Spectral ageing analysis and dynamical analysis of the double-double radio galaxy J1548–3216

Abstract

Context. Determining ages of the outer and the inner lobes of so-called double-double radio galaxies (DDRGs) is crucial for understanding the active cycles of galactic nuclei, the phases of interruption of the jet flow, and physical conditions in the surrounding galactic and intergalactic medium governing the jets' propagation. A recognition and understanding of these conditions during the restarted jet activity is of special interest. Aims. We determine the ages and other physical characteristics of the outer and the inner lobes of the DDRG J1548−3216, as well as the properties of the surrounding environment during the original and the restarted phase of the jets' activity. Methods. Using the new low-frequency and high-frequency radio images of this galaxy, we determined the shape of the spectrum along its lobes and performed the classical spectral-ageing analysis. On the other hand, we applied the analytical model of the jet's dynamics, which allowed us to derive the physical conditions for the source's evolution during the original jet propagation through the unperturbed IGM, as well as those when the restarted new jet propagates inside the outer cocoon formed by the old jet material that passed through the jet terminal shock. Results. The dynamical age estimate of the outer and the inner lobes is 132 ± 28 Myr and ∼9 ± 4 Myr, respectively. The synchrotron age in the outer lobes systematically rises from ∼25 Myr in the vicinity of the lobes' edges to about 65-75 Myr in the centre of the old cocoon. These ages imply an average expansion speed along the jets' axis: (0.012 ± 0.003)c in the outer lobes and (0.058 ± 0.025)c in the inner lobes, but the latter speed would be ∼0.25 c when they were of age less than 1 Myr. We find that the jet power during the restarted activity is about ten-fold fainter than that of the original jet. Similar disproportion is found for the internal pressures and the magnetic field strengths in the old cocoon and those in the inner lobes. This disproportion can be effectively reduced by assuming the same equations of state for the emitting particles and the magnetic fields within the old and the new lobes. However, we think that our assumption of the non-relativistic equation of state for the old cocoon and the relativistic one for the new lobes is more justified.

Evidence for a significant mixture of electron/positron pairs in FRII jets constrained by cocoon dynamics

“…By comparing the revised cocoon model with the actually observed morphology of the cocoons, we have already suggested the method of dynamical constraint on P tot c (Kino & Kawakatu 2005;I08). Note that the reliability of the expanding cocoon model was well examined in Kawakatu and Kino (2006), was supported by the results of relativistic hydrodynamical simulations (Scheck et al 2002;Perucho & Marti 2007;Mizuta et al 2010) and was applied to various radio lobes (e.g., Machalski et al 2010).…”

A dynamical model for FR II type radio sources with terminated jet activity

“…Its dynamical analysis was published by Safouris et al (2008) concluding that the interruption of the jet activity was brief, no more than a small percent of the actual age of the whole source. Nevertheless, based on new low-frequency observations with the GMRT array, Machalski et al (2010) has repeated the dynamical age analysis but applied to the opposite lobes in both the outer and the inner pairs. The source location on the southern sky hemisphere means that it is not covered by the large radio surveys on the northern sky: VLSS, NVSS, FIRST, WENSS.…”

Dynamical analysis of the complex radio structure in 3C 293: clues on a rapid jet realignment in X-shaped radio galaxies

“…We note that, for the ambient medium at > 1 kpc distances from the active nucleus, we anticipate the standard King profile with a given core radius a 0 and a slope β. As in our previous works (Machalski et al 2010(Machalski et al , 2011, the modelling is performed using the DYNAGE algorithm of et al (2007). This numerical code enables us to solve the inverse problem, i.e., to determine the above four free parameters (Q j , t lb , p, and ρ 0 ) by fitting the model to a given set of observables, including the linear size and the volume of the lobes, and the observed lobes' radio spectrum (i.e., the spectral power density at different observing frequencies).…”