M87, in the Virgo cluster, allows us to study the interaction of a supermassive black hole (SMBH) with its hot gaseous atmosphere. Deep Chandra observations reveal a nearly circular shock front with a Mach number of 1.2 and a radius of 13 kpc which is driven by a central cavity inflated by an SMBH outburst began 12 million years ago. An outburst with an energy of a ~5×57 ergs and a duration of ~2 Myrs provides a good match to all the constraints. For an outburst repetition rate of about 12 Myrs (the outburst age), the outburst energy is sufficient to balance the radiative cooling of the gas. The outburst duration in M87 argues for a “gentle” (long duration) outburst that does not generate strong shocks and where much of the outburst energy is deposited in the cavities that then transfer energy to the surrounding gas as they buoyantly rise.

NGC 1275 has been known as a ppint-like X-ray source with a continuum and a Fe-K line. Unlike radio and GeV/TeV gamma-ray emissions, origin of X-ray emission is not yet understood; is it a jet emission like blazars or an accretion corona emission like Seyfert galaxies. X-ray emission is important to determine the SED of jet emission to constrain jet parameters and also understand the relation between accretion and jet. Here we report a recent X-ray probing of NGC 1275 nuclear region with Hitomi/SXS, Swift/XRT, and Suzaku/XIS. Hitomi/SXS gave the first opportunity to measure a Fe-K line of AGNs with several eV resolution. The line center is consistent with the neutral iron emission, and the width is constrained to be 500-1600 km/s (FWHM). This ruled out the origin of broad line region and inner accretion disk. A low-covering-fraction molecular torus or a rotating molecular disk around pc scales, illuminated by accretion corona emission, is suggested as a possible origin. For the continuum emission, Suzaku/XIS monitor observations revealed that the X-ray flux has gradually increased as the GeV gamma-ray flux. Swift/XRT showed a several-days flux increase, associated with the GeV gamma-ray flare. These results on the continuum emission suggests a contribution of jet emission to the X-ray emission. Based on the combined results of Fe-K line and continuum, we discuss some scenarios for X-ray emitting region.

Radio jets are the large-scale and extragalactic footprints of accretion onto supermassive black holes, and are suggested to be the key ingredient controlling the galaxy stellar mass function. Of particular importance is their jet power - the time-averaged energetic feedback into their environment. Hence, the dynamics, energetics and life-cycles of radio-loud AGN (RLAGN) must be understood in order to build a qualitative and quantitative picture of their impact over cosmic time. Here, we present a study of the spectral age of two powerful, cluster-center radio galaxies, and compare with an analytic model to robustly determine their jet powers. We also present some recent LOFAR observations of the different phases of RLAGN activity, namely the remnant and subsequent restarting phases, which are key to understanding the dynamics of RLAGN over their total lifetime.

The Perseus cluster is the X-ray brightest cluster in the sky and with deep Chandra observations we are able to map its central structure on very short spatial scales. In addition, the high quality of X-ray data allows detailed spatially-resolved spectroscopy. In this paper I review what these deep observations have told us about AGN feedback in clusters, sloshing and instabilities, and the metallicity distribution.

We analyse archival XMM-Newton observations of the massive galaxy group NGC 4839 falling into the Coma cluster core, which reveal a complex morphology for the merger. By comparing high quality X-ray maps of the merging subcluster with SPH simulations, we propose an infall scenario which qualitatively reproduces the observed structure of the NGC 4839 tail.

Several cool-core clusters are known to host a radio mini-halo, a diffuse, steep-spectrum radio source located in their cores, thus probing the presence of non-thermal components as magnetic field and relativistic particles on scales not directly influenced by the central AGN. The nature of the mechanism that produces a population of radio-emitting relativistic particles on the scale of hundreds of kiloparsecs is still unclear. At the same time, it is still debated if the central AGN may play a role in the formation of mini-halos by providing the seed of the relativistic particles. We aim to investigate these open issues by studying the connection between thermal and non-thermal components of the intra-cluster medium. We performed a point-to-point analysis of the radio and the X-ray surface brightness of a compilation of mini-halos. We find that mini-halos have super-linear scalings between radio and X-rays, with radio brightness declining more steeply than the X-ray brightness. This trend is opposite to that generally observed in giant radio halos, thus marking a possible difference in the physics of the two radio sources. Finally, using the scalings between radio and X-rays and assuming a hadronic origin of mini-halos we derive constraints on the magnetic field in the core of the hosting clusters.

Galaxy clusters are excellent targets for high energy astrophysics with gamma rays. Not only they may host active galaxies, but they are often expected to provide signatures of accelerations of electrons and protons to PeV energies. Furthermore, according to ΛCDM scenario, they should be embedded in an extremely massive dark matter halo, the largest halo expected. In this report, we summarize the recently published MAGIC lower limits on the decaying dark matter lifetime using 202 h of selected high quality data taken on the Perseus galaxy cluster, in a 5-year long campaign.

