Anisotropy in the distribution of satellites around primary galaxies in the 2dF Galaxy Redshift Survey: the Holmberg effect

Abstract

We have analysed a sample of satellite and primary galaxies in the 2dF Galaxy Redshift Survey. In our study we find strong statistical evidence of the Holmberg effect (that is, a tendency for satellites to avoid regions along the line defined by the primary plane) within 500 kpc of the projected distance to the primary. This effect is present only when we restrict our analysis to objects with radial velocity relative to the primary |Δν| < 160 km s -1 , which corresponds approximately to the mean of the distribution. We explore the dependence of this anisotropy on spectral type (η), colours and luminosities of both primaries and satellites, finding that objects with a low present-day star formation rate present the most significant effect.