Shadowing of the Nascent Jet in NGC 4261 by a Line‐emitting Supersonic Accretion Disk

Abstract

NGC 4261 (3C 270) is a low-luminosity radio galaxy with two symmetric kiloparsec-scale jets. Earlier Hubble Space Telescope observations indicated the presence of a hundred-parsec scale disk of cool dust and gas surrounding a central, supermassive (∼ 4.9 × 10 8 M ⊙ ) black hole. The recent detection of free-free radio absorption by a small, geometrically-thin disk, combined with earlier studies of the disk's large scale properties, provide the strictest constraints to date on the nature of the accretion process in this system. We show here that a supersonic disk, illuminated by the active galactic nucleus (AGN), can not only account for the observed radio shadowing, but can also produce the optical broad lines emitted from this region. At large radii, the gas is optically-thin because the ram pressure due to turbulence is much larger than the thermal pressure of the gas. At smaller radii, but beyond a critical radius r c , line cooling dominates over gravitational dissipation and the gas is effectively cooled down to temperatures below 10 4 K. Within r c , however, heating due to 1 NSF Graduate Fellow.2 Sir Thomas Lyle Fellow and Miegunyah Fellow.-2the release of gravitational energy overwhelms line cooling and the gas falls onto the unstable portion of the cooling curve. Because cooling is quite inefficient under these conditions, the plasma is heated very quickly to a temperature close to its virial value as it falls toward the central engine. Thermal pressure of the gas dominates the turbulent ram pressure at a radius ∼ (2/3) r c , below which the flow probably becomes advection dominated. The disk is optically-thin to UV and X-ray radiation within r c , so the ionizing radiation from the AGN is preferentially absorbed near r c , affecting the disk structure significantly. To include the ensuing photoionization effect, we have used the algorithm Cloudy with additional heating introduced by gravitational dissipation to calculate the temperature profile and line emission from the disk in a self-consistent manner.The results of our model calculation are consistent with current multiwavelength observations of the disk in this source.

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

“…In a similar case of NGC 6251, Sudou et al (2000) have already pointed out such difficulties as appeared above in interpreting the emission gap in terms of the free-free absorption by a radiation cooled disk of any type. Also for similar reasons, Liu et al (2003) have presented an alternative interpretation of this phenomenon.…”

Gravitational Waves Produced by Ejection of Jet Superluminal Components, Precession and Gravito-Magnetic Distortion of Accretion Disks in Active Galactic Nuclei, Micro-Quasars, and T-Tauri Stars Dynamically Driven by Bardeen-Petterson Effect

“…Indeed, according to Ref. [13] a similar physics seems to dominate the source Sgr A * , which is said to harbour a SMBH-torus system in the center of our Galaxy. In the case of Sgr A * , the rise time for flaring should vary from half of, to at least a few times, the period of the vertical oscillations.…”

Kinetic theory of quasi-stationary collisionless axisymmetric plasmas in the presence of strong rotation phenomena

“…Supersonic flows can naturally be expected to arise in the presence of strong gravity close to Kerr black holes and naked singularities, where possibility of ultrarelativistic motion relative to the space-time in the locally non-rotating frames 14,15 indicates existence of relativistic bulk flow velocities and strong rotation phenomena in both accretion discs 16 and spherical accretion. 17 However, it is interesting to notice that such ultrarelativistic motion may appear to be very slow relative to distant observers, if it occurs in the ergosphere.…”