M. Jamrozy

Spectral ageing analysis of the double–double radio galaxy J1453+3308

We present new radio observations at frequencies ranging from 240 to 4860 MHz of the well-known, double-double radio galaxy (DDRG), J1453+3308, using both the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA). These observations enable us to determine the spectra of the inner and outer lobes over a large frequency range and demonstrate that while the spectrum of the outer lobes exhibits significant curvature, that of the inner lobes appears practically straight. The break frequency, and hence the inferred synchrotron age of the outer structure, determined from 16-arcsec strips transverse to the source axis, increases with distance from the heads of the lobes. The maximum spectral ages for the northern and southern lobes are ∼47 and 58 Myr, respectively. Because of the difference in the lengths of the lobes, these ages imply a mean separation velocity of the heads of the lobes from the emitting plasma of 0.036c for both the northern and southern lobes. The synchrotron age of the inner double is about 2 Myr which implies an advance velocity of ∼0. 1c, but these values have large uncertainties because the spectrum is practically straight.

A multifrequency study of giant radio sources – II. Spectral ageing analysis of the lobes of selected sources

Multifrequency observations with the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA) are used to determine the spectral breaks in consecutive strips along the lobes of a sample of selected giant radio sources (GRSs) in order to estimate their spectral ages. The maximum spectral ages estimated for the detected radio emission in the lobes of our sources range from ∼6 to 46 Myr with a median value of ∼23 Myr using the classical equipartition fields. Using the magnetic field estimates from the Beck & Krause formalism the spectral ages range from ∼5 to 58 Myr with a median value of ∼24 Myr. These ages are significantly older than smaller sources. In all but one source (J1313+6937) the spectral age gradually increases with distance from the hotspot regions, confirming that acceleration of the particles mainly occurs in the hotspots. Most of the GRSs do not exhibit zero spectral ages in the hotspots, as is the case in earlier studies of smaller sources. This is likely to be largely due to contamination by more extended emission due to relatively modest resolutions. The injection spectral indices range from ∼0.55 to 0.88 with a median value of ∼0.6. We discuss these values in the light of theoretical expectations, and show that the injection spectral index appears to be correlated with luminosity and/or redshift as well as with linear size.

The new sample of giant radio sources: I. radio imaging, optical identification and spectroscopy of selected candidates

A new sample of very large angular size radio sources has been selected from the 1.4 GHz VLA surveys: FIRST and NVSS. This sample will be very useful for an observational constraint on the time evolution of double radio sources, especially their size, predicted by numerous analytical models of such evolution (cf. Introduction). In this paper we present radio and optical data for a large fraction of the sample sources. They are: high-frequency VLA maps with very weak radio cores detected, deep optical images showing the identified faint host galaxies not visible on the DSS images, and optical spectra of the identified galaxies brighter than about

A multifrequency study of giant radio sources – I. Low-frequency Giant Metrewave Radio Telescope observations of selected sources

R\approx 18.5

Intermittent jet activity in the radio galaxy 4C 29.30

mag taken with the McDonald Observatory 2.1 m telescope. For 15 galaxies (of which 4 do not belong to the complete sample) the redshift has been determined. In the result, 44 per cent of galaxies in the complete sample have redshift data (with one exception all redshifts are less than 0.33), of which 70 per cent have a linear size exceeding 1 Mpc. The photometric redshift estimates for other 11 galaxies with

A multifrequency study of giant radio sources – III. Dynamical age versus spectral age of the lobes of selected sources

19 {\rm mag}< R< 21.7

Episodic radio galaxies J0116 4722 and J1158+2621: can we constrain the quiescent phase of nuclear activity?

mag (

Multi-wavelength environment of the Galactic globular cluster Terzan 5

0.3< z< 0.5

The peculiar radio galaxy 4C 35.06: a case for recurrent AGN activity?

) predict their sizes much over 1 Mpc.

UNDERSTANDING GIANT RADIO GALAXY J1420–0545: LARGE-SCALE MORPHOLOGY, ENVIRONMENT, AND ENERGETICS

We present low-frequency observations with the Giant Metrewave Radio Telescope of a sample of giant radio sources, and high-frequency observations of three of these sources with the Very Large Array. From multifrequency observations of the lobes, we estimate the magnetic field strengths using three different approaches, and show that these differ at most by a factor of ∼3. For these large radio sources, the inverse-Compton losses usually dominate over synchrotron losses when estimates of the classical minimum energy magnetic field are used, consistent with earlier studies. However, this is often not true if the magnetic fields are close to the values estimated using the formalism of Beck & Krause. We also examine the spectral indices of the cores and any evidence of recurrent activity in these sources. We probe the environment using the symmetry parameters of these sources and suggest that their environments are often asymmetric on scales of ∼1 Mpc, consistent with earlier studies.