Nature and evolution of powerful radio galaxies at z ∼ 1 and their link with the quasar luminosity function

Abstract

Current wide-area radio surveys are dominated by active galactic nuclei, yet many of these sources have no identified optical counterparts. Here we investigate whether one can constrain the nature and properties of these sources, using Fanaroff-Riley type II (FR II) radio galaxies as probes. These sources are easy to identify since the angular separation of their lobes remains almost constant at some tens of arcseconds for z > 1. Using a simple algorithm applied to the FIRST survey, we obtain the largest FR II sample to date, containing over 10 4 double-lobed sources. A subset of 459 sources is matched to SDSS quasars. This sample yields a statistically meaningful description of the fraction of quasars with lobes as a function of redshift and luminosity. This relation is combined with the bolometric quasar luminosity function, as derived from surveys at IR to hard X-ray frequencies, and a disc-lobe correlation to obtain a robust prediction for the density of FR IIs on the radio sky. We find that the observed density can be explained by the population of known quasars, implying that the majority of powerful jets originate from a radiatively efficient accretion flow with a linear jet-disc coupling. Finally, we show that high-redshift jets are more often quenched within 100 kpc, suggesting a higher efficiency of jet-induced feedback into their host galaxies.

CMB quenching of high-redshift radio-loud AGNs

“…It turns out that at z ≃ 4 the mean cosmic density is comparable to the typical density of the intra-cluster medium ≃ 1 Mpc away from the center of a typical formed cluster at z ∼ < 1. Because of this coincidence, we then expect that the lobe sizes of high-redshift blazars are not very different from those of very powerful radio sources residing in low-z virialized clusters (although some additional effect may cause the apparent lack of hot spots and lobes at distances larger than 100 kpc for FR II radio-galaxies at z ∼ > 1 found by van Velzen, Falcke & Körding 2015).…”

On the efficiency of jet production in FR II radio galaxies and quasars

“…Recent studies of the jet powers in a sample of radio selected FR II quasars by van Velzen & Falcke (2013) (see also van Velzen et al 2015) show that the median jet production efficiency in these objects is tens times lower than maximal predicted by the MAD scenario. Such low jet production efficiency in the MAD scenario would require very low median BH spin and this led the authors to conclude that jet production in these systems does not involve magnetically arrested discs.…”

Covering factors of the dusty obscurers in radio-loud and radio-quiet quasars

“…A large catalogue of 59192 FR II radio sources (Fanaroff & Riley 1974) was recently compiled by van Velzen et al (2015), using data from the Faint Images of the Radio Sky at Twentycentimetres (FIRST) catalogue (Becker et al 1995). From this, van Velzen et al (2015) selected a sample of 1108 FR II quasars by matching their FR II radio sources with the combined DR7 and DR9 catalogues of SDSS quasars.…”

“…From this, van Velzen et al (2015) selected a sample of 1108 FR II quasars by matching their FR II radio sources with the combined DR7 and DR9 catalogues of SDSS quasars. We are interested only in the DR7 quasars, for which black hole mass estimates are available (Shen et al 2011).…”

“…We are interested only in the DR7 quasars, for which black hole mass estimates are available (Shen et al 2011). Since sources that are both in the DR7 and DR9 are denoted as 'DR9', in order to select all DR7 quasars, we performed additional matching of the FR II quasar sample of van Velzen et al (2015) (1108 sources) with the SDSS DR7 quasar catalogue (Schneider et al 2010) (105783 sources). We used a matching radius of 5 arcsec and obtained 899 objects.…”