Relativistic models and the jet velocity field in the radio galaxy 3C 31

By R. Laing, A. Bridle. 2002

159 citations recorded by the source corpus.

We compare deep Very Large Array (VLA) imaging of the total intensity and linear polarization of the inner jets in the nearby, low-luminosity radio galaxy 3C 31 with models of the jets as intrinsically symmetrical, decelerating relativistic flows. We show that the principal differences in appearance of the main and counter-jets within 30 arcsec of the nucleus can result entirely from the effects of relativistic aberration in two symmetrical, antiparallel, axisymmetric, time-stationary relativistic flows. We develop empirical parametrized models of the jet geometry and the three-dimensional distributions of the velocity, emissivity and magnetic-field structure. We calculate the synchrotron emission by integration through the models, accounting rigorously for relativistic effects and the anisotropy of emission in the rest frame. The model parameters are optimized by fitting to our 8.4-GHz VLA observations at resolutions of 0.25 and 0.75 arcsec full width at half maximum (FWHM), and the final quality of the fit is extremely good. The novel features of our analysis are that we model the two-dimensional brightness distributions at large number of independent data points rather than using one-dimensional profiles, we allow transverse as well as longitudinal variations of velocity, field and emissivity and we simultaneously fit total intensity and linear polarization. We conclude that the jets are ≈52° to the line of sight, that they decelerate and that they have transverse velocity gradients. Their magnetic field configuration has primarily toroidal and longitudinal components. The jets may be divided into three distinct parts, based not only on the geometry of their outer isophotes, but also on their kinematics and emissivity distributions: a well-collimated inner region; a flaring region of rapid expansion followed by recollimation and a conical outer region. The inner region is poorly resolved, but is best modelled as the sum of fast (0.8–0.9c) and much slower components. The transition between inner and flaring regions marks a discontinuity in the flow where the emissivity increases suddenly. The on-axis velocity stays fairly constant at ≈0.8c until the end of the flaring region, where it drops abruptly to ≈0.55c, thereafter falling more slowly to ≈0.25c at the end of the modelled region. Throughout the flaring and outer regions, the velocity at the edge of the jet is ≈0.7 of its on-axis value. The magnetic field in the flaring region is complex, with an essentially isotropic structure at the edge of the jet, but a more ordered toroidal + longitudinal configuration on-axis. In the outer region, the radial field vanishes and the toroidal component becomes dominant. We show that the emissivity and field structures are inconsistent with simple adiabatic models in the inner and flaring regions. We suggest that the discontinuity between the inner and flaring regions could be associated with a stationary shock structure and that the inferred transverse velocity profiles and field structure in the flaring region support the idea that the jets decelerate by entraining the external medium. We demonstrate the appearance of our model at other angles to the line of sight and argue that other low-luminosity radio galaxies resemble 3C 31 seen at different orientations.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/de57977f583eb27778c7d1abd16f96e937b20efc

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. Judith Croston
2. M. Hardcastle
3. E. Orlando
4. A. Strong
5. D. Harris
6. C. Jones
7. W. Forman
8. H. Krawczynski

In Nuclear and High Energy Physics

1. M. Hardcastle
2. Judith Croston
3. A. Strong
4. E. Orlando
5. D. Harris
6. H. Krawczynski
7. Y. Kovalev
8. D. Evans

Citations in the corpus

• FERMI DISCOVERY OF GAMMA-RAY EMISSION FROM NGC 1275 (2009, background): “…Ghisellini et al. 2005 for a spine-sheath velocity profile), as suggested by recent radio/X-ray observations (e.g., for transversal profiles, see Laing & Bridle 2002; Kataoka et al. 2006), it is possible to produce brightγ-ray emission from the nuclei of some radio galaxies via the inv rse…”
• X-Ray Emission from Extragalactic Jets (2006, background): “…circumstantial evidence for acceleration of jet features on pc-scales (e.g. Hardee, Walker & Gómez 2005) and it is generally accepted that both FRI (Laing & Bridle 2002a) and quasar (Wardle & Aaron 1997) jets decelerate on pc to kpc scales there is no indication that significant jet acceleration…”
• Hot and cold gas accretion and feedback in radio-loud active galaxies (2007, methodology): “For 3C 31 Laing & Bridle (2002b) quote a jet powerQ ≈ 1037 W.”
• Radio and X-Ray Observations of the Jet in Centaurus A (2003, methodology): “On the other hand, there is no particular reason to believe that theenergy density in the jet is the minimum energy, and some evidence that it is greater for FRI jets (e.g., Laing & Bridle 2002b) which would increase the required mass.”
• X-Ray Emission from the Hot Interstellar Medium and Southwest Radio Lobe of the Nearby Radio Galaxy Centaurus A (2003, background): “The jet/ lobe morphology of Cen A is clearly different than the ‘‘ tailed twin-jet ’’ morphology (Leahy 1993) commonly associated with objects like 3C 31 (Hardcastle et al. 2002b; Laing & Bridle 2002a, 2002b) and 3C 449 (Feretti et al. 1999).”
• A Chandra observation of the X-ray environment and jet of 3C 296 (2002, methodology): “3 and is associated with the well-collimated inner region defined by Laing & Bridle (2002a).”