AGN obscuration from winds: from dusty infrared-driven to warm and X-ray photoionized

We present calculations of AGN winds at ~parsec scales, along with the associated obscuration. We take into account the pressure of infrared radiation on dust grains and the interaction of X-rays from a central black hole with hot and cold plasma. Infrared radiation (IR) is incorporated in radiation-hydrodynamic simulations adopting the flux-limited diffusion approximation. We find that in the range of X-ray luminosities L=0.05 - 0.6 L_edd, the Compton-thick part of the flow (aka torus) has an opening angle of approximately 72-75 degrees regardless of the luminosity. At L > 0.1 L_edd the outflowing dusty wind provides the obscuration with IR pressure playing a major role. The global flow consists of two phases: the cold flow at inclinations \theta > 70 degrees and a hot, ionized wind of lower density at lower inclinations. The dynamical pressure of the hot wind is important in shaping the denser IR supported flow. At luminosities <0.1 L_edd episodes of outflow are followed by extended periods when the wind switches to slow accretion.Comment: accepted for publication in Ap

Active galaxy unification in the era of X-ray polarimetry

Active Galactic Nuclei (AGN), Seyfert galaxies and quasars, are powered by luminous accretion and often accompanied by winds which are powerful enough to affect the AGN mass budget, and whose observational appearance bears an imprint of processes which are happening within the central parsec around the black hole (BH). One example of such a wind is the partially ionized gas responsible for X-ray and UV absorption ('warm absorbers'). Here we show that such gas will have a distinct signature when viewed in polarized X-rays. Observations of such polarization can test models for the geometry of the flow, and the gas responsible for launching and collimating it. We present calculations which show that the polarization depends on the hydrodynamics of the flow, the quantum mechanics of resonance line scattering and the transfer of polarized X-ray light in the highly ionized moving gas. The results emphasize the three dimensional nature of the wind for modeling spectra. We show that the polarization in the 0.1-10 keV energy range is dominated by the effects of resonance lines. We predict a $5-25$ X-ray polarization signature of type-2 objects in this energy range. These results are general to flows which originate from a cold torus-like structure, located $\sim 1$pc from the BH, which wraps the BH and is ultimately responsible for the apparent dichotomy between type 1 and type 2 AGNs. Such signals will be detectable by future dedicated X-ray polarimetry space missions, such as the NASA Gravity and Extreme Magnetism SMEX, GEMS.Comment: 13 pages, 4 figures, ApJ Letters accepted for publicatio

Consequences of hot gas in the broad line region of active galactic nuclei

Models for hot gas in the broad line region of active galactic nuclei are discussed. The results of the two phase equilibrium models for confinement of broad line clouds by Compton heated gas are used to show that high luminosity quasars are expected to show Fe XXVI L alpha line absorption which will be observed with spectrometers such as those planned for the future X-ray spectroscopy experiments. Two phase equilibrium models also predict that the gas in the broad line clouds and the confining medium may be Compton thick. It is shown that the combined effects of Comptonization and photoabsorption can suppress both the broad emission lines and X-rays in the Einstein and HEAO-1 energy bands. The observed properties of such Compton thick active galaxies are expected to be similar to those of Seyfert 2 nuclei. The implications for polarization and variability are also discussed

Parsec-scale accretion and winds irradiated by a quasar

We present numerical simulations of properties of a parsec-scale torus exposed to illumination by the central black hole in an active galaxy (AGN). Our physical model allows to investigate the balance between the formation of winds and accretion simultaneously. Radiation-driven winds are allowed by taking into account radiation pressure due to UV and IR radiation along with X-ray heating and dust sublimation. Accretion is allowed through angular momentum transport and the solution of the equations of radiation hydrodynamics. Our methods adopt flux-limited diffusion radiation-hydrodynamics for the dusty, infrared pressure driven part of the flow, along with X-ray heating and cooling. Angular momentum transport in the accreting part of the flow is modeled using effective viscosity. Our results demonstrate that radiation pressure on dust can play an important role in shaping AGN obscuration. For example, when the luminosity illuminating the torus exceeds $L>0.01\,L_{\rm Edd}$, where $L_{\rm Edd}$ is the Eddington luminosity, we find no episodes of sustained disk accretion because radiation pressure does not allow a disk to form. Despite the absence of the disk accretion, the flow of gas to smaller radii still proceeds at a rate $10^{-4}-10^{-1}\,M_\odot\,{\rm yr}^{-1}$ through the capturing of the gas from the hot evaporative flow, thus providing a mechanism to deliver gas from a radiation-pressure dominated torus to the inner accretion disk. As $L/L_{\rm edd}$ increases, larger radiation input leads to larger torus aspect ratios and increased obscuration of the central black hole. We also find the important role of the X-ray heated gas in shaping of the obscuring torus.Comment: accepted to Ap

AGN Torus Threaded by Large Scale Magnetic Field

Large scale magnetic eld can be easily dragged from galactic scales towards AGN alongwith accreting gas. There, it can contribute to both the formation of AGN "torus" and help to remove angular momentum from the gas which fuels AGN accretion disk. Howeverthe dynamics of such gas is also strongly inuenced by the radiative feedback from theinner accretion disk. Here we present results from the three-dimensional simulations ofpc-scale accretion which is exposed to intense X-ray heating

An axisymmetric, hydrodynamical model for the torus wind in AGN

We report on time-dependent axisymmetric simulations of an X-ray excited flow from a parsec-scale, rotating, cold torus around an active galactic nucleus. Our simulations account for radiative heating and cooling and radiation pressure force. The simulations follow the development of a broad bi-conical outflow induced mainly by X-ray heating. We compute synthetic spectra predicted by our simulations. The wind characteristics and the spectra support the hypothesis that a rotationally supported torus can serve as the source of a wind which is responsible for the warm absorber gas observed in the X-ray spectra of many Seyfert galaxies.Comment: ApJ Letters, accepted for publicatio