SIMBAD references

Lenticular galaxies are a morphological class of disc galaxies that in general lacks current star formation and extended gaseous discs. However recent ultraviolet (UV) surveys have revealed extended UV discs and rings even among these `red and dead' galaxies, and their origin is now still unclear. We have studied the nature of the outer star-forming, UV-detected rings in four unbarred S0 galaxies by undertaking their long-slit spectroscopy with the focal reducer SCORPIO of the Russian 6-m telescope. Gaseous discs in NGC 252 and in NGC 4513 have decoupled kinematics, and the ionized gas of their rings is certainly excited by young stars. Just these two galaxies belong to galaxy groups. Two other, quite isolated S0 galaxies with the UV rings, IC 522 and NGC 446, demonstrate the shock-dominated gas excitation in the UV-detected rings, so their rings may probably have impact origin. However, in all four galaxies the ionized gas reveals the oxygen abundance close to the solar one, so the hypothesis of gas accretion from cosmological filaments seems to be unfavourable. Rather another large galaxy may be a donor of outer gas in the galaxies of our sample.