SDSS-IV/MaNGA: Can impulsive gaseous inflows explain steep oxygen
  abundance profiles \& anomalously-low-metallicity regions?
  Gaseous inflows are necessary suppliers of galaxies' star-forming fuel, but
are difficult to characterize at the survey scale. We use integral-field
spectroscopic measurements of gas-phase metallicity and single-dish radio
measurements of total atomic gas mass to estimate the magnitude and frequency
of gaseous inflows incident on star-forming galaxies. We reveal a mutual
correlation between steep oxygen abundance profiles between $0.25-1.5 R_e$,
increased variability of metallicity between $1.25-1.75 R_e$, and elevated HI
content at fixed total galaxy stellar mass. Employing a simple but intuitive
inflow model, we find that galaxies with total stellar mass less than
$10^{10.1} {\rm M_{\odot}}$ have local oxygen abundance profiles consistent
with reinvigoration by inflows. Approximately 10-25\% of low-mass galaxies
possess signatures of recent accretion, with estimated typical enhancements of
approximately 10-90\% in local gas mass surface density. Higher-mass galaxies
have limited evidence for such inflows. The large diversity of HI mass implies
that inflow-associated gas ought to reside far from the star-forming disk. We
therefore propose that a combination of high HI mass, steep metallicity profile
between $0.25-1.5 R_e$, and wide metallicity distribution function between
$1.25 - 1.75 R_e$ be employed to target possible hosts of inflowing gas for
high-resolution radio follow-up.
