Astron. Astrophys. 323, 317-322 (1997)

5. Conclusion

We have statistically studied the orientation of the SVs of disk galaxies in the Coma cluster. The distribution of polar and azimuthal angles in the supergalactic coordinate system of SVs and the direction of SVs all deviate from the isotropic distribution. We conclude that the distribution of SVs is anisotropic, and this orientation effect is morphologically dependent. There are more S0 galaxies than expected tending to have their SVs parallel to the cluster plane, while the excess orientation of SVs are parallel or perpendicular to the cluster plane for S and Irr galaxies. The excess orientation of the projection on the cluster plane of all disk galaxies are around directions which deviate from the direction pointing to the cluster center by an angle of 30 degrees. Additionally, the projection on the cluster plane of S and Irr galaxies also tend to point to the cluster center. We deduce that the relationship between orientation effect and distance to the cluster or supercluster plane may be a consequence of morphological segregation and SV's morphologically dependent orientation.

Our results show properties of the galaxies which are more characteristic of the "pancake" model for the formation of galaxies than of the other models. However, to explain our results completely, a better theoretical understanding of the collapse process is required, and to check the results obtained here, a larger and deeper sample is necessary.

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

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