Radio-loudness of active galaxies and the black hole evolution

Abstract

Active galactic nuclei (AGNs) form two distinct sequences on the radio-loudness -Eddington-ratio plane. The 'upper' sequence contains radio selected AGNs, the 'lower' sequence is composed mainly of optically selected AGNs. The sequences mark the upper bounds for the radio-loudness of two distinct populations of AGNs, hosted respectively by elliptical and disk galaxies. Both sequences show the same dependence of the radio-loudness on the Eddington ratio (an increase with decreasing Eddington ratio), which suggests that another parameter in addition to the accretion rate must play a role in determining the efficiency of jet production in AGNs. We speculate that this additional parameter is the spin of the black hole, assuming that black holes in giant elliptical galaxies have (on average) much larger spins than black holes in disc galaxies. Possible evolutionary scenarios leading to such a spin dichotomy are discussed. The galaxy-morphology related radio-dichotomy breaks down at high accretion rates where the dominant fraction of luminous quasars being hosted by giant ellipticals is radio quiet. This indicates that the production of powerful jets at high accretion rates is in most cases suppressed and, in analogy to X-ray binary systems (XRB) during high and very high states, may be intermittent. Such intermittency can be caused by switches between two different accretion modes, assuming that only during one of them an outflow from the central engine is sufficiently collimated to form a relativistic jet.

Fr Ii Quasars: Infrared Properties, Star Formation Rates, and Extended Ionized Gas

“…There are substantial reasons for believing that radio-loud quasars, at least at low redshifts, are drawn from a population of massive elliptical galaxies that may have suffered mergers in the fairly recent past, while many radio-quiet QSOs are found either in disk galaxies or in ongoing gas-rich mergers (Sikora et al 2007(Sikora et al , 2008Wolf & Sheinis 2008). We can test this explanation by looking at the PG QSOs in the Schweitzer et al (2006) sample that also have morphological determinations by Guyon et al (2006) or elsewhere in the literature.…”

The Dynamics and Energetics of Remnant and Restarting RLAGN

“…Restarted activity is likely to be a normal part of the active radio lifecycle of massive ellipticals; thus, in the first instance, the central black hole and accretion properties that drive jet activity must be related to their modulation. There have been suggestions for quasars with the highest accretion rates that intermittency is favoured in elliptical galaxies (e.g., [119,120]), or that stochastic development of poloidal magnetic fields in the accretion disks lead to intermittent jets [121,122]; nevertheless it is likely that episodic activity is intimately related to the activity of the accretion system in both quasars and non-quasars. Several mechanisms have been discussed to explain accretion disturbances, such as thermal instabilities [123], the infall of large gas clouds to the centre of the galaxy as a consequence of mergers [90], and intermittent jet collimation by accretion disk winds [124]; however, there is insufficient observational evidence for these processes occurring in restarting RLAGN as a population.…”

MERLIN and EVN observations of a z=4.515 radio galaxy, RC J0311+0507, and the problem of SMBHs in the early Universe

“…Multi-component radio structures for low luminosity objects can usually be explained by irregular "cooling flows" or by "large molecular cloud" accretions [15]. High luminosity RGs with complex structures and high BH masses could result from mergers of cluster galaxies or from collisions between two SMBHs, see [21,22]. However, for young, multi-component, very powerful radio galaxies, the usual "multi-merging" explanation seems difficult because of the short time scale for nuclear events -smaller than the free-fall time or galaxy rotation period.…”