Lopsided Satellite Distributions around Isolated Host Galaxies

We investigate the spatial distribution of the satellites of bright, isolated host galaxies. In agreement with previous studies, we find that, on average, the satellites of red hosts are found preferentially close to their hosts' major axes, while the satellites of blue hosts are distributed isotropically. We compute the pairwise clustering of the satellites and find a strong tendency for pairs of satellites to be located on the same side of their host, resulting in lopsided spatial distributions. The signal is most pronounced for the satellites of blue hosts, where the number of pairs on the same side of their host exceeds the number of pairs on opposite sides of their host by a factor of 1.8 ± 0.1. For the satellites of red hosts, the number of pairs on the same side of their host exceeds the number of pairs on opposite sides of their host by a factor of 1.08 ± 0.03. Satellites that are far from their hosts (rp ≳ 300 kpc) show a strong preference for being located on the same side of their hosts; satellites that are near to their hosts (rp ≲ 100 kpc) show a weak preference for being located on opposite sides of their hosts. While lopsided distributions have been found previously for the satellites of bright pairs of galaxies, ours is the first study to find lopsided distributions for the satellites of isolated bright galaxies.