Local and global gas metallicity versus stellar age relation in MaNGA
  galaxies
  The search for new global scaling relations linking physical properties of
galaxies has a fundamental interest. Furthermore, their recovery from spatially
resolved relations has been one of the spotlights of integral field
spectroscopy (IFS). In this study we investigate the existence of global and
local relations between stellar age ($Age_\star$) and gas-phase metallicity
($Z_g$). To this aim, we analyze IFS data for a sample of 736 star-forming disk
galaxies from the MaNGA survey. We report a positive correlation between the
global $Z_g$ and $D(4000)$ (an indicator of stellar age), with a slope that
decreases with increasing galaxy mass. Locally, a similar trend is found when
analyzing the $Z_g$ and $D(4000)$ of the star-forming regions, as well as the
residuals resulting from removing the radial gradients of both parameters. The
local laws have systematically smaller slopes than the global one. We ascribe
this difference to random errors, that make the true slope of the
$Age_\star-Z_g$ relation to be systematically underestimated when performing a
least square fitting. The explored relation is intimately linked with the
already known relation between gas metallicity and star formation rate at fixed
mass, both presenting a common physical origin.
