We investigate two possible effects of the tidal field induced by a spherical
cluster on its elliptical galaxy members: the modification of the ellipticity
of a spherical galaxy and the isophotal alignment in the cluster radial
direction of a misaligned prolate galaxy. Numerical N-body simulations have
been performed for radial and circular galactic orbits. The properties of the
stars' zero--velocity surfaces in the perturbed galaxies are explored briefly,
and the adiabaticity of the galaxy to the external field is discussed. For a
choice of parameters characteristic of rich clusters we find that the induced
ellipticity on a spherical galaxy is below or close to the detectability level.
But we find that the tidal torque can result in significant isophotal alignment
of the galaxies' major axis with the cluster radial direction if the galaxy is
outside the cluster core radius. The time required for the alignment is very
short compared with the Hubble time. A significant increase in the ellipticity
of the outer isophotes of the prolate model is also found, but with no
observable isophotal twisting. Our main prediction is an alignment segregation
of the elliptical galaxy population according to whether their orbits lie
mostly outside or inside the cluster core radius. These results also suggest
that galactic alignment in rich clusters is not incompatible with a bottom-up
galaxy formation scenario.Comment: 20 pages, uuencoded compressed tarred postscrip
