Probing jet dynamics and collimation in radio galaxies

Context. Radio galaxies with visible two-sided jet structures, such as NGC 1052, are sources of particular interest for studying 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 a jet and a counterjet. Methods. We carried out special relativistic hydrodynamic simulations and performed radiative transfer calculations of an over-pressured perturbed jet. During the radiative transfer calculations, we incorporated both thermal and nonthermal emission, while taking the finite speed of light into account. To further compare our results to observations, we created 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 introduced a semiautomated method of 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 in specific epochs, with one jet evolving near conically and the other one parabolically (the 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 persistent asymmetry in the jet collimation profile of double-sided jet sources and hint at evidence for asymmetrically launched jets.