SDSS-IV MaNGA: When is morphology imprinted on galaxies?
  It remains an open question as to how long ago the morphology that we see in
a present-day galaxy was typically imprinted. Studies of galaxy populations at
different redshifts reveal that the balance of morphologies has changed over
time, but such snapshots cannot uncover the typical timescales over which
individual galaxies undergo morphological transformation, nor which are the
progenitors of today's galaxies of different types. However, these studies also
show a strong link between morphology and star-formation rate over a large
range in redshift, which offers an alternative probe of morphological
transformation. We therefore derive the evolution in star-formation rate and
stellar mass of a sample of 4342 galaxies in the SDSS-IV MaNGA survey through a
stellar population "fossil record" approach, and show that the average
evolution of the population shows good agreement with known behaviour from
previous studies. Although the correlation between a galaxy's contemporaneous
morphology and star-formation rate is strong over a large range of lookback
times, we find that a galaxy's present-day morphology only correlates with its
relatively recent (~2 Gyr) star-formation history. We therefore find strong
evidence that morphological transitions to galaxies' current appearance
occurred on timescales as short as a few billion years.
