Clues on the rejuvenation of the S0 galaxy NGC 404 from the chemical
  abundance of its outer disk
  The oxygen abundance of the outer disk of the nearby S0 galaxy NGC 404, a
prototypical early-type galaxy with extended star formation, has been derived
from the analysis of HII region spectra. The high mean value found,
12+log(O/H)=8.6 \pm 0.1, equivalent to approximately 80% of the solar value,
argues against both the previously proposed cold accretion and recent merger
scenarios as viable mechanisms for the assembly of the star-forming gas. The
combination of the present-day gas metallicity with the published star
formation history of this galaxy favors a model in which the recent star
forming activity represents the declining tail of the original one.
