scholarly journals Feeding of active galactic nuclei by dynamical perturbations

2019 ◽  
Vol 492 (1) ◽  
pp. 603-614
Author(s):  
Matas Tartėnas ◽  
Kastytis Zubovas
Keyword(s):  
Active Galactic Nuclei ◽  
Feeding Rate ◽  
Galactic Nuclei ◽  
Accretion Disc ◽  
High Impact ◽  
Galactic Centre ◽  
Supermassive Black Hole ◽  
Disc Model ◽  
Limiting Values ◽  
Significant Mass

ABSTRACT There possibly was an active galactic nuclei (AGN) episode in the Galactic Centre (GC) about 6 Myr ago, powerful enough to produce the Fermi bubbles. We present numerical simulations of a possible scenario giving rise to an activity episode: a collision between a central gas ring surrounding the supermassive black hole (SMBH) and an infalling molecular cloud. We investigate different initial collision angles between the cloud and the ring. We follow the hydrodynamical evolution of the system following the collision using gadget-3 hybrid N-body/SPH code and calculate the feeding rate of the SMBH accretion disc. This rate is then used as an input for a 1D thin α-disc model in order to calculate the AGN luminosity. By varying the disc feeding radii, we determine the limiting values for possible AGN accretion disc luminosity. Small angle collisions do not result in significant mass transport to the centre of the system, while models with highest collision angles transport close to $40{{\ \rm per\ cent}}$ of the initial matter to the accretion disc. Even with ring and cloud masses equal to $10^4 \, {\rm M_{\odot }}$, which is the lower limit of present-day mass of the circumnuclear ring in the GC, the energy released over an interval of 1.5 Myr can produce $\sim 10{{\ \rm per\ cent}}$ of that required to inflate the Fermi bubbles. If the gas ring in the GC 6 Myr ago had a mass of at least $10^5 \, {\rm M_{\odot }}$, our proposed scenario can explain the formation of the Fermi bubbles. We estimate that such high-impact collisions might occur once every ∼108 yr in our Galaxy.

scholarly journals Non-isotropic feedback from accreting spinning black holes

2020 ◽  
Vol 500 (4) ◽  
pp. 4788-4800
Author(s):  
Luca Sala ◽  
Elia Cenci ◽  
Pedro R Capelo ◽  
Alessandro Lupi ◽  
Massimo Dotti
Keyword(s):  
Black Holes ◽  
Active Galactic Nuclei ◽  
Surrounding Medium ◽  
Galactic Nuclei ◽  
Accretion Disc ◽  
Test Bed ◽  
Host Galaxies ◽  
Massive Black Holes ◽  
Disc Model ◽  
Comparable Mass

ABSTRACT Active galactic nuclei (AGNs) are massive black holes (BHs) caught in the act of accreting gas at the centre of their host galaxies. Part of the accreting mass is converted to energy and released into the surrounding medium, in a process loosely referred to as AGN feedback. Most numerical simulations include AGN feedback as a sub-grid model, wherein energy or momentum (or both) is coupled to the nearby gas. In this work, we implement a new momentum-driven model in the hydrodynamics code gizmo, in which accretion from large scales is mediated by a sub-grid accretion disc model, and gas particles are stochastically kicked over a bi-conical region, to mimic observed kinetic winds. The feedback cone’s axis can be set parallel either to the angular momentum of the gas surrounding the BH or to the BH spin direction, which is self-consistently evolved within the accretion-disc model. Using a circumnuclear disc (CND) as a test bed, we find that (i) the conical shape of the outflow is always visible and is weakly dependent on the launching orientation and aperture, resulting in comparable mass inflows and outflows; (ii) the cone’s orientation is also similar amongst our tests, and it is not always the same as the initial value, due to the interaction with the CND playing a crucial role in shaping the outflow; and (iii) the velocity of the outflow, instead, differs and strongly depends on the interplay with the CND.

scholarly journals The ecology of the galactic centre: Nuclear stellar clusters and supermassive black holes

2019 ◽  
Vol 14 (S351) ◽  
pp. 80-83 ◽  
Author(s):  
Melvyn B. Davies ◽  
Abbas Askar ◽  
Ross P. Church
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Large Fraction ◽  
Galactic Nuclei ◽  
Supermassive Black Holes ◽  
Galactic Centre ◽  
Stellar Clusters ◽  
Stellar Cluster ◽  
Supermassive Black Hole ◽  
Multiple Clusters

AbstractSupermassive black holes are found in most galactic nuclei. A large fraction of these nuclei also contain a nuclear stellar cluster surrounding the black hole. Here we consider the idea that the nuclear stellar cluster formed first and that the supermassive black hole grew later. In particular we consider the merger of three stellar clusters to form a nuclear stellar cluster, where some of these clusters contain a single intermediate-mass black hole (IMBH). In the cases where multiple clusters contain IMBHs, we discuss whether the black holes are likely to merge and whether such mergers are likely to result in the ejection of the merged black hole from the nuclear stellar cluster. In some cases, no supermassive black hole will form as any merger product is not retained. This is a natural pathway to explain those galactic nuclei that contain a nuclear stellar cluster but apparently lack a supermassive black hole; M33 being a nearby example. Alternatively, if an IMBH merger product is retained within the nuclear stellar cluster, it may subsequently grow, e.g. via the tidal disruption of stars, to form a supermassive black hole.

scholarly journals Disentangling AGN and starburst activities in NGC 6240 from an X-ray perspective

2014 ◽  
Vol 10 (S312) ◽  
pp. 36-38
Author(s):  
Junfeng Wang
Keyword(s):  
Active Galactic Nuclei ◽  
Large Scale ◽  
Imaging Spectroscopy ◽  
Galactic Nuclei ◽  
Resolving Power ◽  
High Excitation ◽  
X Ray ◽  
Supermassive Black Hole ◽  
X Ray Imaging ◽  
High Temperature Gas

AbstractThe circum-nuclear region in an active galaxy is often complex with presence of high excitation gas, collimated radio outflow, and star formation activities, besides the actively accreting supermassive black hole. The unique spatial resolving power of Chandra X-ray imaging spectroscopy enables more investigations to disentangle the active galactic nuclei and starburst activities. For galaxies in the throes of a violent merging event such as NGC6240, we were able to resolve the high temperature gas surrounding its binary active black holes and discovered a large scale soft X-ray halo.

