THE INTRINSIC SHAPE OF EARLY-TYPE GALAXIES AND THE SCATTER AROUND THEFUNDAMENTAL PLANE

The results of an analysis of the isophotal shapes of 61 galaxies of t he Coma cluster are presented. A modified classification based on isop hotal shape parameters is given and photometric quantities are derived using different fitting techniques. If elliptical galaxies with value s of the isophotal shape parameter a4/a less-than-or-equal-to 0 only a re considered, their scatter around the Fundamental Plane (FP) is redu ced to 10% of the distance for the single object. Galaxies possessing a disk component appear to be shifted from this relation; these deviat ions are correlated with ellipticity. This suggests that projection ef fects and the (unresolved) rotation of the disk components are causing positive shifts from the Fundamental Plane. The effect is also presen t when the D(n) - sigma relation is considered. The observed trend wit h ellipticity is evidence against prolate geometry for elliptical gala xies. Distances of a distant cluster estimated using the FP equation c an be overestimated by up to 14% if the sample of galaxies considered is heavily contaminated by disky galaxies. However, the isophotal shap e analysis can be applied to galaxies as distant as 15000 km/s, provid ing a tool to eliminate this potential problem.