Thin synchrotron-emitting filaments are increasingly seen in the intracluster medium (ICM). We present the first example of a direct interaction between a magnetic filament, a radio jet, and a dense ICM clump in the poor cluster A194. This enables the first exploration of the dynamics and possible histories of magnetic fields and cosmic rays in such filaments. Our observations are from the MeerKAT Galaxy Cluster Legacy Survey and the LOFAR Two-Meter Sky Survey. Prominent 220 kpc long filaments extend east of radio galaxy 3C40B, with very faint extensions to 300 kpc, and show signs of interaction with its northern jet. They curve around a bend in the jet and intersect the jet in Faraday depth space. The X-ray surface brightness drops across the filaments; this suggests that the relativistic particles and fields contribute significantly to the pressure balance and evacuate the thermal plasma in a ∼35 kpc cylinder. We explore whether the relativistic electrons could have streamed along the filaments from 3C40B, and present a plausible alternative whereby magnetized filaments are (a) generated by shear motions in the large-scale, post-merger ICM flow, (b) stretched by interactions with the jet and flows in the ICM, amplifying the embedded magnetic fields, and (c) perfused by re-energized relativistic electrons through betatron-type acceleration or diffusion of turbulently accelerated ICM cosmic-ray electrons. We use the Faraday depth measurements to reconstruct some of the 3D structures of the filameGnts and of 3C40A and B.

We report from a study utilizing 3D MHD simulations, including cosmic-ray electrons, of the interactions between radio galaxies (RGs) and dynamically active intracluster media (ICMs). Here we consider interactions involving plane ICM shocks having Mach numbers 2–4 and their normals aligned with steady, active bipolar RG jets penetrating uniform, stationary ICMs. The shock impact disrupts the preformed RG jet cocoons into ring vortex structures. Sufficiently strong post-shock winds can stop and even reverse the upwind jet and strip jets to virtually naked states, leaving them without a surrounding cocoon. Strong shock-induced vorticity can also disrupt the downwind jet, so that the ring vortex remnant of the cocoons appears ahead of that jet’s visible terminus. Magnetic field amplification in the ring vortex can significantly enhance its synchrotron emissions well after the vortex becomes isolated from the RG and its fresh cosmic-ray electron supply. We examine these dynamics and their observable consequences in detail.

In this paper, we lay out a simple set of relationships connecting the dynamics of fast plasma jets to the dynamical state of their ambient media. The objective is to provide a tool kit that can be used to connect the morphologies of radio active galactic nuclei (AGNs) in galaxy clusters to the dynamical state of the local intracluster medium (ICM). The formalism is intended to apply to either relativistic or non-relativistic jets. Special attention is paid to interactions involving ICM shocks, although the results can be applied more broadly. Our formalism emphasizes the importance of the relative Mach number of the impacting ICM flow and the internal Mach number of the AGN jet in determining how the AGN outflows evolve.

Although many of the observed properties of giant radio relics detected in the outskirts of galaxy clusters can be explained by relativistic electrons accelerated at merger-driven shocks, significant puzzles remain. In the case of the so-called Toothbrush relic, the shock Mach number estimated from X-ray observations ( ) is substantially weaker than that inferred from the radio spectral index ( ). Toward understanding such a discrepancy, we here consider the following diffusive shock acceleration (DSA) models: (1) weak-shock models with and a preexisting population of cosmic-ray electrons (CRe) with a flat energy spectrum, and (2) strong-shock models with and either shock-generated suprathermal electrons or preexisting fossil CRe. We calculate the synchrotron emission from the accelerated CRe, following the time evolution of the electron DSA, and the subsequent radiative cooling and postshock turbulent acceleration (TA). We find that both models could reproduce reasonably well the observed integrated radio spectrum of the Toothbrush relic, but the observed broad transverse profile requires the stochastic acceleration by downstream turbulence, which we label “turbulent acceleration” or TA to distinguish it from DSA. Moreover, to account for the almost uniform radio spectral index profile along the length of the relic, the weak-shock models require a preshock region over 400 kpc with a uniform population of preexisting CRe with a high cutoff energy ( ). Due to the short cooling time, it is challenging to explain the origin of such energetic electrons. Therefore, we suggest the strong-shock models with low-energy seed CRe ( ) are preferred for the radio observations of this relic.