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 Re, μe, σ space and also in κ 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.