  While we observe a large amount of cold interstellar gas and dust in a subset
of the early-type galaxy (ETG) population, the source of this material remains
unclear. The two main, competing scenarios are external accretion of lower
mass, gas-rich dwarfs and internal production from stellar mass loss and/or
cooling from the hot interstellar medium (ISM). We test these hypotheses with
measurements of the stellar and nebular metallicities of three ETGs (NGC 2768,
NGC 3245, and NGC 4694) from new long-slit, high signal-to-noise ratio
spectroscopy from the Multi-Object Double Spectographs (MODs) on the Large
Binocular Telescope (LBT). These ETGs have modest star formation rates and
minimal evidence of nuclear activity. We model the stellar continuum to derive
chemical abundances and measure gas-phase abundances with standard nebular
diagnostics. We find that the stellar and gas-phase abundances are very
similar, which supports internal production and is very inconsistent with the
accretion of smaller, lower metallicity dwarfs. All three of these galaxies are
also consistent with an extrapolation of the mass-metallicity relation to
higher mass galaxies with lower specific star formation rates. The emission
line flux ratios along the long-slit, as well as global line ratios clearly
indicate that photoionization dominates and ionization by alternate sources
including AGN activity, shocks, cosmic rays, dissipative magnetohydrodynamic
waves, and single degenerate Type Ia supernovae progenitors do not
significantly affect the line ratios.
