Structural properties of isolated early-type galaxies. The dependence of scaling relations on environment

Aims. In order to investigate whether gravitational interactions between galaxies are able to modify their structural properties, we determine the Kormendy relation (KR) for a sample of isolated early-type galaxies (ETG) for which we have measured several photometric parameters. This relation is compared with that obtained for a sample of ETG of the Coma Cluster, and with that obtained for a sample of perturbed S0 galaxies contained within high-density environments. Methods. Using very strict physical isolation criteria we selected a sample of 82 E and S0 galaxies from the CfA catalogue, in the redshift range 5000 km s(-1) <= cz < 10 000 km s(-1). We obtained the photometric parameters, ( re, < S Be >) and total magnitude for 21 galaxies in the B filter and for 23 in the Gunn r filter. Results. The main result we obtained is that the KR is the same for isolated galaxies and for galaxies in high- density environments or in interaction. In addition we found evidence that the intrinsic dispersion of the KR depends on the magnitude range within which the galaxies are contained (larger dispersion for larger magnitude range), and not on the degree of gravitational interaction to which these galaxies are subjected.