Portal de Periódicos da CAPES

The radio galaxy IC 4296 (PKS 1333 - 33). III - Interpretation of the radio, optical, and X-ray data

1988; IOP Publishing; Volume: 324; Linguagem: Inglês

10.1086/165890

1538-4357

N. E. B. Killeen, G. V. Bicknell,

Galaxies: Formation, Evolution, Phenomena

view Abstract Citations (28) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Radio Galaxy IC 4296 (PKS 1333-33). III. Interpretation of the Radio, Optical, and X-Ray Data Killeen, N. E. B. ; Bicknell, G. V. Abstract Extensive observations of the radio galaxy IC 4296 (PKS 1333-33) have been reported in two previous papers. Killeen, Bicknell, and Ekers described multifrequency VLA observations, while Killeen, Bicknell, and Carter discussed optical and X-ray data. In this paper we discuss the interpretation of these data. The antiparallel radio jets of PKS 1333-33 are initially of low surface brightness (at 3.2" resolution), unresolved, light (with respect to the ISM), and supersonic. In the range 5" <~ {THETA} <~ 60" (0.9-10.3 kpc for H_0_ = 100 km s^-1^ Mpc^-^1, {THETA} is the angular distance from the core) each jet contains a train of knots. These knots appear to be oblique shocks caused either by initially free jets becoming confined or by a sudden decrease in the confining external pressure at approximately a core radius. At {THETA} <~ 15" (2.6 kpc) the jets begin to widen rapidly. This is because of the decreasing external pressure and also probably a widening turbulent boundary layer. As the jets widen, they brighten substantially and the initially steep spectral index flattens. We surmise that the jets "turn on" in this fashion because of a combination of shock-induced particle acceleration at the knots and subsequent stochastic particle acceleration. As the jets widen rapidly, the Mach number increases, suppressing the growth of the turbulently spreading boundary layer and causing a transition to laminar flow which is completed by {THETA} ~ 60" (10.3 kpc). It is this transition together with the variation of the external pressure that cause the slowing in the spreading rate at {THETA} ~ 35" (6 kpc). In the region 60" <~ {THETA} <~ 110" (10.3-18.8 kpc), the jets are well described by adiabatic, laminar flow. However, by {THETA} ~ 110" (18.8 kpc) the external pressure begins to flatten, and this causes the jets to turbulently entrain again and decelerate. The resultant compression of the jet plasma and magnetic field and probably some dissipation causes the surface brightness to decrease more slowly than for a constant velocity adiabatic jet. It is also in this region that lateral oscillations become appreciable and the linear, helical Kelvin-Helmholtz instability possibly provides an acceptable model. Alternatively, the jets may buckle because of the compressional stress associated with deceleration. By the time the jets form the lobes (~170 kpc from the core), they are probably still mildly supersonic, or transonic. An analysis of the energy budget shows that if the source is ~10^8^ yr old, then the velocities of the jets may be as high as 20,000 km s^-1^ at {THETA} ~ 20" (3.4 kpc). At larger {THETA}, velocities of ~5000 km s^-1^ are more likely. Decreasing the age increases the deduced velocities, and if the source is ~10^7^ yr old, then mildly relativistic velocities are possible. The large-scale curvature of the source is consistent with a model in which the motion of IC 4296 with respect to the cluster IGM induces a pressure gradient in the ISM causing the jets to bend. Soon after the point where we observe the jets to initially widen, the projected magnetic field changes from its initial longitudinal configuration to one that is transverse. At this point ({THETA} ~18" = 3.1 kpc) the degree of polarization (P) reaches its minimum. As the jets widen, P increases smoothly, reaching a plateau at {THETA} ~60" where P ~ 0.4. This behavior and the minimum (a result also of beam depolarization) can be accounted for by a simple model in which the magnetic field consists of isolated thin islands and in which the number of field lines is conserved. The degree of polarization is determined by the ratio of the perpendicular to parallel components of the magnetic field which increases as the jets widen. Publication: The Astrophysical Journal Pub Date: January 1988 DOI: 10.1086/165890 Bibcode: 1988ApJ...324..198K Keywords: Astronomical Spectroscopy; Radio Galaxies; Radio Sources (Astronomy); Spectrum Analysis; Visible Spectrum; X Ray Spectra; Astronomical Models; Kelvin-Helmholtz Instability; Mach Number; Polarization Characteristics; Radio Jets (Astronomy); Astrophysics; GALAXIES: INDIVIDUAL ALPHANUMERIC: IC 4296; GALAXIES: INDIVIDUAL ALPHANUMERIC: PKS 1333-33; GALAXIES: JETS; GALAXIES: X-RAYS; RADIO SOURCES: GALAXIES full text sources ADS | data products SIMBAD (1) NED (1) Related Materials (2) Part 1: 1986ApJ...302..306K Part 2: 1986ApJ...309...45K