A NEW THEORY FOR THE ALIGNMENT EFFECT

In this paper I propose a new explanation of the strong alignments seen between the infrared, optical, and radio structures of high-redshift radio galaxies. This theory is based on the assumption that the anisotropy of the optical/infrared emission around a typical high-redshift radio galaxy implies the surrounding density distribution is also anisotropic. In most models of double radio sources the luminosity of the source increases with the density of the surrounding gas. So if a radio source is expanding out into ps whose density distribution is not spherically symmetric, its average luminosity will be greatest if it is expanding along the major axis of the gas distribution. As most of the sources in a flux-limited sample are close to the lower flux limit of the sample, this leads to a strong selection effect: flux-limited samples will preferentially contain plaxies in which the axes of the radio emission and of the gas distribution are aligned. I show quantitatively for the 3C sample that an effect of this kind is sufficient to explain the observed alignment effect. The new theory makes the prediction that the alignment effect should be as strong in faint samples as in bright samples, in contrast to the popular starburst model which predicts the alignment effect should be much weaker in faint samples. Preliminary evidence favors the new model.