Revisiting the alignment of radio galaxies in the ELAIS-N1 field

Abstract

Aims. Previous studies reported an alignment of the major axes of radio galaxies on various angular scales. Here, we study the alignment of radio galaxies in the ELAIS-N1 Low Frequency ARray (LOFAR) deep field, which covers an area of 25 deg2. Methods. The low noise level of about 20 μJy beam−1 of the LOFAR deep field observations at 150 MHz enabled the identification of 447 extended (> 30″) radio galaxies for which we measured the position angle of the major axis. We find that 95% of these sources have either photometric or spectroscopic redshifts, which we then used for a three-dimensional (3D) analysis. Results. We show the distribution of the position angles of radio galaxies in the ELAIS-N1 field and the results of multiple statistical tests carried out to decipher whether the radio galaxies are randomly oriented. We find that the distribution of position angles is consistent with being uniform. Two peaks around position angles of 50 and 140 deg are spurious and are not caused by an alignment, as shown by a 3D analysis. In conclusion, our results do not support a 2D or 3D alignment of radio galaxies on scales of smaller than ∼4 deg.