Fast and slow paths to quiescence: ages and sizes of 400 quiescent
  galaxies from the LEGA-C survey
  We analyze stellar age indicators (D$_n$4000 and EW(H$\delta$)) and sizes of
467 quiescent galaxies with $M_\ast \geq 10^{10} M_\odot$ at $z\sim0.7$ drawn
from DR2 of the LEGA-C survey. Interpreting index variations in terms of
equivalent single stellar population age, we find that the median stellar
population is younger for larger galaxies at fixed stellar mass. The effect is
significant, yet small; the ages of the larger and the smaller subsets differ
by only $<500$ Myr, much less than the age variation among individual galaxies
($\sim1.5$ Gyr). At the same time, quiescent galaxies with the strongest
H$\delta$ absorption --- those experienced recent and rapid quenching events
--- tend to be smaller than the average. These co-existing trends unify
seemingly contradictory results in the literature; the complex correlations
between size and age indicators revealed by our large sample of galaxies with
high-quality spectra suggest that there are multiple evolutionary pathways to
quiescence. Regardless of the specific physical mechanisms responsible for the
cessation of star formation in massive galaxies, the large scatter in D$_n$4000
and EW(H$\delta$) immediately implies that galaxies follow a large variety in
evolutionary pathways. On the one hand, we see evidence for a process that
slowly shuts off star-formation and transforms star-forming galaxies to
quiescent galaxies without necessarily changing their structures. On the other
hand, there is likely a mechanism that rapidly quenches galaxies, an event that
coincides with dramatic structural changes, producing small post-starburst
galaxies.
