Multi-wavelength study of X-ray luminous clusters at z ~ 0.3 I. Star
  formation activity of cluster galaxies
  The current paradigm of cosmic formation and evolution of galaxy clusters
foresees growth mostly through merging. Galaxies in the infall region or in the
core of a cluster undergo transformations owing to different environmental
stresses. For two X-ray luminous clusters at redshift z ~ 0.3 with opposite
X-ray morphologies, RXCJ0014.3-3022 and RXCJ2308.3-0211, we assess differences
in galaxy populations as a function of cluster topography. Cluster large-scale
structure and substructure are determined from the combined photometry in the
B, V, and R bands, and from multi-object optical spectroscopy at low
resolution. A spectral index analysis is performed, based on the [OII] and
Hdelta features, and the D4000 break, available for more than 100 member
galaxies per cluster. Combination of spectral indices and FUV-optical colours
provides a picture of the star formation history in galaxies. In spite of the
potential presence of a small fraction of galaxies with obscured star formation
activity, the average star-formation history of cluster members is found to
depend on cluster-centric distance and on substructure. There is a sharp
increase in star formation activity along two well-defined filamentary
structures of the merging cluster RXCJ0014.3-3022, out to its virial radius and
beyond, produced by luminous (L ~ L*) and sub-L* galaxies. Conversely, the
regular cool-core cluster RXCJ2308.3-0211 mostly hosts galaxies which either
populate the red sequence or are becoming passive. These results suggest the
existence of a correspondence between assembly state and overall age of the
stellar populations of galaxies inside the virialized region and in the
surrounding large scale structure of massive clusters at z ~ 0.3. (Abridged)
