Radio AGN jet alignment: Radio and Optical Position Angle of Radio Galaxies

Abstract

It is well established that AGNs play an important role in the evolution of galaxies. These AGNs can be linked to the accretion processes onto massive black holes and past merger events in their host galaxies, which may lead to different alignments of the jets with respect to the host galaxies. This paper presents a study of the PA differences between radio and optical images of radio AGNs based on the LoTSS DR2, the FIRST, the DESI Legacy Imaging Surveys and the SDSS. We assessed PA measurement biases in the data and classified the radio AGNs based on the radio luminosity and infrared colour from the WISE. This resulted in the largest yet published sample of 3682 radio AGNs with reliable radio and optical PA measurements. The PA difference (dPA) distributions for the radio AGN sample show a prominent minor-axis alignment tendency. Based on some simple assumptions, we simulated the projection effect to estimate the intrinsic jet-galaxy alignment. The observed dPA distribution can be well described by a two-component jet-alignment model in which one component is more aligned with the minor axis of the host galaxy than the other. The fitting results indicate that the jet alignment is dependent on radio luminosity and the shape of the host galaxies, with the jets being more likely to be aligned with the minor axis of the galaxy for lower radio luminosity and for optically more elongated radio AGNs. The minor-axis alignment of the entire sample may suggest a coherent accretion model present in most AGN host galaxies, while a considerable number of luminous radio-AGN with massive host galaxies might have undergone an accretion according to the chaotic model or past merger events.