The evolution of the mass-metallicity relation in SDSS galaxies
  uncovered by astropaleontology
  We have obtained the mass-metallicity (M-Z) relation at different lookback
times for the same set of galaxies from the Sloan Digital Sky Survey, using the
stellar metallicities estimated with our spectral synthesis code STARLIGHT. We
have found that this relation steepens and spans a wider range in both mass and
metallicity at higher redshifts. We have modeled the time evolution of stellar
metallicity with a closed-box chemical evolution model, for galaxies of
different types and masses. Our results suggest that the M-Z relation for
galaxies with present-day stellar masses down to 10^10 M_sun is mainly driven
by the history of star formation history and not by inflows or outflows.
