The fundamental plane of isolated early-type galaxies

Here we present new measurements of effective radii, surface brightnesses and internal velocity dispersions for 23 isolated early-type galaxies. The photometric properties are derived from new multicolour imaging of ten galaxies, whereas the central kinematics for seven galaxies are taken from forthcoming work by Hau & Forbes. These are supplemented with data from the literature. We reproduce the colour-magnitude and Kormendy relations and strengthen the result of the recent work of Reda et al. that isolated galaxies follow the same photometric relations as galaxies in high-density environments. We also find that some isolated galaxies reveal fine structure indicative of a recent merger, while others appear undisturbed. We examine the Fundamental Plane both in the traditional R-e, mu(e), sigma space and also in kappa space. Most isolated galaxies follow the same Fundamental Plane tilt and scatter for galaxies in high-density environments. However, a few galaxies notably deviate from the Plane in the sense of having smaller M/L ratios. This can be understood in terms of their younger stellar populations, which are presumably induced by a gaseous merger. Overall, isolated galaxies have similar properties to those in groups and clusters with a slight enhancement in the frequency of recent mergers/interactions.