Shape Alignments of Satellite Galaxies

Abstract

We test a sample of satellites of isolated primary galaxies, extracted from the 2dF Galaxy Redshift Survey (2dFGRS), for any tendency to be aligned along (or against) the primary-to-satellite radius vector. If tidal effects induce such an alignment, it would contaminate recent measurements of galaxy halo masses which use the coherent alignment induced on background galaxies by gravitational lensing. The mean tangential ellipticity of 1819 satellites within 500 kpc projected radius is <e_+> = +0.004+-0.008, so no tidal alignment is detected. This implies at 95% confidence that satellite alignment is less than a 20% contamination of the alignment signal attributed to galaxy-galaxy lensing by Smith et al. (2001) and McKay et al. (2001).