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

Abstract

Context: Clusters of galaxies host a diffuse population of intergalactic stars. Diffuse optical light is observed in clusters up to redshift z ∼ 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 ∼ 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^-2 (observed frame) around a total of seven BCGs, extending up to galactocentric distances of 100 h₇₀^-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.