scholarly journals Effects of opacity temperature dependence on radiatively accelerated clouds

2020 ◽  
Vol 493 (1) ◽  
pp. 437-445
Author(s):  
Sergei Dyda ◽  
Daniel Proga ◽  
Christopher S Reynolds
Keyword(s):  
Active Galactic Nuclei ◽  
Radiation Flux ◽  
Dynamical Evolution ◽  
Galactic Nuclei ◽  
Incident Radiation ◽  
Time Dependent ◽  
Radiation Hydrodynamics ◽  
Temperature Relation ◽  
Bright Side ◽  
Rocket Effect

ABSTRACT We study how different opacity–temperature scalings affect the dynamical evolution of irradiated gas clouds using time-dependent radiation-hydrodynamics simulations. When clouds are optically thick, the bright side heats up and expands, accelerating the cloud via the rocket effect. Clouds that become more optically thick as they heat accelerate $\sim\! 35{{\ \rm per\ cent}}$ faster than clouds that become optically thin. An enhancement of $\sim\! 85{{\ \rm per\ cent}}$ in the acceleration can be achieved by having a broken power-law opacity profile, which allows the evaporating gas driving the cloud to become optically thin and not attenuate the driving radiation flux. We find that up to $\sim\! 2{{\ \rm per\ cent}}$ of incident radiation is re-emitted by accelerating clouds, which we estimate as the contribution of a single accelerating cloud to an emission or absorption line. Re-emission is suppressed by ‘bumps’ in the opacity–temperature relation since these decrease the opacity of the hot, evaporating gas, primarily responsible for the reradiation. If clouds are optically thin, they heat nearly uniformly, expand and form shocks. This triggers the Richtmyer–Meshkov instability, leading to cloud disruption and dissipation on thermal time-scales. Our work shows that, for some parameters, the rocket effect due to radiation-ablated matter leaving the back of the cloud is important for cloud acceleration. We suggest that this rocket effect can be at work in active galactic nuclei outflows.

scholarly journals Dynamical Evolution of Accretion Flow onto a Black Hole

1998 ◽  
Vol 188 ◽  
pp. 455-456
Author(s):  
M. Yokosawa
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Event Horizon ◽  
Accretion Disk ◽  
Dynamical Evolution ◽  
Galactic Nuclei ◽  
Thick Disk ◽  
X Ray ◽  
General Relativistic ◽  
Inner Region

Active galactic nuclei(AGN) produce many type of active phenomena, powerful X-ray emission, UV hump, narrow beam ejection, gamma-ray emission. Energy of these phenomena is thought to be brought out binding energy between a black hole and surrounding matter. What condition around a black hole produces many type of active phenomena? We investigated dynamical evolution of accretion flow onto a black hole by using a general-relativistic, hydrodynamic code which contains a viscosity based on the alpha-model. We find three types of flow's pattern, depending on thickness of accretion disk. In a case of the thin disk with a thickness less than the radius of the event horizon at the vicinity of a marginally stable orbit, the accreting flow through a surface of the marginally stable orbit becomes thinner due to additional cooling caused by a general-relativistic Roche-lobe overflow and horizontal advection of heat. An accretion disk with a middle thickness, 2rh≤h≤ 3rh, divides into two flows: the upper region of the accreting flow expands into the atmosphere of the black hole, and the inner region of the flow becomes thinner, smoothly accreting onto the black hole. The expansion of the flow generates a dynamically violent structure around the event horizon. The kinetic energy of the violent motion becomes equivalent to the thermal energy of the accreting disk. The shock heating due to violent motion produces a thermally driven wind which flows through the atmosphere above the accretion disk. A very thick disk, 4rh≤h,forms a narrow beam whose energy is largely supplied from hot region generated by shock wave. The accretion flowing through the thick disk,h≥ 2rh, cannot only form a single, laminar flow falling into the black hole, but also produces turbulent-like structure above the event horizon. The middle disk may possibly emit the X-ray radiation observed in active galactic nuclei. The thin disk may produce UV hump of Seyfert galaxy. Thick disk may produce a jet observed in radio galaxy. The thickness of the disk is determined by accretion rate, such ashκ κes/cṁf(r) κ 10rhṁf(r), at the inner region of the disk where the radiation pressure dominates over the gas pressure. Here, Ṁ is the accretion rate and ṁ is the normarized one by the critical-mass flux of the Eddington limit. κesandcare the opacity by electron scattering and the velocity of light.f(r) is a function with a value of unity far from the hole.

