Large-scale, broad outflows are common in active galaxies. In systems where star formation coexists with an AGN, it is unclear yet the role that both play on driving the outflows. In this work we present three-dimensional radiative-cooling MHD simulations of the formation of these outflows, considering the feedback from both the AGN and supernovae-driven winds. We find that a large-opening-angle AGN wind develops fountain structures that make the expanding gas to fallback. Furthermore, it exhausts the gas near the nuclear region, extinguishing star formation and accretion within a few 100.000 yr, which establishes the duty cycle of these outflows. The AGN wind accounts for the highest speed features in the outflow with velocities around 10.000 km s−1 (as observed in UFOs), but these are not as cold and dense as required by observations of molecular outflows. The SNe-driven wind is the main responsible for the observed mass-loading of the outflows.

Very Long Baseline Interferometry (VLBI) at sub-millimeter waves has the potential to image the shadow of the black hole in the Galactic Center, Sagittarius A* (Sgr A*), and thereby test basic predictions of the theory of general relativity. We investigate the imaging prospects of a new Space VLBI mission concept. The setup consists of two satellites in polar or equatorial circular Medium-Earth Orbits with slightly different radii, resulting in a dense spiral-shaped uv-coverage with long baselines, allowing for extremely high-resolution and high-fidelity imaging of radio sources. We simulate observations of a general relativistic magnetohydrodynamics model of Sgr A* for this configuration with noise calculated from model system parameters. After gridding the uv-plane and averaging visibilities accumulated over multiple months of integration, images of Sgr A* with a resolution of up to 4 μ as could be reconstructed, allowing for stronger tests of general relativity and accretion models than with ground-based VLBI.

Observations of low luminosity active galactic nuclei (LLAGNs) and the hard state of black hole X-ray binaries (BHBs) show that the wind exists. Black hole in LLAGNs and hard state of BHBs accretes gas in hot accretion mode. In this paper, we first use magnetohydrodynamic (MHD) simulations of hot accretion flow around a black hole to study the origin of the wind. We find that the wind is driven by the combination of gradients of gas and magnetic pressure and centrifugal forces. Second, we use simulations with focus on the region around Bondi radius to study whether the wind can be generated outside Bondi radius. In the simulation studying hot accretion flow around Bondi radius, in addition to the black hole gravity, we also take into account the gravity of nuclei stars. We find that the wind can not be generated outside Bondi radius. The absence of the wind is due to the change of gravity potential.

We investigate the sample of 16 the youngest radio galaxies with measured kinematic ages and available X-ray data from high-resolution Chandra or XMM-Newton observations. We characterize the accretion properties and derive the jet kinetic luminosities for our sources. We found high accretion rates (>1% Eddington) and very high jet production efficiency for all the sources from our sample.This, along with the fact that the analyzed objects seem over-luminous in radio on the fundamental plane for the black hole activity, implies also that the radiative efficiency of the compact lobes is much higher than in the case of the evolved radio galaxies.

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.

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.

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.

Tidal Disruption Events (TDEs) are a common feature between Active and Quiescent Galactic Nuclei; the study of these events is a very useful tool to probe phenomena that relate to the formation of an accretion disc or a jet. Also, the accretion rate at the beginning of the tidal flare is expected to be significantly super-Eddington and might result in high energy emission (in soft X-rays but sometimes up to the gamma regime, as in the the case of Swift J1644, see Komossa 2015). These events may even play an important role in the newborn field of the Multimessenger Astronomy. This work is set within this context. Indeed, it is a study of generation of Gravitational Waves (GWs) from the hot accreting torus resulting after a TDE. Since the torus has only formed recently, magnetic fields are not expected to be strong enough, so that the torus is likely to be unstable to the Papaloizou-Pringle Instability (PPI), producing a strongly varying mass quadrupole. Here, the study of the evolution of such tori is developed, using both analytical calculation and a Smoothed Particle Hydrodynamics simulation (SPH). In particular the goal of this work is to determine the GW waveform and to compute the characteristic strain of these GWs in order to see if they are detectable by the Laser Interferometer Space Antenna (LISA).

