GASP XXIV. The history of abruptly quenched galaxies in clusters
  The study of cluster post starburst galaxies gives useful insights on the
physical processes quenching the star formation in the most massive
environments. Exploiting the MUSE data of the GAs Stripping Phenomena in
galaxies (GASP) project, we characterise the quenching history of 8 local
cluster galaxies that were selected for not showing emission lines in their
fiber spectra. We inspect the integrated colors, the Hb rest frame equivalent
widths (EW), star formation histories (SFHs) and luminosity-weighted age (LWA)
maps finding no signs of current star formation throughout the disks of these
early-spiral/S0 galaxies. All of them have been passive for at least 20 Myr,
but their SF declined on different timescales. In most of them the outskirts
reached undetectable SFRs before the inner regions (outside-in quenching). Our
sample includes three post-starforming galaxies, two passive galaxies and three
galaxies with intermediate properties. The first population shows blue colors,
deep Hb in absorption (EW>>2.8A), young ages (8.8<log(LW [yr])<9.2). Two of
these galaxies show signs of a central SF enhancement before quenching. Passive
galaxies have instead red colors, EW(Hb)<2.8A, ages in the range
9.2<log(LWA[yr])<10. Finally, the other galaxies are most likely in transition
between a post starforming and passive phase, as they quenched in an
intermediate epoch and have not lost all the star forming features yet. The
outside-in quenching, the morphology and kinematics of the stellar component,
along with the position of these galaxies within massive clusters
(sigma_cl=550-950km/s) point to a scenario in which ram pressure stripping has
removed the gas, leading to quenching. Only the three most massive galaxies
might alternatively have entered the clusters already quenched. These galaxies
are therefore at the final stage of the rapid evolution galaxies undergo when
they enter the clusters.