scholarly journals Line-driven disc wind in near-Eddington active galactic nuclei: decrease of mass accretion rate due to powerful outflow

2020 ◽  
Vol 494 (3) ◽  
pp. 3616-3626 ◽  
Author(s):  
Mariko Nomura ◽  
Ken Ohsuga ◽  
Chris Done
Keyword(s):  
Black Holes ◽  
Mass Loss ◽  
Active Galactic Nuclei ◽  
Accretion Rate ◽  
Galactic Nuclei ◽  
Host Galaxy ◽  
Radiation Hydrodynamics ◽  
Iterative Technique ◽  
X Ray ◽  
Mass Accretion Rate

ABSTRACT Based on recent X-ray observations, ultrafast outflows from supermassive black holes are expected to have enough energy to dramatically affect their host galaxy but their launch and acceleration mechanisms are not well understood. We perform two-dimensional radiation hydrodynamics simulations of UV line-driven disc winds in order to calculate the mass-loss rates and kinetic power in these models. We develop a new iterative technique that reduces the mass accretion rate through the inner disc in response to the wind mass-loss. This makes the inner disc less UV bright, reducing the wind power compared to previous simulations which assumed a constant accretion rate with radius. The line-driven winds in our simulations are still extremely powerful, with around half the supplied mass accretion rate being ejected in the wind for black holes with mass 108–$10^{10}\, \mathrm{ M}_\odot$ accreting at L/LEdd = 0.5–0.9. Our results open up the way for estimating the growth rate of supermassive black hole and evaluating the kinetic energy ejected into the interstellar medium (active galactic nuclei feedback) based on a physical model of line-driven disc winds.

scholarly journals Q wind code release: a non-hydrodynamical approach to modelling line-driven winds in active galactic nuclei

2020 ◽  
Vol 495 (1) ◽  
pp. 402-412
Author(s):  
Arnau Quera-Bofarull ◽  
Chris Done ◽  
Cedric Lacey ◽  
Jonathan C McDowell ◽  
Guido Risaliti ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Spectral Energy Distribution ◽  
Galactic Nuclei ◽  
Spectral Energy ◽  
Complex Nature ◽  
Radiation Hydrodynamics ◽  
Black Hole Mass ◽  
Acceleration Phase ◽  
Robust Algorithms ◽  
Hydrodynamical Simulations

ABSTRACT Ultraviolet (UV) line-driven winds may be an important part of the active galactic nucleus (AGN) feedback process, but understanding their impact is hindered by the complex nature of the radiation hydrodynamics. Instead, we have taken the approach pioneered by Risaliti & Elvis, calculating only ballistic trajectories from radiation forces and gravity but neglecting gas pressure. We have completely rewritten their Qwind code using more robust algorithms and can now quickly model the acceleration phase of these winds for any AGN spectral energy distribution spanning UV and X-ray wavebands. We demonstrate the code using an AGN with black hole mass $10^8\, \text{M}_\odot$ emitting at half the Eddington rate and show that this can effectively eject a wind with velocities ${\simeq}(0.1-0.2)\, c$. The mass loss rates can be up to ≃0.3M⊙ per year, consistent with more computationally expensive hydrodynamical simulations, though we highlight the importance of future improvements in radiation transfer along the multiple different lines of sight illuminating the wind. The code is fully public and can be used to quickly explore the conditions under which AGN feedback can be dominated by accretion disc winds.

