Are seyfert narrow-line regions powered by radio jets?

Geoffrey V. Bicknell, Michael A. Dopita, Zlatan I. Tsvetanov, Ralph S. Sutherland

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Abstract

We argue that the narrow-line regions (NLRs) of Seyfert galaxies are powered by the transport of energy and momentum by the radio-emitting jets. This implies that the ratio of the radio power to jet energy flux is much smaller than is usually assumed for radio galaxies. This can be partially attributed to the smaller ages (∼106 yr) of Seyferts compared to radio galaxies, but one also requires that either the magnetic energy density is more than 1 order of magnitude below the equipartition value or, more likely, that the internal energy densities of Seyfert jets are dominated by thermal plasma, as distinct from the situation in radio galaxy jets where the jet plasma is generally taken to be nonthermally dominated. If one assumes that the internal energy densities of Seyfert jets are initially dominated by relativistic plasma, then an analysis of the data on jets in five Seyfert galaxies shows that all but one of these would have mildly relativistic jet velocities near 100 pc in order to power the respective narrow-line regions. However, observations of jet-cloud interactions in the NLR provide additional information on jet velocities and composition via the momentum budget. Our analysis of a jet-cloud interaction in NGC 1068, 24 pc from the core implies a shocked jet pressure much larger than the minimum pressure of the radio knot, a velocity (probably accurate to within a factor of a few) ∼0.06c (18,000 km s-1), and a temperature of thermal gas in the jet ∼109 K, implying mildly relativistic electrons but thermal protons. The estimated jets velocity is proportional to the jet energy flux and provides an independent argument that the energy flux in the northern NGC 1068 jet is much greater than previously supposed and is capable of providing significant energy input to the narrow line region. The jet mass flux at this point ∼0.5 M yr-1, is 1 oder of magnitude higher than the mass accretion rate ∼0.05 M yr-1 estimated from the bolometric luminosity of the nucleus, strongly indicating entrainment into the jet and accompanying deceleration. Consequently, the jet velocity near the black hole is possibly mildly relativistic. We estimate an initial jet mass flux ∼0.02 M yr-1 which is comparable to the mass accretion rate. This mass flux is consistent with the densities inferred for accretion disk coronae from high energy observations, together with an initially mildly relativistic velocity and an initial jet radius of order 10 gravitational radii.

Original languageEnglish
Pages (from-to)680-690
Number of pages11
JournalAstrophysical Journal
Volume495
Issue number2 PART I
DOIs
Publication statusPublished - 1 Jan 1998

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Keywords

  • Galaxies: Jets
  • Galaxies: Seyfert

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Bicknell, G. V., Dopita, M. A., Tsvetanov, Z. I., & Sutherland, R. S. (1998). Are seyfert narrow-line regions powered by radio jets? Astrophysical Journal, 495(2 PART I), 680-690. https://doi.org/10.1086/305336