Millimeter VLBI constraints on the central magnetic field and symmetric jet production in the twin-jet galaxy NGC 1052

¹ Julius-Maximilians-Universität Würzburg, Fakultät für Physik und Astronomie, Institut für Theoretische Physik und Astrophysik, Lehrstuhl für Astronomie, Emil-Fischer-Str. 31, D-97074 Würzburg, Germany
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
³ Department of Space, Earth and Environment, Chalmers University of Technology, SE-41296 Gothenburg, Sweden
⁴ Departament d’Astronomia i Astrofísica, Universitat de València, C/ Dr. Moliner, 50, E-46100 Burjassot, València, Spain
⁵ Observatori Astronòmic, Universitat de València, C/ Catedràtic José Beltrán 2, E-46980 Paterna, València, Spain

^⋆ Corresponding author.

Received: 19 May 2025
Accepted: 28 July 2025

Abstract

Aims. We investigate the symmetry and magnetic field properties of the jets in the radio galaxy NGC 1052, and in particular, the effect of the ionized torus that surrounds the central region on the emitted radiation.

Methods. Our study is based on three new 43 GHz observations with very long-baseline interferometry (VLBI) and on one 86 GHz observation that were conducted between April 2021 and April 2022. We derived the key jet parameters, such as speed, width, and flux density for both jets at the two frequencies and compared them with those obtained from previous VLBI campaigns. Additionally, we present the first (43–86) GHz spectral index image of NGC 1052. This is crucial to assess the role of the torus at high frequencies. Finally, we used the derived observational parameters to constrain the magnetic field strength and configuration in the launched jets.

Results. The jet morphology at 43 GHz varies in the three epochs. This can be associated with the propagation of jet knots that are launched from the nuclear region. The stacked 43 GHz image reveals that the western and receding jet is fainter by approximately three times than its eastern (approaching) counterpart in the submilliarcsecond region. Together with the (43–86) GHz spectral index map, this asymmetry suggests that free–free absorption may affect the 43 GHz emission. In contrast, the jets appear to be highly symmetric at 86 GHz. From the stacked images at 43 GHz and 86 GHz, we extracted the jet width. It is consistent with previous VLBI studies and supports the presence of a parabolic jet profile on very compact scales. Our results suggest overall that the jets are intrinsically launched symmetrically, and that the observed time-dependent asymmetries may result from free–free absorption by the torus and the downstream propagation of jet components. This scenario was supported by previous theoretical studies. Finally, we estimated the magnetic field strength along both jets. Our results agree well with earlier works. We also discuss the possible presence of a magnetically arrested disk in the nuclear region of NGC 1052.