8 Conclusions

We present a homogenous catalogue of 660 galaxies brighter than B₂₅=19.5 in the central 10 square degrees area of the Perseus cluster based on a Schmidt plate survey. The catalogue provides accurate positions, B₂₅ magnitudes, position angles and major and minor axis of the $\mu_B=25$magarcsec^-2 isophote. Furthermore, morphological information is given, derived mainly from deep images obtained from the co-addition of a large number of digitised Schmidt plates. Cross-identifications and radial velocities are also listed if available. The galaxy catalogue is expected to be complete to $B_{25}\approx18$. Background contamination may be important for B₂₅>18 but should be negligible for B₂₅<17.

We find a total fraction of about 50% spiral galaxies if we consider the whole field. On the other hand, the galaxies in the inner part () of the cluster are strongly dominated by types E and S0. In this context, we note that the BGP galaxy sample, used in several previous studies of the Perseus cluster, is limited to the central 30' and is biased, therefore, towards E and S0 types. For example, KS83 studied the BGP sample and found a significant spiral under-abundance in the Perseus cluster.

The investigation of the projected distribution of the different morphological types yields a strong radial segregation, density segregation, and segregation due to a privileged direction in the distribution of E+S0 galaxies. All detected segregations are statistically significant. In agreement with Andreon (1994) we conclude that the Perseus cluster is not in a virialized state. The privileged direction is aligned with the elongation of the X-ray contours. In the region of the eastern X-ray excess (e.g., Ettori et al. [1998]), we find a significantly higher fraction of spiral and irregular galaxies compared with the morphological mix of the galaxies on the opposite side of the X-ray centre.

We detected a conspicuous clump in the projected distribution of the fainter (B>16) galaxies at $\alpha ({J}2000.0) = 3^{\rm h}20\hbox{$.\!\!^{\rm m}$}4$, $\delta ({J}2000.0) = 43\hbox{$^\circ$}4'$, i.e. about $1.5\hbox{$^\circ$}$ north of the cluster centre, which is shown to be not a substructure of A426. Radial velocities obtained for three galaxies of that clump indicate the presence of a background cluster at z=0.050. Owing to a probably patchy foreground extinction over the field we have not investigated other substructures in the projected galaxy distribution.

It seems not possible to define a unique centre for the projected galaxy distribution. Different cluster centres have been found for S+Irr galaxies, on the one hand, and E+S0, on the other hand, reflecting a morphological segregation. Moreover, the optical cluster centre position significantly depends on the considered sky area. In no case, however, the optical centre position is in coincidence with the X-ray centre.

We have studied the galaxy alignments by means of extensive statistical tests. The results show that there are no significant preferred directions in the distribution of the orientation angles PA.

The LFs for different morphological types clearly differ from each other. The type-dependent LFs show several properties in agreement with universal type-dependent LFs predicted by Andreon ([1998b]). On the other hand, there are remarkable differences. In particular, the spiral LF is rather steep and the S0 LF shows no pronounced maximum. The total B-band luminosity of A426 is estimated to $L_{B, {\rm tot}}=(6.5\pm0.9)\times10^{12}\,L_{B, \odot} \times h_{50}^{-2}$.

Acknowledgements

We thank the anonymous referee for constructive comments and suggestions. J.B. acknowledges financial support from the Deutsche Forschungsgemeinschaft under grant ME1350/3. This research has been made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.