Jet reorientation in central galaxies of clusters and groups: insights from VLBA and Chandra data

TL;DR

This study investigates the frequency and causes of jet reorientation in central galaxies of clusters and groups by analyzing VLBA and Chandra data, finding that significant misalignments are common and likely due to intrinsic jet axis changes rather than environmental effects.

Contribution

The paper provides the first systematic analysis of jet-cavity misalignments in galaxy clusters, highlighting the prevalence of jet reorientation and discussing potential engine-based mechanisms.

Findings

30-38% chance of misalignment >45° in observed systems

Projection effects explain only ~35% of large misalignments

Large misalignments up to 90° suggest intrinsic jet reorientation

Abstract

Recent observations of galaxy clusters and groups with misalignments between their central AGN jets and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet - bubble connection in cooling cores, and the processes responsible for jet realignment. To investigate the frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample and selected subsets, we consistently find that there is a 30% - 38% chance to find a misalignment larger than $\Delta\Psi = 45^{\circ}$ when observing a cluster/group with a detected jet and at least one cavity. We determine that projection may account for an apparently large $\Delta\Psi$ only in a fraction of objects ($\sim$35%), and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned systems, we exclude environmental perturbation as the main driver of cavity - jet misalignment. Moreover, we find that large misalignments (up to $\sim90^{\circ}$) are favored over smaller ones ($45^{\circ}\leq\Delta\Psi\leq70^{\circ}$), and that the change in jet direction can occur on timescales between one and a few tens of Myr. We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we discuss several engine-based mechanisms that may cause these dramatic changes.