GASP. XII. The variety of physical processes occurring in a single
  galaxy group in formation
  GAs Stripping Phenomena in galaxies with MUSE (GASP) is a program aimed at
studying gas removal processes in nearby galaxies in different environments. We
present the study of four galaxies that are part of the same group (z= 0.06359)
and highlight the multitude of mechanisms affecting the spatially resolved
properties of the group members. One galaxy is passive and shows a regular
stellar kinematics. The analysis of its star formation history indicates that
the quenching process lasted for a few Gyr and that the star formation declined
throughout the disk in a similar way, consistent with strangulation. Another
galaxy is characterised by a two-component stellar disk with an extended gas
disk that formed a few 10^8 yr ago, most likely as a consequence of gas
accretion. The third member is a spiral galaxy at the edges of the group, but
embedded in a filament. We hypothesise that the compression exerted by the
sparse intergalactic medium on the dense circumgalactic gas switches on star
formation in a number of clouds surrounding the galaxy ("cosmic web
enhancement"). Alternatively, also ram pressure stripping might be effective.
Finally, the fourth galaxy is a spiral with a truncated ionised gas disk and an
undisturbed stellar kinematics. An analytical model of the galaxy's restoring
pressure, and its location and velocity within the cluster, suggest ram
pressure is the most likely physical mechanism in action. This is the first
optical evidence for stripping in groups.
