The twisted jets and magnetic fields of the extended radio galaxy 4C 70.19^⋆⋆

¹ Obserwatorium Astronomiczne Uniwersytetu Jagiellońskiego, ul. Orla 171, 30-244 Kraków, Poland
² Centre for Astrophysics Research, Department of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
³ CSIRO Astronomy and Space Science, PO Box 1130 Bentley, WA 6102, Australia
⁴ ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands

^⋆ Corresponding author; markmet@oa.uj.edu.pl

Received: 19 July 2024
Accepted: 16 September 2024

Abstract

Context. The appearance of the jets and lobes of some radio galaxies makes it difficult to assign them to a known class of objects. This is often due to the activity of the central engine and/or interactions with the environment, as well as projection effects.

Aims. We analyse the radio data for an apparently asymmetric radio source 4C 70.19, which is associated with the giant elliptical galaxy NGC 6048. The source shows distorted radio jets and lobes, one of which bends by 180°. The aim of our study is to explain the nature of the observed distortions.

Methods. We used LOFAR, Effelsberg, and VLA radio data in a wide range of frequencies. At high frequencies, we also used radio polarimetry to study the properties of the magnetic fields. Additionally, we made use of optical, infra-red, and X-ray data.

Results. Polarisation data suggest shearing of the magnetic fields at points where the jets bend. The low-frequency LOFAR map at 145 MHz, as well as the sensitive single-dish Effelsberg map at 8.35 GHz, reveal previously undetected diffuse emission around the source. The rotation measure (RM) derived from the polarimetric data allowed us to estimate the density of the medium surrounding the source, which agrees with typical densities of the intergalactic medium or the outer parts of insterstellar halos.

Conclusions. We propose that the southern jet is bent in the same manner as the northern one, but that it is inclined to the sky plane. Both these bends are likely caused by the orbital motion within the galaxy group, as well as interactions with the intergalactic medium. Our analyses suggest that, despite its complex morphology, 4C 70.19 seems to be intrinsically symmetric with a physical extent of up to 600 kpc, and that the diffuse emission detected in our high-sensitivity maps is related to radio plumes that are expanding behind the source.