Jet reorientation revealed by intermittent jet activity in radio galaxy 0954+556

¹ Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China
² School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
³ Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, E-18008 Granada, Spain
⁴ School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China
⁵ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala, Sweden
⁶ School of Physics and Astronomy, Yunnan University, Kunming 650500, China
⁷ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China
⁸ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 150 Science-1 Street, Urumqi 830011, China
⁹ Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS, Beijing 100101, China
¹⁰ Instituto de Estudios Astrofísicos Facultad de Ingeniería y Ciencias Universidad Diego Portales, Av. Ejército 441, Santiago, Chile

^★ Corresponding authors: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 29 December 2024
Accepted: 17 October 2025

Abstract

Context. Intermittent jet activity of active galactic nuclei (AGNs) is a common phenomenon, whereas significant jet reorientation during episodic jet activity in relatively young radio galaxies is rarely reported. The quasar 0954+556 at z = 0.903 is an intriguing source exhibiting an unusual radio jet structure with significantly different jet directions at kiloparsec (kpc) and parsec (pc) scales. At kpc scales, images from the Very Large Array (VLA) exhibit a bright core, a linear jet extending ∼24 kpc to the northwest, and a discrete jet component ∼16 kpc to the northeast. At pc scales, images from the Very Long Baseline Array (VLBA) show a two-component structure with a projected separation of ∼360 pc in the north–south direction.

Aims. The peculiar structure of 0954+556 might result from jet reorientation. Here, our aim was to investigate the possible mechanism via multiscale and multifrequency deep radio images.

Methods. We performed VLA and VLBA observations of 0954+556. Together with some existing data in the NRAO data archive, we made multiple VLA images at 1.4–22 GHz and VLBA images at 1.7–43 GHz for various image analyses of the jet structure.

Results. We identified the location of the radio core at pc scales, detected the faint counter-jets at both pc and kpc scales for the first time, and revealed a diffuse emission region connecting pc- and kpc-scale forward jets. Our spectral index distribution and spectral aging analysis indicate that 0954+556 might undergo at least two episodes of jet activity during the current AGN phase. Moreover, pc-scale polarization maps display a well-resolved spine-sheath polarization structure.

Conclusions. It seems that the jet direction of 0954+556 changed significantly during intermittent jet activity. This may explain the different jet orientations and spectral ages observed from kpc to pc scales. The research provides a strong case that AGN jet direction might change rapidly on timescales of one million years.