  Early type galaxies (ETGs) frequently show emission from warm ionized gas.
These Low Ionization Emission Regions (LIERs) were originally attributed to a
central, low-luminosity active galactic nuclei. However, the recent discovery
of spatially-extended LIER emission suggests ionization by both a central
source and an extended component that follows a stellar-like radial
distribution. For passively-evolving galaxies with old stellar populations, hot
post-Asymptotic Giant Branch (AGB) stars are the only viable extended source of
ionizing photons. In this work, we present the first prediction of LIER-like
emission from post-AGB stars that is based on fully self-consistent stellar
evolution and photoionization models. We show that models where post-AGB stars
are the dominant source of ionizing photons reproduce the nebular emission
signatures observed in ETGs, including LIER-like emission line ratios in
standard optical diagnostic diagrams and H$\alpha$ equivalent widths of order
0.1-3 angstroms. We test the sensitivity of LIER-like emission to the details
of post-AGB models, including the mass loss efficiency and convective mixing
efficiency, and show that line strengths are relatively insensitive to post-AGB
timescale variations. Finally, we examine the UV-optical colors of the models
and the stellar populations responsible for the UV-excess observed in some
ETGs. We find that allowing as little as 3% of the HB population to be
uniformly distributed to very hot temperatures (30,000 K) produces realistic UV
colors for old, quiescent ETGs.
