The Shapes of BCGs and normal Ellipticals in Nearby Clusters
  We compare the apparent axial ratio distributions of Brightest Cluster
Galaxies (BCGs) and normal ellipticals (Es) in our sample of 75 galaxy clusters
from the WINGS survey. Most BCGs in our clusters (69%) are classified as cD
galaxies. The sample of cDs has been completed by 14 additional cDs (non-BCGs)
we found in our clusters. We find that: (i) Es have triaxial shape, the
triaxiality sharing almost evenly the intrinsic axial ratios parameter space,
with a weak preference for prolateness; (ii) the BCGs have triaxial shape as
well. However, their tendence towards prolateness is much stronger than in the
case of Es. Such a strong prolateness appears entirely due to the sizeable
(dominant) component of cDs inside the WINGS sample of BCGs. In fact, while the
'normal'(non-cD) BCGs do not differ from Es, as far as the shape distribution
is concerned, the axial ratio distribution of BCG_cD galaxies is found to
support quite prolate shapes; (iii) our result turns out to be strongly at
variance with the only similar, previous analysis by Ryden et al.(1993)(RLP93),
where BCGs and Es were found to share the same axial ratio distribution; (iv)
our data suggest that the above discrepancy is mainly caused by the different
criteria that RLP93 and ourselves use to select the cluster samples, coupled
with a preference of cDs to reside in powerful X-ray emitting clusters; (v) the
GIF2 N-body results suggest that the prolateness of the BCGs (in particular the
cDs) could reflect the shape of the associated dark matter halos.
