Diffuse stellar emission in X-ray luminous galaxy clusters at z similar to 0.3 I. Is the diffuse optical light boosted and rejuvenated in merging clusters?

Context. Clusters of galaxies host a diffuse population of intergalactic stars. Diffuse optical light is observed in clusters up to redshift z sim 0.4. Recent cosmological hydrodynamical simulations show that this intracluster light originates nearly in parallel with the build-up of the brightest cluster galaxy (BCG), as identified at z =0. However, theory proposes alternative scenarios for its origin. Aims. We searched for diffuse stellar emission around BCGs in three of the most X-ray luminous clusters found at z sim 0.3 in the REFLEX cluster survey and observed with XMM-Newton . These systems (RXC J0014.3-3022, RXC J0232.2-4420, and RXC J2308.3-0211) are in different dynamical states, as witnessed by their X-ray morphology and optical appearence (e.g. multiplicity of BCGs). Methods. Existing medium-deep, wide-field imaging in B and R bands allows extension, intensity, and colour of the stellar emission to be determined across a region that encompasses the X-ray emission from the intracluster medium (ICM) in each cluster. Results. Diffuse stellar emission is robustly detected down to a surface brightness of 26 R-mag arcsec super(-2) (observed frame) around a total of seven BCGs, extending up to galactocentric distances of similar to 100 h sub(70) super(-1) kpc. In particular, it surrounds a pair of BCGs in RXC J0232.2-4420, while it bridges two BCGs associated with the minor subcomponent of the merging cluster RXC J0014.3-3022. The diffuse light detected at the greatest distances from the BCGs of the rather regular clusters RXC J0232.2-4420 and RXC J2308.3-0211 follows the ICM distribution. Its B-R colour is consistent with the colours measured within the BCG effective radii. The diffuse light around the two pairs of BCGs in RXC J0014.3-3022 exhibits bluer colours than the BCG central regions by up to 0.5 mag. Conclusions. If the contribution of the intracluster light (ICL) to the detected diffuse light around BCGs is not negligible, ICL and BCGs have similar stellar populations in relatively relaxed clusters. Merging on a cluster scale eventually adds gravitational stresses to BCGs and other galaxies in subcluster cores. This event may affect the properties of the diffuse stellar emission around BCGs. Shredding of star-forming, low-metallicity dwarf galaxies is favoured as the cause of the bluer B-R colours of the diffuse stellar component around the two pairs of BCGs in the merging cluster RXC J0014.3-3022.