On the radio dichotomy of active galactic nuclei

Abstract

It is still a mystery why only a small fraction of active galactic nuclei (AGNs) contain relativistic jets. Strong magnetic field is a necessary ingredient for jet formation, however, the advection of the external field in a geometrically thin disk is inefficient. The gas with a small angular velocity may fall from the Bondi radius $R_{\mathrm{B}}$ nearly freely to the circularization radius $R_{\mathrm{c}}$, and a thin accretion disk is formed within $R_{\mathrm{c}}$. We suggest that the external magnetic field is substantially enhanced in this region, and the magnetic field at $R_{\mathrm{c}}$ can be sufficiently strong to drive outflows from the disk if the angular velocity of the gas is low at $R_{\mathrm{B}}$. The magnetic field is efficiently dragged in the disk, because most angular momentum of the disk is removed by the outflows that leads to a significantly high radial velocity. The strong magnetic field formed in this way may accelerate jets in the region near the black hole either by the Blandford-Payne or/and Blandford-Znajek mechanisms. We suggest that the radio dichotomy of AGNs predominantly originates from the angular velocity of the circumnuclear gas. An AGN will appear as a radio-loud (RL) one if the angular velocity of the circumnuclear gas is lower than a critical value at the Bondi radius, otherwise, it will appear as a radio-quiet (RQ) AGN. This is supported by the observations that RL nuclei are invariably hosted by core galaxies. Our model suggests that the mass growth of the black holes in RL quasars is much faster than that in RQ quasars with the same luminosity, which is consistent with the fact that the massive black holes in RL quasars are systematically a few times heavier than those in their RQ counterparts.

accepted by ApJ, references updated

References in corpus (11)

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Cited by in corpus (9)

• Fundamental Plane of Black Hole Activity in Quiescent Regime
• Isothermal Bondi accretion in Jaffe and Hernquist galaxies with a central black hole: fully analytical solutions
• Jet Power of Jetted Active Galactic Nuclei: Implication for Evolution and Unification
• The power of the jets accelerated by the coronal magnetic field
• The radio dichotomy of active galactic nuclei
• Jets in the soft state in Cyg X-3 caused by advection of the donor magnetic field and unification with low-mass X-ray binaries
• Growth of massive black holes at high-z via accretion predominantly driven by magnetic outflows
• Powerful Radio Emission From Low-mass Supermassive Black Holes Favors Disk-like Bulges
• The dependence of the fraction of radio luminous quasars on redshift and its theoretical implications