title: A possible tidal origin of dwarf elliptical galaxies.

abstract:
Dwarf galaxies are often understood as primordial objects that formed within haloes of non-
baryonic dark matter. However, there is theoretical and observational evidence that a second 
generation of galaxies forms through close encounters between primordial galaxies. Galaxies 
from this second generation of galaxies are called tidal dwarf galaxies (TDGs), as they are built 
up from material expelled from the encountering primordial galaxies through the tidal forces that 
acted on them during the encounter. TDGs are quite easy to identify when they are young, but 
not when they are a few Gyr old and the traces of a recent galaxy interaction in their vicinity 
have vanished. Using a large sample of data on early-type galaxies and (young) TDGs, I will 
argue that many, if not most dwarf elliptical galaxies (dEs) and dwarf spheroidal galaxies 
(dSphs) might be ancient TDGs. Since TDGs do not contain an appreciable amount of dark 
matter even if their progenitors did, I will also discuss how the high mass-to-light ratios of many 
dEs and dSphs can be understood if they are ancient TDGs.