 originally
obtained by Freeman ([1970]). However, the scatter was large the
central surface brightness varying between 19
and 22.7 mag arcsec-2. This confirms the result by de
Jong ([1996b])
showing that
actually is not a constant, rather there is
only an upper limit for this quantity. We also
found that the weighting function is not an unimportant factor in the
bulge-disk decompositions. It affects mostly the scale lengths so that the
uncertainty in the worst case can be even 20%.
Acknowledgements
We thank the referee Dr. Florence Durret for her valuable comments.
Copyright The European Southern Observatory (ESO)