Galaxy gas flows inferred from a detailed, spatially resolved metal
  budget
  We use the most extensive integral field spectroscopic map of a local galaxy,
NGC 628, combined with gas and stellar mass surface density maps, to study the
distribution of metals in this galaxy out to 3 effective radii ($\rm R_e$). At
each galactocentric distance, we compute the metal budget and thus constrain
the mass of metals lost. We find that in the disc about 50% of the metals have
been lost throughout the lifetime of the galaxy. The fraction of metals lost is
higher in the bulge ($\sim$70%) and decreases towards the outer disc ($\rm \sim
3 \ R_e$). In contrast to studies based on the gas kinematics, which are only
sensitive to ongoing outflow events, our metal budget analysis enables us to
infer the average outflow rate during the galaxy lifetime. By using simple
physically motivated models of chemical evolution we can fit the observed metal
budget at most radii with an average outflow loading factor of order unity,
thus clearly demonstrating the importance of outflows in the evolution of disc
galaxies of this mass range ($\rm log(M_\star/M_\odot) \sim 10)$. The observed
gas phase metallicity is higher than expected from the metal budget and
suggests late-time accretion of enriched gas, likely raining onto the disc from
the metal-enriched halo.
