The Substructure in the Cluster Abell85

Extract

We revisit the complex structure of the A85-A87 cluster, based on a volume complete VLA-HI imaging survey, as well as optical photometry and spectroscopy. HI imaging studies of a few nearby clusters have shown that most of the HI rich galaxies around clusters are located within infalling groups. The case of A 85 is a very peculiar one, with all the 11 HI-detected galaxies projected east of A 85, and all but one with much lower radial velocities (~ 15,000 km s⁻¹ than the cluster's systemic velocity (16,500 km s⁻¹) In order to quantify the degree of substructure in A 85 we estimate the parameter δ defined by Dressler and Schectman, and plot it in Fig. 1a: many large circles in the same area indicate a great possibility of substructuring (Bravo-Alfaro et al. 2007 in prep).