Deep spectroscopy of nearby galaxy clusters: IV The quench of the star
  formation in galaxies in the infall region of Abell\ 85
  Our aim is to understand the role of the environment in the quenching of star
formation of galaxies located in the infall cluster region of Abell 85 (A85).
This is achieved by studying the post-starburst galaxy population as tracer of
recent quenching. By measuring the equivalent width (EW) of the [OII] and
Hdelta spectral lines, we classify the galaxies in three groups: passive (PAS),
emission line (EL), and post-starburst (PSB) galaxies. The PSB galaxy
population represents about 4.5% of the full sample. Dwarf galaxies (Mr >
-18.0) account for about 70 - 80% of PSBs, which indicates that most of the
galaxies undergoing recent quenching are low-mass objects. Independently of the
environment, PSB galaxies are disk-like objects with g - r colour between the
blue ELs and the red PAS ones. The PSB and EL galaxies in low-density
environments show similar luminosities and local galaxy densities. The dynamics
and local galaxy density of the PSB population in high density environments are
shared with PAS galaxies. However, PSB galaxies inside A85 are at shorter
clustercentric radius than PAS and EL ones. The value of the EW(Hdelta) is
larger for those PSBs closer to the cluster centre. We propose two different
physical mechanisms producing PSB galaxies depending on the environment. In low
density environments, gas-rich minor mergers or accretions could produce the
PSB galaxies. For high density environments like A85, PSBs would be produced by
the removal of the gas reservoirs of EL galaxies by ram-pressure stripping when
they pass near to the cluster centre.
