The diverse evolutionary pathways of post-starburst galaxies
  About 35 years ago a class of galaxies with unusually strong Balmer
absorption lines and weak emission lines was discovered in distant galaxy
clusters. These objects, alternatively referred to as post-starburst, E+A or
k+a galaxies, are now known to occur in all environments and at all redshifts,
with many exhibiting compact morphologies and low-surface brightness features
indicative of past galaxy mergers. They are commonly thought to represent
galaxies that are transitioning from blue to red sequence, making them critical
to our understanding of the origins of galaxy bimodality. However, recent
observational studies have questioned this simple interpretation. From
observations alone, it is challenging to disentangle the different mechanisms
that lead to the quenching of star formation in galaxies. Here we present
examples of three different evolutionary pathways that lead to galaxies with
strong Balmer absorption lines in the EAGLE simulation: classical blue-to-red
quenching, blue-to-blue cycle and red-to-red rejuvenation. The first two are
found in both post-starburst galaxies and galaxies with truncated star
formation. Each pathway is consistent with scenarios hypothesised for
observational samples. The fact that 'post-starburst' signatures can be
attained via various evolutionary channels explains the diversity of observed
properties, and lends support to the idea that slower quenching channels are
important at low redshift.