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 fully analytical solution for isothermal Bondi accretion on a black hole (MBH) at the center of JJ two-component Jaffe (1983) galaxy models is presented. In JJ models the stellar and total mass density distributions are described by the Jaffe profile, with different scale-lengths and masses, and to which a central MBH is added; all the relevant stellar dynamical properties can also be derived analytically. In these new accretion solutions the hydrodynamical and stellar dynamical properties are linked by imposing that the gas temperature is proportional to the virial temperature of the stellar component. The formulae that are provided allow to evaluate all flow properties, and are then useful for estimates of the accretion radius and the mass flow rate when modeling accretion on MBHs at the center of galaxies.

Radio-loud Active Galactic Nuclei (AGN) produce relativistic jets that can be modelled with relativistic hydrodynamic (RHD) simulations. In this study we present two such simulations of jets, used to investigate the parameters required to reproduce structures consistent with both FR I and FRII jets. In the first simulation a Lorentz factor of 10 and supersonic flow of Mach 30 were chosen, while for the second simulation a Lorentz factor of 1.0014 with a supersonic flow of Mach 4 was used. Over similar distances scales the first case shows a well collimated beam with a strong shock at the interface between the jet and ambient medium while the second case shows a less stable beam and a larger cocoon. To determine whether the simulated physical structures are consistent with the observed FR I/II jets, the synchrotron emission has been calculated to produce radio maps at a single frequency of 1.5 GHz.

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.

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.

By constructing images of the Faraday rotation measure (RM) of large scale astrophysical jets, the line-of-sight magnetic field component and electron density in the region of Farady rotation can be investigated. A significant gradient in the RM transverse to the jet direction may indicate a corresponding gradient in the line-of-sight magnetic field, implying a toroidal or helical magnetic field, which would, in turn, imply the presence of an associated electrical current in the jet. The detection of such large scale gradients can reliably demonstrate that helical or toroidal fields can persist to large distances from the central AGN. We present a kiloparsec-scale Faraday rotation map of NGC 6251 that shows statistically significant transverse RM gradients across its kiloparsec scale jet structure that imply an outward current.

The occurence rate of tidal disruption events (TDEs) by survey missions depend on the black hole mass function of the galaxies, properties of the stellar cusp and mass of the central black hole. Using a power law density profile with Kroupa mass function, we solve the steady state Fokker-Planck to calculate the theoretical capture rate of stars by the black hole. Using a steady accretion model, the Schechter black hole mass function (BHMF) and the cosmological parameters, we calculate the detection rate of TDEs for various surveys which is then fit with the observed TDE rates to extract the Schechter parameters. The rate tension between observation (∼10−5yr−1) and theory (∼10−4yr−1 for individual galaxies is explained by the statistical average over the BHMF.

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.

I report observations of 3C84 (NGC 1275), the central galaxy of the Perseus cluster, made with an interferometric array including the orbiting radio telescope of the RadioAstron mission. The data transversely resolve the edge-brightened jet in 3C84 only 0.03 mas from the core, which is ten times closer to the central engine than was possible in previous ground-based observations. To better understand physical properties of this peculiar source, I will discuss its present properties in comparison to the past and more recent evolution in the radio band of 3C 84.

Following the discovery of the expansion of a young radio lobe associated with the bright radio source 3C 84 in the Seyfert galaxy NGC 1275 using VSOP monitoring observation with duration of 3 years, we further investigated its evolution by utilizing VLBA monitoring data taken by MOJAVE project. As the results, we confirmed the expanding motion of both the southern and northern lobes, and detected side-way expanding motions for the first time. In meantime, the total flux density of the lobes are decreasing, while total flux density associated with the nuclei is significantly increasing. This cooling of the radio lobe can be well-explained with the energy loss through the adiabatic cooling.

An understanding of the mechanisms that regulate the Active Galactic Nuclei passes through the study of their early life stages, observable in Compact Symmetric Objects. To this purpose, a study was carried out on two compact radio sources, based on data from the VLBA archive at different times and frequencies. The results are compatible with an intermediate scenario between the two main theories about these objects: frustration and youth.

We present a new method for supermassive black hole (SMBH) mass measurements in Type 1 active galactic nuclei (AGN) using polarization angle across broad lines. This method gives measured masses which are in a good agreement with reverberation estimates. Additionally, we explore the possibilities and limits of this method using the STOKES radiative transfer code taking a dominant Keplerian motion in the broad line region (BLR). We found that this method can be used for the direct SMBH mass estimation in the cases when in addition to the Kepler motion, radial inflows or vertical outflows are present in the BLR. Some advantages of the method are discussed.