The Composition and Power of the Jet of the Broad-line Radio Galaxy 3C 120

Abstract We calculated the electron–positron pair-production rate at the base of the jet of 3C 120 due to collisions of photons from the hot accretion flow using the measurement of its average soft gamma-ray spectrum by the Compton Gamma Ray Observatory. We found that this rate approximately equals the flow rate of leptons emitting the observed synchrotron radio-to-IR spectrum of the jet core, calculated using the extended jet model following Blandford &amp; Königl. This coincidence shows the jet composition is likely to be pair dominated. We then calculated the jet power in the bulk motion of ions and found it greatly exceeds that achievable by the magnetically arrested disk scenario for the maximum black hole spin unless the jet contains mostly pairs. Next, we found that the magnetic flux through the synchrotron-emitting jet equals the maximum poloidal flux that can thread the black hole. Finally, we compared two estimates of the magnetization parameter at the onset of the synchrotron emission and found they are in agreement only if pairs dominate the jet content.</jats:p

The MeerKAT Massive Distant Clusters Survey: Detection of Diffuse Radio Emission in Galaxy Clusters at z > 1

International audienceDiffuse, low surface-brightness radio emission in merging galaxy clusters provides insights into cosmic structure formation, the growth of magnetic fields, and turbulence. This paper reports a search for diffuse radio emission in a pilot sample of six high-redshift (1.01 < z < 1.31) galaxy clusters from the MeerKAT Massive Distant Cluster Survey (MMDCS). These six clusters are selected as the most massive $(M_{\rm 500c} = 6.7\,- 8.5 \times 10^{14}~\rm{M_{\odot}})$ systems based on their Sunyaev-Zel'dovich mass from the full MMDCS sample of 30 ACT DR5 clusters, and were observed first to explore the high-mass, high-redshift regime. Diffuse radio emission is confidently detected in four clusters and tentatively identified in two, with $k$-corrected radio powers scaled to 1.4 GHz ranging from $(0.46 \pm 0.16)$ to $(4.51 \pm 1.68) \times 10^{24}\, \mathrm{WHz^{-1}}$ and linear sizes between 0.47 and 1.08 Mpc. Combining $Chandra$ X-ray data with MeerKAT radio data, we find that 80$\%$ of clusters with X-ray observations exhibit disturbed morphologies indicative of mergers. These z > 1 galaxy clusters scatter around the established radio power-mass scaling relation observed at lower redshifts, supporting turbulent re-acceleration models in high-redshift mergers. However, their radio spectra are predicted to steepen (\alpha < -1.5) due to enhanced inverse Compton losses in the cosmic microwave background, rendering them under-luminous at 1.4 GHz and placing them below the correlation. Our results demonstrate that merger-driven turbulence can sustain radio halos even at z > 1 while highlighting MeerKAT's unique ability to probe non-thermal processes in the early universe