What Kinds of Accretion Disks Are There in the Nuclei of Radio Galaxies?

Kaburaki, Osamu; Nankou, Takanobu; Tamura, Naoya; Wajima, Kiyoaki

doi:10.1093/pasj/62.5.1177

Cited by 9 publications

(12 citation statements)

References 45 publications

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“…When considering the low-excitation sources, it is evident that NGC 315 is not the only object showing a subparsec scale transition, which is observed also in other two lowluminosity jets, NGC 1052 and NGC 4261. At least in the case of NGC 4261, this distance is also much smaller than the Bondi radius, estimated by Balmaverde et al (2008) to be ∼32 pc, but it may match the actual extent of the hot gas phase as inferred from a spectral fitting performed by Kaburaki et al (2010). None of the jets in HEG presents a sub-parsec scale transition, and the transition distances seem to be shifted to larger radii than in LEG.…”

Section: Transition Distancementioning

confidence: 63%

Jet collimation in NGC 315 and other nearby AGN

Boccardi

Perucho

Casadio

et al. 2021

A&A

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Aims. The collimation of relativistic jets in galaxies is a poorly understood process. Detailed radio studies of the jet collimation region have been performed so far in a few individual objects, providing important constraints for jet formation models. However, the extent of the collimation zone as well as the nature of the external medium possibly confining the jet are still debated. Methods. In this article, we present a multifrequency and multiscale analysis of the radio galaxy NGC 315, including the use of mm-VLBI data up to 86 GHz, aimed at revealing the evolution of the jet collimation profile. We then consider results from the literature to compare the jet expansion profile in a sample of 27 low-redshift sources, mainly comprising radio galaxies and BL Lacs, which were classified based on the accretion properties as low-excitation (LEG) and high-excitation (HEG) galaxies. Results. We propose that the jet collimation in NGC 315 is completed on sub-parsec scales. A transition from a parabolic to conical jet shape is detected at zt = 0.58 ± 0.28 parsecs or ∼5 × 103 Schwarzschild radii (RS) from the central engine, a distance which is much smaller than the Bondi radius, rB ∼ 92 pc, estimated based on X-ray data. The jet in this and in a few other LEG in our sample may be initially confined by a thick disk extending out to ∼103 − 104RS. A comparison between the mass-scaled jet expansion profiles of all sources indicates that jets in HEG are surrounded by thicker disk-launched sheaths and collimate on larger scales with respect to jets in LEG. These results suggest that disk winds play an important role in the jet collimation mechanism, particularly in high-luminosity sources. The impact of winds on the origin of the FRI and FRII dichotomy in radio galaxies is also discussed.

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Section: Transition Distancementioning

confidence: 63%

Jet collimation in NGC 315 and other nearby AGN

Boccardi

Perucho

Casadio

et al. 2021

A&A

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“…The importance of magnetic diffusivity has been studied in several accreting systems, such as protostellar discs (Stone et al 2000; Fleming & Stone 2003), discs in dwarf nova systems (Gammie & Menou 1998), the discs around black holes (Kudoh & Kaburaki 1996) and the Galactic Centre (Melia & Kowalenkov 2001; Kaburaki et al 2010). Moreover, two‐ and three‐dimensional magnetohydrodynamics (MHD) simulations have shown that resistive dissipation is one of the crucial processes that determine the saturation amplitude of the magnetorotational instability (MRI).…”