We present the results of a study of the AGN density in a homogeneous and well studied sample of 167 bona-fide X-ray galaxy clusters (0.1<z<0.5). Our aim is to study the AGN activity in 167 XXL X-ray galaxy clusters as a function of the cluster mass and the location of the AGN in the cluster. We report a significant AGN excess in our low-mass cluster sub-sample between 0.5r500 and 2r500. In contrast, the high-mass sub-sample presents no AGN excess. The AGN excess in poor clusters indicates AGN triggering, supporting previous studies that reported enhanced galaxy merging in the cluster outskirts. This effect is probably prevented by high velocity dispersions in high-mass clusters. Comparing also with previous studies of massive or high-redshift clusters, we conclude that the AGN fraction in cluster galaxies anti-correlates strongly with cluster mass.

Radio-mode feedback from relativistic jets is one of the prominent heating mechanisms in clusters of galaxies. We present a long-term evolution of high-resolution MHD simulation of jets interacting with an environment modeled to represent the Perseus cluster. We investigate the thermodynamics of the ICM due to the gas motion triggered by the action of the jets and show that low-entropy gas is lifted efficiently in the wake of the inflating radio lobe. We look into the uplift mechanism and estimate the energy budget and the rate of thermal conduction. The redistribution of entropy suggests that heat conduction can play a more significant role in the thermal evolution of the cluster core in the presence of jets, which act effectively as a heat pump, thus heating the ICM more efficiently than jets would by themselves in an isentropic cluster.

Black holes are usually observed to be of stellar-mass or supermassive. By natural extension, there should be a population of Intermediate-Mass Black Holes (IMBHs: with mass between 100 to 106M⊙) in the Universe; which has started to been observed. An exciting claim has been made recently by Silk (2017): that early feedback by IMBHs in gas-rich dwarf galaxies at z = 5–8, can potentially solve multiple dwarf galaxy problems within the Λ-cold-dark-matter cosmology. We are performing Cosmological Hydrodynamical Simulations of (2Mpc)3 volumes, starting from z = 100, to test the case for IMBHs in Dwarf Galaxies. Black holes of mass 1000M⊙ are seeded inside halos when they reach a mass of 107M⊙. The black holes grow by accretion of gas from their surroundings and by merger with other black holes, and consequently eject feedback energy. We analyze the simulation output in post-processing to study the growth of the first IMBHs, and their impact on star-formation. Our conclusions, based on numerical simulation results, support the phenomenological ideas made by Silk (2017). IMBHs at the centers of dwarf galaxies can be a strong source of feedback to quench star-formation and generate outflows. At the same time, these IMBHs form the missing link between stellar-mass and supermassive BHs.

Thanks to the Fermi λ-ray satellite and the current Imaging Atmospheric Cherenkov Telescopes, radio galaxies have arisen as a new class of high- and very-high energy emitters. The favourable orientation of their jets makes radio galaxies extremely relevant in addressing important issues such as: (i) revealing the jet structure complexity; (ii) localising the emitting region(s) of high- and very-high energy radiation; (iii) understanding the physical processes producing these photons. In this review the main results on the λ-ray emission studies of radio galaxies from the MeV to TeV regimes will be presented, and the impact of future Cherenkov Telescope Array observations will be discussed.

We report the analysis of the gamma-ray variability of NGC 1275–the radio galaxy at the center of the Perseus cluster. NGC 1275 has been observed continuously with the Fermi Large Area Telescope over the last nine years. We applied different time-domain analysis methods including Fourier, wavelets and Bayesian methods, in order to search for quasi-periodic oscillations in the gamma-ray emission. We found no evidence for periodicities of astrophysical origin.

The recent observations in the high energy γ-ray band show that the extragalactic γ-ray sky is dominated by the emission from blazars. However, γ-ray emission from other types of AGNs, e.g., radiogalaxies, also have been detected. These sources were not considered as favored GeV emitters because the nonthermal emission from their jets is less Doppler boosted. Now, the γ-ray emission from more than 25 non-blazar AGNs has been already detected which opened a new window to have an insight into the particle acceleration and emission processes in different components of AGNs. Here, I will present the γ-ray variability of two well-known radiogalaxies, NGC 1275 and 3C 120, which show a rapid flux increase in the γ-ray band.

Observations at high-energies are important to define the first stages of the evolution of extragalactic radio sources and to characterize the interstellar medium of their host galaxies. In some of the X-ray-observed Compact Symmetric Objects (CSOs, among the youngest and most compact radio galaxies), we measured values of the total hydrogen column densities large enough to slow or prevent the radio source growth. The γ-ray window has the potential to constrain the non-thermal contribution of jets and lobes to the total high-energy emission. However, so far, young radio sources remain elusive in γ-rays, with only a handful of detections (or candidates) reported by Fermi. I present our γ-ray study of the CSO PKS 1718–649, and draw comparison with the restarted, γ-ray detected, radio galaxy 3C 84.

