Flaming, bright galaxies along the filaments of A 2744

• Published in: Astronomy and astrophysics (Berlin) 2007-08, Vol.470 (2), p.425-429
• Main Authors: Braglia, F., Pierini, D., Böhringer, H.
• Format: Article
• Language: English
• Subjects: Astronomy; cosmology: observations; Earth, ocean, space; Exact sciences and technology; galaxies: clusters: general; galaxies: clusters: individual: Abell 2744; galaxies: clusters: individual: AC 118; galaxies: evolution; galaxies: interactions
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:20077257

Context.The existence of a lumpy, large-scale filamentary structure is at the basis of the current paradigm of cosmic formation and evolution of clusters. The star-formation history of galaxies falling into a cluster is altered as a result of the environmental stresses. Aims.We investigate the relation between substructure and properties of the galaxy population in a $30^{\prime} \times 30^{\prime}$ region centred on the massive merging cluster A 2744 at z ~ 0.3. Methods.Multi-object spectroscopy at low resolution and BVR photometry are used to detect the presence of substructure through a Dressler-Schectman analysis and the photometric redshift technique, respectively. Galaxies at the same photometric redshift of the cluster are divided into red and blue according to their distribution in the $B-R$ vs. R colour–magnitude diagram. Results.We identify two large-scale filaments associated with A 2744. Along these filaments, the blue-to-red galaxy number ratio increases together with the cluster-centric distance but peaks slightly beyond the cluster virial radius. The filaments host a population of bright, large (i.e. more luminous than $R^{\star}$ for the main body of the cluster and with angular sizes of 13–22 $h_{\rm 70}^{\rm-1}$ kpc) blue galaxies that is hardly found among galaxies lying in a neighbouring low-density environment at the same redshift of the cluster. Conclusions.These results can be interpreted as a manifestation of galaxy harassment.