Evidence for a maximum jet efficiency for the most powerful radio galaxies

Abstract

The definitive version can be found at: http://www.wiley.com/ Copyright Wiley BlackwellWe use new mid-infrared (mid-IR) photometry from the Spitzer Space Telescope to study the relations between low-frequency radio luminosity density L-nu 151 (MHz), mid-IR (12 mu m rest frame) luminosity nu L-nu 12 (mu m) and optical emission-line ([O II]) luminosity L-[O II], for a complete sample of z similar to 1 radio galaxies from the 3CRR, 6CE, 6C*, 7CRS and TOOT00 surveys. The narrow redshift span of our sample (0.9 < z < 1.1) means that it is unbiased to evolutionary effects. We find evidence that these three quantities are positively correlated. The scaling between nu L-nu 12 (mu m) and L-[O II] is similar to that seen in other active galactic nuclei samples, consistent with both nu L-nu 12 (mu m) and L-[O II] tracing accretion rate. We show that the positive correlation between nu L-nu 12 (mu m) and L-nu 151 (MHz) implies that there is a genuine lack of objects with low values of nu L-nu 12 (mu m) at high values of L-nu 151 (MHz). Given that nu L-nu 12 (mu m) traces accretion rate, while L-nu 151 (MHz) traces jet power, this can be understood in terms of a minimum accretion rate being necessary to produce a given jet power. This implies that there is a maximum efficiency with which accreted energy can be chanelled into jet power and this efficiency is of the order of unity

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

“…These studies demonstrated that magnetically arrested discs have the ability to launch jets with a power comparable to the accretion power, as is required to explain the energetics of radio lobes in the radioloudest FR II sources (Rawlings & Saunders 1991;Punsly 2007;Fernandes et al 2011;.…”

“…Table A3. Properties from the Table 1 in Fernandes et al (2011) and Table 3 in Fernandes et al (2015) with added log P j and log P j /L d values. …”

“…With a few exceptions, they all have FR II radio morphologies. The relevant data for this sample are presented in the Table A3, which are taken from Table 1 in Fernandes et al (2011), as well as Table 3 in Fernandes et al (2015). As before, Pj is calculated based on Equation 2.…”

“…Jet production theories are challenged not only by the large spread of radio-loudness, but also by the fact that the jet powers in many radio galaxies reach values comparable to the accretion powers (Rawlings & Saunders 1991;Punsly 2007;Fernandes et al 2011;. In order to produce jets with such high efficiency in the BlandfordZnajek mechanism (Blandford & Znajek 1977), BHs are required not only to be spinning very fast but also to be threaded by a very large magnetic flux.…”

Probing the radio loud/quiet AGN dichotomy with quasar clustering

“…How these jets form is still a matter of debate and their physics is not yet completely understood. Several factors such as accretion rate (Lin et al 2010;Fernandes et al 2011), BH spin (Blandford & Znajek 1977;Sikora et al 2007;Fernandes et al 2011;van Velzen & Falcke 2013), BH mass (Laor 2000;Dunlop et al 2003;Chiaberge & Marconi 2011), and quasar environment (Fan et al 2001;Ramos Almeida et al 2013), but most probably a combination of them, may be responsible for the conversion of accreted material into well-collimated jets. This division into RLQs and RQQs still remains a point of discussion.…”