As revealed by the Fermi-LAT, blazars represent the dominant population of γ-ray emitters. An essential step for understanding blazar physics and the emission mechanisms is the investigation of a possible connection between the observed low- and high-energy emission. A number of works report on the existence of a significant correlation between radio emission and 0.1-100 GeV γ rays. How does this correlation evolve when very high energy (VHE, E > 0.1 TeV) γ rays are considered? The possible radio-VHE emission connection is still elusive mainly because of the lack of a homogeneous VHE sky coverage. In this work we explore the connection between the parsec-scale radio emission and GeV-TeV γ rays by using two unbiased blazar samples extracted from the 1FHL ( E > 10 GeV) and 2FHL (E > 50 GeV) Fermi catalogs. For comparison, we perform the same analysis by using the 3FGL 0.1-300 GeV γ-ray energy flux. Overall, we find out that there is no significant connection between radio and γ-ray emission above 10 GeV for all the blazar sub-classes with the exception of high synchrotron peaked objects. Conversely, when 0.1-300 GeV γ-ray energies are considered, a strong and significant correlation is found for all of the blazar sub-classes. We interpret these results within the context of the blazar spectral energy distribution properties.

Very high energy (VHE) emission has been detected from the radio galaxy NGC1275, establishing it as a potential cosmic-ray (CR) accelerator and a high energy neutrino source. We here study neutrino and γ-ray emission from the core of NGC1275 simulating the interactions of CRs assumed to be accelerated by magnetic reconnection, with the accreting plasma environment. To do this, we combine (i) numerical general relativistic (GR) magneto-hydrodynamics (MHD), (ii) Monte Carlo GR leptonic radiative transfer and, (iii) Monte Carlo interaction of CRs. A leptonic emission model that reproduces the SED in the [103-1010.5] eV energy range is used as the background target for photo-pion interactions+electromagnetic cascading. CRs injected with the power-law index κ=1.3 produce an emission profile that matches the VHE tail of NGC1275. The associated neutrino flux, below the IceCube limits, peaks at ∼PeV energies. However, coming from a single source, this neutrino flux may be an over-estimation.

An abundance of information about the magnetic (B) fields of relativistic AGN jets has been obtained through radio polarization observations made on a wide range of scales, from the parsec scales probed by Very Long Baseline Interferometry to the kiloparsec scales probed by instruments such as the the Jansky Very Large Array and e-MERLIN. The observed radio emission is synchrotron radiation, for which the linear polarization angles in optically thin regions is orthogonal to the local synchrotron B fields. The characteristic B field structures observed for these jets on parsec scales are described. A key question is whether B field structures observed in particular AGN jets come about primarily due to “global” effects such as the intrinsic B field of the jet itself, which is expected to be helical, or local phenomena such as shocks, shear and bending of the jets. Observational criteria that can be used to try to distinguish between various possible origins for observed B field structures are described. There is now considerable evidence that the relativistic jets of AGNs do indeed carry helical B fields, with the observed polarization also sometimes appreciably influenced by local effects. Patterns seen in the helical B field components, indicated for example by Faraday rotation observations, provide unique information about the processes involved in the generation of these helical B fields. The collected observations on parsec and kiloparsec scales provide weighty evidence that an important role is played by the action of a cosmic “battery” that acts to generate an inward current along the jet axis and an outward current in a more extended region surrounding the jet.

The magneto hydrodynamic models of relativistic jets from active galactic nuclei predict the jet power transported by the Poynting flux at the jet base, setting the correlation between the jet power and the total magnetic flux. For highly collimated jets taking the transversal structure into account allows to rewrite this correlation through the observed jet properties such as spectral flux and core shift. Applying this method we find that, for the sample of 48 sources, their jet power distribution is well peaked at the theoretically predicted level.

It is still a mystery why only a small fraction of quasars contain relativistic jets. A strong magnetic field is a necessary ingredient for jet formation. Gas falls from the Bondi radius RB nearly freely to the circularization radius Rc, and a thin accretion disk is formed within Rc We suggest that the external weak magnetic field threading interstellar medium is substantially enhanced in this region, and the magnetic field at Rc can be sufficiently strong to drive outflows from the disk if the angular velocity of the gas is low at RB. In this case, the magnetic field is efficiently dragged in the disk, because most angular momentum of the disk is removed by the outflows that lead to a significantly high radial velocity. The strong magnetic field formed in this way may accelerate jets in the region near the black hole, either by the Blandford-Payne or/and Blandford-Znajek mechanisms. If the angular velocity of the circumnuclear gas is low, the field advection in the thin disk is inefficient, and it will appear as a radio-quiet (RQ) quasar.

In galactic nuclei (AGN), the kinetic energy flux of the jet may exceed the bolometric luminosity of the disk a few orders of magnitude. At the “cold” accretion the radiation from the disk is suppressed because the wind from the disk carries out almost all the angular momentum and the gravitational energy of the accreted material. We calculate an unavoidable radiation from such a disk and the ratio of the kinetic-to-bolometric luminosity from a super massive black hole in framework of the paradigm of the optically thick α-disk of Shakura & Sunyaev. The results confirm that the gravitational energy of the accreted material can be the only source of energy in AGNs.