[en] Centaurus B is a nearby radio galaxy positioned in the southern hemisphere close to the Galactic plane. Here, in this work, we present a detailed analysis of about 43 months of accumulated Fermi-LAT data of the γ-ray counterpart of the source initially reported in the 2nd Fermi-LAT catalog, and of newly acquired Suzaku X-ray data. We confirm its detection at GeV photon energies and analyze the extension and variability of the γ-ray source in the LAT dataset, in which it appears as a steady γ-ray emitter. The X-ray core of Centaurus B is detected as a bright source of a continuum radiation. We do not detect, however, any diffuse X-ray emission from the known radio lobes, with the provided upper limit only marginally consistent with the previously claimed ASCA flux. Two scenarios that connect the X-ray and γ-ray properties are considered. In the first one, we assume that the diffuse non-thermal X-ray emission component is not significantly below the derived Suzaku upper limit. In this case, modeling the inverse-Compton emission shows that the observed γ-ray flux of the source may in principle be produced within the lobes. This association would imply that efficient in-situ acceleration of the radiating electrons is occurring and that the lobes are dominated by the pressure from the relativistic particles. In the second scenario, with the diffuse X-ray emission well below the Suzaku upper limits, the lobes in the system are instead dominated by the magnetic pressure. In this case, the observed γ-ray flux is not likely to be produced within the lobes, but instead within the nuclear parts of the jet. In conclusion, by means of synchrotron self-Compton modeling, we show that this possibility could be consistent with the broad-band data collected for the unresolved core of Centaurus B, including the newly derived Suzaku spectrum.

[en] We use the integrated polarized radio emission at 1.4 GHz (${\mathrm{\Pi <!--\; ??\; -->}}_{1.4\mathrm{G}\mathrm{H}\mathrm{z}}$) from a large sample of active galactic nuclei (AGN; 796 sources at redshifts $z<<!--\; <\; -->0.7$) to study the large-scale magnetic field properties of radio galaxies in relation to the host galaxy accretion state. We find a fundamental difference in ${\mathrm{\Pi <!--\; ??\; -->}}_{1.4\mathrm{G}\mathrm{H}\mathrm{z}}$ between radiative-mode AGN (i.e., high-excitation radio galaxies (HERGs) and radio-loud QSOs) and jet-mode AGN (i.e., low-excitation radio galaxies (LERGs)). While LERGs can achieve a wide range of ${\mathrm{\Pi <!--\; ??\; -->}}_{1.4\mathrm{G}\mathrm{H}\mathrm{z}}$ (up to ∼30%), the HERGs and radio-loud QSOs are limited to ${\mathrm{\Pi <!--\; ??\; -->}}_{1.4\mathrm{G}\mathrm{H}\mathrm{z}}\lesssim <!--\; ???\; -->15\mathrm{\%<!--\; \%\; -->}$. A difference in ${\mathrm{\Pi <!--\; ??\; -->}}_{1.4\mathrm{G}\mathrm{H}\mathrm{z}}$ is also seen when the sample is divided at 0.5% of the total Eddington-scaled accretion rate, where the weakly accreting sources can attain higher values of ${\mathrm{\Pi <!--\; ??\; -->}}_{1.4\mathrm{G}\mathrm{H}\mathrm{z}}$. We do not find any clear evidence that this is driven by intrinsic magnetic field differences of the different radio morphological classes. Instead, we attribute the differences in ${\mathrm{\Pi <!--\; ??\; -->}}_{1.4\mathrm{G}\mathrm{H}\mathrm{z}}$ to the local environments of the radio sources, in terms of both the ambient gas density and the magnetoionic properties of this gas. Thus, not only are different large-scale gaseous environments potentially responsible for the different accretion states of HERGs and LERGs, we argue that the large-scale magnetized environments may also be important for the formation of powerful AGN jets. Upcoming high angular resolution and broadband radio polarization surveys will provide the high-precision Faraday rotation measure and depolarization data required to robustly test this claim.

[en] Protogalactic environments are typically identified using quasar absorption lines and can manifest as Damped Lyman-alpha Absorbers (DLAs) and Lyman Limit Systems (LLSs). We use radio observations of Faraday effects to test whether these galactic building blocks host a magnetized medium, by combining DLA and LLS detections with 1.4 GHz polarization data from the NRAO VLA Sky Survey (NVSS). We obtain a control, a DLA, and an LLS sample consisting of 114, 19, and 27 lines of sight, respectively. Using a Bayesian framework and weakly informative priors, we are unable to detect either coherent or random magnetic fields in DLAs: the regular coherent fields must be $⩽<!--\; ???\; -->2.8$ μG, and the lack of depolarization suggests the weakly magnetized gas in DLAs is non-turbulent and quiescent. However, we find a mild suggestive indication that LLSs have coherent magnetic fields, with a 71.5% probability that LLSs have higher $|\mathrm{R}\mathrm{M}|$ than a control, although this is sensitive to the redshift distribution. We also find a strong indication that LLSs host random magnetic fields, with a 95.5% probability that LLS lines of sight have lower polarized fractions than a control. The regular coherent fields within the LLSs must be $⩽<!--\; ???\; -->2.4$ μG, and the magnetized gas must be highly turbulent with a typical turbulent length scale on the order of ≈5–20 pc. Our results are consistent with the standard dynamo paradigm, whereby magnetism in protogalaxies increases in coherence over cosmic time, and with a hierarchical galaxy formation scenario, with the DLAs and LLSs exploring different stages of magnetic field evolution in galaxies.