Probing jet dynamics and collimation in radio galaxies. Application to NGC 1052

TL;DR

This study uses relativistic hydrodynamic simulations and radiative transfer modeling to investigate how shocks can cause apparent asymmetries in the jets of radio galaxies like NGC 1052, highlighting the importance of intrinsic jet asymmetry.

Contribution

The paper introduces a combined simulation and observational approach to distinguish between apparent and intrinsic jet asymmetries in radio galaxies.

Findings

Propagating shocks can create temporary asymmetries in jet collimation profiles.

Observed asymmetries may be due to relativistic effects and time delays, not intrinsic differences.

Persistent asymmetries suggest the presence of genuinely asymmetrically launched jets.

Abstract

Context. Radio galaxies with visible two-sided jet structures, such as NGC 1052, are sources of particular interest to study the collimation and shock structure of active galactic nuclei jets. High-resolution very-long-baseline interferometry observations of such sources can resolve and study the jet collimation profile and probe different physical mechanisms. Aims. In this paper, we study the physics of double-sided radio sources at parsec scales, and in particular investigate whether propagating shocks can give rise to the observed asymmetry between jet and counterjet. Methods. We carry out special relativistic hydrodynamic simulations and perform radiative transfer calculations of an over-pressured perturbed jet. During the radiative transfer calculations we incorporate both thermal and nonthermal emission while taking the finite speed of light into account. To further compare our results to observations, we create more realistic synthetic data including the properties of the observing array as well as the image reconstruction via multifrequency regularized maximum likelihood methods. We finally introduce a semi-automatized method for tracking jet components and extracting jet kinematics. Results. We show that propagating shocks in an inherently symmetric double-sided jet can lead to partially asymmetric jet collimation profiles due to time delay effects and relativistic beaming. These asymmetries may appear on specific epochs, with one jet evolving near conically and the other one parabolically (width profile evolving with a slope of 1 and 0.5, respectively). However, these spurious asymmetries are not significant when observing the source evolve for an extended amount of time. Conclusions. Purely observational effects are not enough to explain a persisting asymmetry in the jet collimation profile of double-sided jet sources and hint at evidence for asymmetrically launched jets.