  Using spatially resolved spectroscopy from SDSS-IV MaNGA we have demonstrated
that low ionisation emission line regions (LIERs) in local galaxies result from
photoionisation by hot evolved stars, not active galactic nuclei. LIERs are
ubiquitous in both quiescent galaxies and in the central regions of galaxies
where star formation takes place at larger radii. We refer to these two classes
of galaxies as extended LIER (eLIER) and central LIER (cLIER) galaxies
respectively. cLIERs are late type galaxies located around the green valley, in
the transition region between the star formation main sequence and quiescent
galaxies. These galaxies display regular disc rotation in both stars and gas,
although featuring a higher central stellar velocity dispersion than star
forming galaxies of the same mass. cLIERs are consistent with being slowly
quenched inside-out; the transformation is associated with massive bulges,
pointing towards the importance of bulge growth via secular evolution. eLIERs
are morphologically early types and are indistinguishable from passive galaxies
devoid of line emission in terms of their stellar populations, morphology and
central stellar velocity dispersion. Ionised gas in eLIERs shows both disturbed
and disc-like kinematics. When a large-scale flow/rotation is observed in the
gas, it is often misaligned relative to the stellar component. These features
indicate that eLIERs are passive galaxies harbouring a residual cold gas
component, acquired mostly via external accretion. Importantly, quiescent
galaxies devoid of line emission reside in denser environments and have
significantly higher satellite fraction than eLIERs. Environmental effects thus
represent the likely cause for the existence of line-less galaxies on the red
sequence.
