Angular distribution of satellite galaxies from the Sloan Digital Sky   Survey Data Release 4
  We explore the angular distribution of two samples of satellite galaxies orbiting isolated hosts extracted from the Sloan Digital Sky Survey Data Release 4. We find a clear alignment of the satellites along the major axis of their hosts when restricting the analysis to red hosts. The anisotropy is most pronounced for red satellites of red hosts. We find that the distribution of the satellites about blue, isolated hosts is consistent with isotropy. We show that under the assumption that the true, underlying distribution of satellites of blue hosts exhibits the same anisotropy as the satellites of red hosts, the sample of blue hosts is too small to measure this anisotropy at a statistically-significant level. The anisotropy that we detect for satellites about red primaries is independent of the projected radius. In particular, it is evident at large projected distances from primaries (300 < r_p < 500 kpc). 
Marco Azzaro, Santiago G. Patiri, Francisco Prada, Andrew R. Zentner