Multicolour photometry of the Shapley 8 cluster of galaxies

Abstract

In a previous paper, we measured 40 redshifts in the core of the rich southern cluster Shapley 8. We now present photographic b26.75 magnitudes, radii and ellipticities, together with |$(u-b)$| and |$(b-r)$| colors for 4903 galaxies within a 4.69 square degree field around this cluster. We have also measured |$(r-i)$| colors for a subset of these galaxies around the cluster core. Our sample is essentially complete to |$b_{26.75}=20.85$|⁠. We discuss the color-related properties of the cluster, together with its luminosity function and spatial distribution. We find a deficit of blue galaxies in the cluster core, implying morphological segregation, and also evidence that the brightest galaxies are less tightly clustered than the rest. There is a clear change of slope at |$M_b \approx -20.4$| in the ultraviolet color–magnitude relations for the E/S0 galaxies. We also show how the color data can be used to isolate high-redshift background galaxies. The mass enclosed within the area we have studied is |$4.5 \times 10^{15}\enspace \text M_\odot$|⁠, which appears to be too low for the Shapley Supercluster to be the explanation of the ‘Great Attractor’.