On the Origin of Dwarf Elliptical Galaxies: The Fundamental Plane

Early-type dwarf galaxies are the most common type of galaxies observed in the Universe. The origin of this kind of systems is still not well understood. The aim of this paper is to investigate whether the different locations of dwarf galaxies with respect to ellipticals in the face-on view of the fundamental plane could be due to the transformation of bright disc galaxies in low-mass systems by harassment. We have run high-resolution N-body numerical simulations to test the tidal stripping scenario of the dE galaxies. The present simulations modelled several individual tidal stripping events on initial disc-like galaxy models with different bulge-to-disc mass ratios. Tidal stripping is a very efficient mechanism for removing stars and dark matter particles from galaxies. The particles of the disc and halo components were easily stripped, while the bulge not. Thus, the scale length of the discs were 40-50% shorter than the initial ones. Prograde tidal interactions create tidal features like stable bars in the discs of the galaxies. After several tidal interactions the galaxy remnants looks like a dwarf spheroidal system. Simulated galaxies with initial large B/D ratios are closer to the face-on view of the fundamental plane defined by bright E and bulges of early-type galaxies. Nevertheless, galaxies with initial small B/D ratio are located, after four fast tidal encounters, at the position of dE galaxies in the face-on view of the fundamental plane. We conclude that fast galaxy-galaxy interactions are efficient mechanisms for transforming bright galaxies in dwarf ones. Indeed, the different location observed between Es and dEs in the face-on view of the fundamental plane can be explained by the formation of dwarf galaxies by harassment of late-type bright ones.