Bulges on the Fundamental Plane of early-type galaxies

In an ongoing effort to study the formation and evolution of galactic bulges, we have investigated the position of 19 bulges of type S0-Sbc on the Fundamental Plane (FP). We find that bulges, in both B and K band, lie close to but slightly below the FP defined by ellipticals and S0s, i.e. are slightly brighter. There are hints that bulges of later morphological type are situated below the other bulges in our sample. The FP results are consistent with the picture, obtained from our recent analysis of HST colours, that bulges are old, except for the Sbc galaxies. The fact that bulges lie so close to the FP of ellipticals and S0s implies that their formation epoch must have been similar to, at most about 2.5 Gyr earlier than, cluster Es and S0s, and that the surrounding disc does not significantly affect their structure.