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Decoupled gas kinematics in isolated S0 galaxies

A sample of completely isolated S0 galaxies has been studied by means of long-slit spectroscopy at the Russian 6-m telescope. 7 of 12 galaxies have revealed a presence of extended ionized-gas discs which rotation is mostly decoupled from the stellar kinematics: 5 of 7 (71+/-17%) galaxies show a visible counterrotation of the ionized-gas component with respect to the stellar component. The emission-line diagnostics demonstrates a wide range of the gas excitation mechanisms, although a pure excitation by young stars is rare. We conclude that in all cases the extended gaseous discs in our sample S0s are of external origin, despite the visible isolation of the galaxies. Possible sources of external accretion, such as systems of dwarf gas-rich satellites or cosmological cold-gas filaments, are discussed.