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Register a new userThe inverse-Compton ghost HDF 130 and the giant radio galaxy 6C 0905+3955: matching an analytic model for double radio source evolution
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We present new GMRT observations of HDF 130, an inverse-Compton (IC) ghost of a giant radio source that is no longer being powered by jets. We compare the properties of HDF 130 with the new and important constraint of the upper limit of the radio flux density at 240 MHz to an analytic model. We learn what values of physical parameters in the model for the dynamics and evolution of the radio luminosity and X-ray luminosity (due to IC scattering of the cosmic microwave background (CMB)) of a Fanaroff-Riley II (FR II) source are able to describe a source with features (lobe length, axial ratio, X-ray luminosity, photon index and upper limit of radio luminosity) similar to the observations. HDF 130 is found to agree with the interpretation that it is an IC ghost of a powerful double-lobed radio source, and we are observing it at least a few Myr after jet activity (which lasted 5--100 Myr) has ceased. The minimum Lorentz factor of injected particles into the lobes from the hotspot is preferred to be $gammasim10^3$ for the model to describe the observed quantities well, assuming that the magnetic energy density, electron energy density, and lobe pressure at time of injection into the lobe are linked by constant factors according to a minimum energy argument, so that the minimum Lorentz factor is constrained by the lobe pressure. We also apply the model to match the features of 6C 0905+3955, a classical double FR II galaxy thought to have a low-energy cutoff of $gammasim10^4$ in the hotspot due to a lack of hotspot inverse-Compton X-ray emission. The models suggest that the low-energy cutoff in the hotspots of 6C 0905+3955 is $gammagtrsim 10^3$, just slightly above the particles required for X-ray emission.
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We present new XMM-Newton data of the high-redshift (z=1.883), Mpc-sized giant radio galaxy 6C 0905+39. The larger collecting area and longer observation time for our new data means that we can better characterise the extended X-ray emission, in particular its spectrum, which arises from cosmic microwave background photons scattered into the X-ray band by the energetic electrons in the spent synchrotron plasma of the (largely) radio-quiet lobes of 6C 0905+39. We calculate the energy that its jet-ejected plasma has dumped into its surroundings in the last 3 X 10^7 years and discuss the impact that similar, or even more extreme, examples of spent, radio-quiet lobes would have on their surroundings. Interestingly, there is an indication that the emission from the hotspots is softer than the rest of the extended emission and the core, implying it is due to synchrotron emission. We confirm our previous detection of the low-energy turnover in the eastern hotspot of 6C 0905+39.
Our XMM-Newton spectrum of the giant, high-redshift (z=1.88) radio galaxy 6C 0905+39 shows that it contains one of the most powerful, high-redshift, Compton-thick quasars known. Its spectrum is very hard above 2 keV. The steep XMM spectrum below that energy is shown to be due to extended emission from the radio bridge using Chandra data. The nucleus of 6C 0905+39 has a column density of 3.5 (+1.4,-0.4) X 10^24 cm^-2 and absorption-corrected X-ray luminosity of 1.7 (+0.9,-0.1) X 10^45 erg/s in the 2-10 keV band. A lower redshift active galaxy in the same field, SDSS J090808.36+394313.6, may also be Compton-thick.
Giant radio sources form the linear size extreme of the extra-galactic radio source population. Using the WENSS survey, we have selected a complete sample of these sources. We have investigated the properties of their radio structures. We find, among other things, that these sources are old (50-100 Myr) and have higher advance velocities than smaller sources of similar radio power. We find pressure gradients in their radio lobes, suggesting that the lobes are still overpressured with respect to the environment. Further, we find no evidence for a cosmological evolution of the radio lobe pressures with increasing redshift, at least up to $zsim 0.4$, other than that caused by selection effects. We argue that a much fainter sample of giant sources than currently available is needed to constrain the pressure in their environments, the IGM. Another extremely important discovery is that of a population of radio sources with a so-called `double-double structure, i.e. that of a small two-sided radio source embedded inside a much larger two-sided structure. We argue that these sources result from an interrupted central jet-forming activity. As such, they are the most convincing examples of radio sources with a history of interrupted activity, yet. Since the inner lobes advance within the outer lobes, high resolution low frequency ($sim 200$ MHz) polarization studies may reveal the constituents of radio lobes and cocoons. We thus argue for a SKA design that can provide low-frequency images at arcsec resolution, but which is also sensitive to structures as large as a few tens of arcminute on the sky.
There is compelling evidence showing that extragalactic jets are a crucial ingredient in the evolution of host galaxies and their environments. Extragalactic jets are well collimated and relativistic, both in terms of thermodynamics and kinematics at sub-parsec and parsec scales. They generate strong shocks in the ambient medium, associated with observed hotspots in FRII radio galaxies, and carve cavities that are filled with the shocked jet flow, dragging a large fraction of the interstellar gas along, in the form of slow, massive outflows within the host galaxies. In this paper, I discuss relevant processes associated to jet evolution in the frame of FRI-FRII dichotomy. In particular, I focus on the role of 1) the interaction between galactic atmospheres and the jet head on global FRII jet kinematics, and 2) mass load by stellar winds or small-scale instabilities on jet deceleration in FRI jets. The results presented are based on 3D relativistic hydrodynamical (RHD) and/or 2D axisymmetric, time-independent relativistic magnetohydrodynamical (RMHD) simulations.
We present a study of the peculiar radio galaxy B 1834+620. It is characterised by the presence of a 420-kpc large edge-brightened radio source which is situated within, and well aligned with, a larger (1.66 Mpc) radio source. Both sources apparently originate in the same host galaxy, which has a R_s-magnitude of 19.7 and a redshift of 0.5194, as determined from the strong emission-lines in the spectrum. We have determined the rotation measures towards this source, as well as the radio spectral energy distribution of its components. The radio spectrum of the large outer source is steeper than that of the smaller inner source. The radio core has a spectrum that peaks at a frequency of a few GHz. The rotation measures towards the four main components are quite similar, within $sim!2$ rad m$^{-2}$ of 58 rad m$^{-2}$. They are probably largely galactic in origin. We have used the presence of a bright hotspot in the northern outer lobe to constrain the advance velocity of the inner radio lobes to the range between 0.19c and 0.29c, depending on the orientation of the source. This corresponds to an age of this structure in the range between 2.6 and 5.8 Myr. We estimate a density of the ambient medium of the inner lobes of $la 1.6 times 10^{-30}$ gr,cm$^{-3}$ (particle density $la 8 times 10^{-7}$ cm$^{-3}$). A low ambient density is further supported by the discrepancy between the large optical emission-line luminosity of the host galaxy and the relatively low radio power of the inner lobes.
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