2.9. Microlens mapping of disks in active galactic nuclei

1998 ◽  
Vol 184 ◽  
pp. 75-76 ◽  
Author(s):  
A. Yonehara ◽  
S. Mineshige ◽  
J. Fukue ◽  
M. Umemura ◽  
E.L. Turner
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Accretion Disk ◽  
Central Region ◽  
Galactic Nuclei ◽  
Direct Information ◽  
Supermassive Black Hole ◽  
Disk Size

Generally, it is believed that there is a supermassive black hole and a surrounding accretion disk in a central region of active galactic nuclei (AGN). However, it is quite difficult to obtain direct information about the center of AGN, because the accretion disk size is far too small to resolve.

Determination of supermassive black hole spins in active galactic nuclei

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040054
Author(s):  
M. Yu. Piotrovich ◽  
V. L. Afanasiev ◽  
S. D. Buliga ◽  
T. M. Natsvlishvili
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Active Galactic Nuclei ◽  
Accretion Disk ◽  
Galactic Nuclei ◽  
Supermassive Black Holes ◽  
Disk Model ◽  
Supermassive Black Hole

Based on spectropolarimetry for a number of active galactic nuclei in Seyfert 1 type galaxies observed with the 6-m BTA telescope, we have estimated the spins of the supermassive black holes at the centers of these galaxies. We have determined the spins based on the standard Shakura-Sunyaev accretion disk model. More than 70% of the investigated active galactic nuclei are shown to have Kerr supermassive black holes with a dimensionless spin greater than 0.9.

scholarly journals Detection of a double-peaked H α component from the accretion disc of NGC 4958

2019 ◽  
Vol 486 (1) ◽  
pp. 1138-1145
Author(s):  
T V Ricci ◽  
J E Steiner
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Outer Radius ◽  
Accretion Disc ◽  
Line Of Sight ◽  
Broad Component ◽  
Line Region ◽  
Inner Radius ◽  
The Galaxy ◽  
Narrow Line Region

Abstract Active Galactic Nuclei are objects associated with the presence of an accretion disc around supermassive black holes found in the very central region of galaxies with a well-defined bulge. In the optical range of the spectrum, a possible signature of the accretion disc is the presence of a broad double-peaked component that is mostly seen in H α. In this paper, we report the detection of a double-peaked feature in the H α line in the nucleus of the galaxy NGC 4958. The narrow-line region of this object has an emission that is typical of a low-ionization nuclear emission-line region galaxy, which is the usual classification for double-peaked emitters. A central broad component, related to the broad-line region of this object, is seen in H α and also in H β. We concluded that the double-peaked emission is emitted by a circular relativistic Keplerian disc with an inner radius ξi  = 570 ± 83, an outer radius ξo  = 860 ± 170 (both in units of GMSMBH/c2), an inclination to the line of sight i = 27.2 ± 0.7° and a local broadening parameter σ  = 1310 ± 70 km s−1.

scholarly journals Non-equilibrium chemistry and destruction of CO by X-ray flares

2019 ◽  
Vol 486 (1) ◽  
pp. 1094-1122 ◽  
Author(s):  
Jonathan Mackey ◽  
Stefanie Walch ◽  
Daniel Seifried ◽  
Simon C O Glover ◽  
Richard Wünsch ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Thermal Evolution ◽  
Galactic Nuclei ◽  
Galactic Centre ◽  
X Rays ◽  
X Ray ◽  
Uv Emission ◽  
Sgr A ◽  
X Ray Binaries ◽  
Fractal Cloud

ABSTRACT Sources of X-rays such as active galactic nuclei and X-ray binaries are often variable by orders of magnitude in luminosity over time-scales of years. During and after these flares the surrounding gas is out of chemical and thermal equilibrium. We introduce a new implementation of X-ray radiative transfer coupled to a time-dependent chemical network for use in 3D magnetohydrodynamical simulations. A static fractal molecular cloud is irradiated with X-rays of different intensity, and the chemical and thermal evolution of the cloud are studied. For a simulated $10^5\, \mathrm{M}_\odot$ fractal cloud, an X-ray flux <0.01 erg cm−2 s−1 allows the cloud to remain molecular, whereas most of the CO and H2 are destroyed for a flux of ≥1 erg cm−2 s−1. The effects of an X-ray flare, which suddenly increases the X-ray flux by 105×, are then studied. A cloud exposed to a bright flare has 99 per cent of its CO destroyed in 10–20 yr, whereas it takes >103 yr for 99 per cent of the H2 to be destroyed. CO is primarily destroyed by locally generated far-UV emission from collisions between non-thermal electrons and H2; He+ only becomes an important destruction agent when the CO abundance is already very small. After the flare is over, CO re-forms and approaches its equilibrium abundance after 103–105 yr. This implies that molecular clouds close to Sgr A⋆ in the Galactic Centre may still be out of chemical equilibrium, and we predict the existence of clouds near flaring X-ray sources in which CO has been mostly destroyed but H is fully molecular.

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