Section: Introductionmentioning

confidence: 99%

Viscous and resistive accretion flows with radially self-similar outflows

Faghei¹,

Mollatayefeh²

2012

Monthly Notices of the Royal Astronomical Society

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The existence of outflows in accretion flows has been confirmed by observations and by magnetohydrodynamics simulations. In this paper, we study the outflows of advection-dominated accretion flows (ADAFs) in the presence of resistivity and a toroidal magnetic field. The mechanism of energy dissipation in the flow is assumed to be the viscosity and the magnetic diffusivity as a result of turbulence in the accretion flow. It is also assumed that the magnetic diffusivity and the kinematic viscosity are not constant and that they vary by position, and the α-prescription is used for these. The influence of outflows emanating from an accretion disc is considered as a sink for mass, angular momentum and energy. The self-similar method is used to solve the integrated equations that govern the behaviour of the accretion flow in the presence of outflows. The solutions represent the disc that rotates faster and becomes cooler for stronger outflows. Moreover, by adding magnetic diffusivity, the surface density and rotational velocity decrease, while the radial velocity and temperature increase. A study of the present model with the magnitude of a magnetic field implies that the disc rotates and accretes faster and becomes hotter, while the surface density decreases. The thickness of the disc increases when adding a magnetic field or resistivity, while the disc becomes thinner for more mass and energy losses resulting from the outflows.

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“…The resistive diffusion of magnetic field is important in some systems, such as the protostellar discs Fleming & Stone 2003), discs in dwarf nova systems (Gammie & Menou 1998), the discs around black holes (Kudoh & Kaburaki 1996), and Galactic center (Melia & Kowalenkov 2001;Kaburaki et al 2010). Also, two and three dimensional simulations of local shearing box have shown that resistive dissipation is one of the crucial processes that determines the saturation amplitude of the magnetorotational instability (MRI).…”

Section: Introductionmentioning

confidence: 99%

“…However, recent works represent importance of magnetic diffusivity in accretion discs (e.g. Kuwabara et al 2000;Kaburaki 2000 ;Kaburaki et al 2002;Sh04;Ghanbari et al 2007;Krasnopolsky et al 2010;Kaburaki et al 2010). Sh04 studied a quasi-spherical accretion flow that dominant mechanism of energy dissipation was assumed to be the magnetic diffusivity due to turbulence in the accretion flow and the viscosity of the fluid was completely neglected.…”

Section: Introductionmentioning

confidence: 99%

Self-Similar Solutions for Viscous and Resistive Advection Dominated Accretion Flows

Faghei

2012

J Astrophys Astron

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Abstract.In this paper, the self-similar solution of resistive advection dominated accretion flows (ADAF) in the presence of a pure azimuthal magnetic field is investigated. The mechanism of energy dissipation is assumed to be the viscosity and the magnetic diffusivity due to turbulence in the accretion flow. It is assumed that the magnetic diffusivity and the kinematic viscosity are not constant and vary by position and α-prescription is used for them. In order to solve the integrated equations that govern the behavior of the accretion flow, a self-similar method is used. The solutions show that the structure of accretion flow depends on the magnetic field and the magnetic diffusivity. As, the radial infall velocity and the temperature of the flow increase, and the rotational velocity decreases. Also, the rotational velocity for all selected values of magnetic diffusivity and magnetic field is sub-Keplerian. The solutions show that there is a certain amount of magnetic field that the rotational velocity of the flow becomes zero. This amount of the magnetic field depends on the gas properties of the disc, such as adiabatic index and viscosity, magnetic diffusivity, and advection parameters. The solutions show the mass accretion rate increases by adding the magnetic diffusivity and in high magnetic pressure case, the ratio of the mass accretion rate to the Bondi accretion rate decreases as magnetic field increases. Also, the study of Lundquist and magnetic Reynolds numbers based on resistivity indicates that the linear growth of magnetorotational instability (MRI) of the flow decreases by resistivity. This property is qualitatively consistent with resistive magnetohydrodynamics (MHD) simulations.

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What Kinds of Accretion Disks Are There in the Nuclei of Radio Galaxies?

Cited by 9 publications

References 45 publications

Jet collimation in NGC 315 and other nearby AGN

Jet collimation in NGC 315 and other nearby AGN

Viscous and resistive accretion flows with radially self-similar outflows

Self-Similar Solutions for Viscous and Resistive Advection Dominated Accretion Flows

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