2006/11/20 by M. H. Cohen, M. L. Lister, D. C. Homan +4 · 6 citations
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #Radio Astronomy Observations and Technology #astro-ph
paper · pdf · doi:10.1086/511063
published as Astrophys.J.658:232-244,2007 · 12 pages, 9 figures, 1 table, accepted for publication in the Astrophysical Journal
arxiv created 2006/11/20 · openalex publication_date 2007/03/14 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
Relations between the observed quantities for a beamed radio jet, which are the apparent transverse speed and the apparent luminosity (β app , L ), and the intrinsic quantities, which are the Lorentz factor and the intrinsic luminosity (γ, L 0 ), are investigated. The inversion from measured to intrinsic values is not unique, but approximate limits to γ and L 0 can be found using probability arguments. Roughly half the sources in a flux density-limited, beamed sample have a value of γ close to the measured value of β app . The methods are applied to observations of 119 AGN jets made with the VLBA at 15 GHz during 1994-2002. The results strongly support the common relativistic beam model for an extragalactic radio jet. The (β app , L ) data are closely bounded by a theoretical envelope, an "aspect" curve for γ = 32 and L 0 = 10 25 W Hz -1 . This gives limits to the maximum values of γ and L 0 in the sample: γ max ≈ 32, and L 0,max ~ 10 26 W Hz -1 . No sources with both high values of β app and low values of L are observed. This is not the result of selection effects due to the observing limits, which are a flux density of S > 0.5 Jy and an angular velocity of μ < 4 mas yr -1 . Many of the fastest quasars have a pattern Lorentz factor, γ p , that is close to that of the beam, γ b , but some of the slow quasars must have γ p ≪ γ b . Three of the 10 galaxies in the sample have a superluminal feature, with speeds up to β app ≈ 6. The others are at most mildly relativistic. The galaxies are not off-axis versions of the powerful quasars, but Cygnus A might be an exception.