Alignments of Radio Galaxies in Deep Radio Imaging of ELAIS N1

Abstract

We present a study of the distribution of radio jet position angles of radio galaxies over an area of 1 square degree in the ELAIS N1 field. ELAIS N1 was observed with the Giant Metrewave Radio Telescope at 612 MHz to an rms noise level of 10 $\mu$Jy and angular resolution of $6"\times 5"$. The image contains 65 resolved radio galaxy jets. The spatial distribution reveals a prominent alignment of jet position angles along a "filament" of about 1$^{\circ}$. We examine the possibility that the apparent alignment arises from an underlying random distribution and find that the probability of chance alignment is less than 0.1%. An angular covariance analysis of the data indicates the presence of spatially coherence in position angles on scales $>0.5^{\circ}$. This angular scales translates to a co-moving scale of $>20h^{-1}$Mpc at a redshift of 1. The implied alignment of the spin axes of massive black holes that give rise the radio jets suggest the presence of large-scale spatial coherence in angular momentum. Our results reinforce prior evidence for large-scale spatial alignments of quasar optical polarisation position angles.