Accretion and jet power in active galactic nuclei
📝 Abstract
The classical diagrams of radio loudness and jet power as a function of mass and accretion rate of the central spacetime singularity in active galactic nuclei are reanalyzed by including the data of the recently discovered powerful relativistic jets in Narrow-Line Seyfert 1 Galaxies. The results are studied in the light of the known theories on the relativistic jets, indicating that while the Blandford-Znajek mechanism is sufficient to explain the power radiated by BL Lac Objects, it fails to completely account the power from quasars and Narrow-Line Seyfert 1. This favors the scenario outlined by Cavaliere & D’Elia of a composite jet, with a magnetospheric core plus a hydromagnetic component emerging as the accretion power increases and the disc becomes radiation-pressure dominated. A comparison with Galactic compact objects is also performed, finding some striking similarities, indicating that as the neutron stars are the low-mass jet systems analogue of black holes, the Narrow-Line Seyfert 1 Galaxies are the low-mass counterpart of the blazars.
💡 Analysis
The classical diagrams of radio loudness and jet power as a function of mass and accretion rate of the central spacetime singularity in active galactic nuclei are reanalyzed by including the data of the recently discovered powerful relativistic jets in Narrow-Line Seyfert 1 Galaxies. The results are studied in the light of the known theories on the relativistic jets, indicating that while the Blandford-Znajek mechanism is sufficient to explain the power radiated by BL Lac Objects, it fails to completely account the power from quasars and Narrow-Line Seyfert 1. This favors the scenario outlined by Cavaliere & D’Elia of a composite jet, with a magnetospheric core plus a hydromagnetic component emerging as the accretion power increases and the disc becomes radiation-pressure dominated. A comparison with Galactic compact objects is also performed, finding some striking similarities, indicating that as the neutron stars are the low-mass jet systems analogue of black holes, the Narrow-Line Seyfert 1 Galaxies are the low-mass counterpart of the blazars.
📄 Content
arXiv:1106.5532v2 [astro-ph.HE] 24 Aug 2011 Research in Astron. Astrophys. Vol.0 (200x) No.0, 000–000 http://www.raa-journal.org http://www.iop.org/journals/raa Research in Astronomy and Astrophysics Accretion and jet power in active galactic nuclei L. Foschini INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807, Merate (LC), Italy; luigi.foschini@brera.inaf.it Abstract The classical diagrams of radio loudness and jet power as a function of mass and accretion rate of the central spacetime singularity in active galactic nuclei are reana- lyzed by including the data of the recently discovered powerful relativistic jets in Narrow- Line Seyfert 1 Galaxies. The results are studied in the light of the known theories on the relativistic jets, indicating that while the Blandford-Znajek mechanism is sufficient to ex- plain the power radiated by BL Lac Objects, it fails to completely account the power from quasars and Narrow-Line Seyfert 1. This favors the scenario outlined by Cavaliere & D’Elia of a composite jet, with a magnetospheric core plus a hydromagnetic compo- nent emerging as the accretion power increases and the disc becomes radiation-pressure dominated. A comparison with Galactic compact objects is also performed, finding some striking similarities, indicating that as the neutron stars are the low-mass jet systems ana- logue of black holes, the Narrow-Line Seyfert 1 Galaxies are the low-mass counterpart of the blazars. Key words: galaxies: jets – BL Lacertae objects: general – quasars: general – galaxies: Seyfert 1 INTRODUCTION Despite their omnipresence in the Universe and thousands of written papers, relativistic jets are still poorly understood and there is not yet consensus on the mechanisms at work. In the discussion after the Blandford’s seminal talk at the 1978 “Pittsburgh conference on BL Lac Objects”, G. Burbidge raised one question about the possible importance of the host galaxy in the generation of relativistic jets in BL Lacs. Blandford answered that the host galaxy should not be a relevant detail, because the phenomena related to the jet occur within the central ten parsecs (Blandford & Rees 1978). However, later observations seemed to support the idea that instead the host galaxy plays some role, with jets preferring ellipticals rather than spirals. By inverting the Blandford’s answer, Laor (2000) asked how is it possible that the jet, which indeed is originated in the very inner part of a galaxy, could be related to the host. He suggested that one possible solution is that jets require large black hole masses (≳109M⊙), which in turn are hosted in ellipticals. On the other hand, AGN with no jets have masses of the central singularity ≲3 × 108M⊙. Sikora et al. (2007) confirmed some similar division, although with smoother boundaries, by finding that AGN with M ≳108M⊙have the radio loudness parameters 3 orders of magnitudes greater than those AGN with M ≲3 × 107M⊙. Sikora et al. (2007) reported also about some differences between the radio loudness and accretion rate of the central black hole in spiral- and elliptical-hosted AGN, where just a very few exceptions of spiral-hosted AGN can display high accretion and high radio loudness. Generally, the radio loudness is greater as the accretion rate is lower, somehow recalling the jets in Galactic binaries, which are linked to low/hard states (see Belloni 2010 for recent reviews). 2 L. Foschini Recently, Broderick & Fender (2011) suggested a correction of the radio loudness due to the mass, which determines the vanishing of the radio-loud/quiet dichotomy and leaving only a general trend of a greater radio loudness as the accretion rate decreases. Last, but not least, when speaking about jets, the black hole spin cannot be missing. It is like it has “a finger in every pie” (“come il prezzemolo”, in Italian saying), with its contribution mixed in every possible way. This scenario has been perturbed by the recent discovery of high-energy γ rays from Narrow-Line Seyfert 1 Galaxies (γ-NLS1s, see Foschini 2011a for a recent review1). These AGN have relatively small masses (106−8M⊙), high accretion rate (0.1−1LEdd, see Fig. 8 in Foschini 2011a), are generally hosted by spiral galaxies, and could develop powerful relativistic jets, as luminous as those in blazars. Other differences with blazars refer to the full width half maximum (FWHM) of the broad permitted lines (in the case of Hβ, the value is ≳2000 km/s for blazars and ≲2000 km/s for γ-NLS1s) and the radio morphology, which is very compact (≲10 pc, see e.g. Gu & Chen 2010, except one known case, PKS 0558-504, Gliozzi et al. 2010) for γ-NLS1s, while blazars display extended structures, up to hundreds of parsecs. Therefore, even though the jets of γ-NLS1s are very similar to those in blazars, almost all the remaining part of the AGN and the host galaxy are different, meaning that γ-NLS1s are indeed a new class of γ-ray AGN(2). In the present work, I report on a comparative study of the ma
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