scholarly journals Numerical study of an X-ray-driven carbon foil

1991 ◽  
Vol 9 (3) ◽  
pp. 759-768 ◽  
Author(s):  
N. W. Kaiser ◽  
J. Meyer-Ter-Vehn ◽  
R. Ramis
Keyword(s):  
Radiation Flux ◽  
Numerical Study ◽  
Wave Model ◽  
Incident Radiation ◽  
Carbon Layer ◽  
Radiation Hydrodynamics ◽  
Radiation Model ◽  
Thin Carbon ◽  
Carbon Plasma ◽  
Heat Front

The radiation hydrodynamics of a 125-μm thin carbon layer illuminated by thermal radiation of Trad = 200 eV temperature is studied within a multigroup radiation model. Whereas a major part of the incident photons deposit their energy by K-shell absorption close to the surface, soft photons below the K edge and hard photons (hv > 800 eV) penetrate deeper into the material and drive a heat wave with a sharp front. A nonablated mass fraction of 20% is accelerated with a hydrodynamic efficiency of 11%. About half of the incident radiation flux is reemitted by the heated carbon plasma. The heat front trajectory can be reproduced by the analytical heating wave model when effective opacity parameters corresponding to the most penetrating components are used.

scholarly journals Tracking the state transitions in changing-look active galactic nuclei through their polarized-light echoes

2020 ◽  
Vol 636 ◽  
pp. A23 ◽  
Author(s):  
F. Marin ◽  
D. Hutsemékers
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Rate ◽  
Rapid Change ◽  
Polarized Light ◽  
Galactic Nuclei ◽  
Time Dependent ◽  
Host Galaxy ◽  
State Transitions ◽  
Light Echoes ◽  
Dependent Polarization

Context. Variations in the mass accretion rate appear to be responsible for the rapid transitions in spectral type that are observed in increasingly more active galactic nuclei (AGNs). These objects are now labeled “changing-look” AGNs and are key objects for understanding the physics of accretion onto supermassive black holes. Aims. We aim to complement the analysis and interpretation of changing-look AGNs by modeling the polarization variations that can be observed, in particular, polarized-light echoes. Methods. We built a complex and representative model of an AGN and its host galaxy and ran radiative transfer simulations to obtain realistic time-dependent polarization signatures of changing-look objects. Based on actual data, we allowed the system to become several times fainter or brighter within a few years, assuming a rapid change in accretion rate. Results. We obtain time-dependent polarization signatures of distant high-luminosity (quasars) and nearby low-luminosity (Seyferts) changing-look AGNs for a representative set of inclinations. We predict the evolution of the continuum polarization for future polarimetric campaigns with the goal to better understand the physics at work in these objects. We also investigate highly inclined AGNs that experience strong accretion rate variations without appearing to change state. We apply our modeling to Mrk 1018, the best-documented case of a changing-look AGN, and predict a variation in its polarization after the recent dimming of its continuum. Conclusions. We demonstrate that polarization monitoring campaigns that cover the transitions that are observed in changing-look AGNs might bring crucial information on the geometry and composition of all the reprocessing regions within the nucleus. In particular, specific features in the time variation of the polarization position angle can provide a new and efficient method for determining AGN inclinations.

scholarly journals Radiation Hydrodynamics Models of Active Galactic Nuclei: Beyond the Central Parsec

2020 ◽  
Vol 897 (1) ◽  
pp. 26
Author(s):  
David Williamson ◽  
Sebastian Hönig ◽  
Marta Venanzi
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Radiation Hydrodynamics ◽  
Central Parsec

scholarly journals Tracing the Physical Conditions in Active Galactic Nuclei with Time-Dependent Chemistry

2013 ◽  
Vol 117 (39) ◽  
pp. 9593-9604 ◽  
Author(s):  
Rowin Meijerink ◽  
Marco Spaans ◽  
Inga Kamp ◽  
Giambattista Aresu ◽  
Wing-Fai Thi ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Time Dependent ◽  
Physical Conditions
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