H. van der Laan

A new sample of giant radio galaxies from the WENSS survey - II. A multi-frequency radio study of a complete sample: Properties of the radio lobes and their environment

We have formed a complete sample of 26 low redshift (z less than or similar to 0.3) giant radio galaxies (GRGs) from the WENSS survey, selected at flux densities above 1 Jy at 325 MHz. We present 10.5-GHz observations with the 100-m Effelsberg telescope of 18 sources in this sample. These observations, together with similar data of the remaining eight sources, are combined with data from the WENSS, NVSS and GB6 surveys to study the radio properties of the lobes of these sources at arcminute resolution. We investigate radio source asymmetries, equipartition energy densities in the lobes, the presence of lobe pressure evolution with redshift, the spectral age and the density of the environments of these sources. We iind that the arm length asymmetries of GRGs are slightly larger than those of smaller sized 3CR radio galaxies and that these are difficult to explain as arising from orientation effects only. We also find indications that the lobes of the GRGs, despite their large sizes, are still overpressured with respect to their environment. Further, we argue that any evolution of lobe pressure with redshift in these large sources (e.g. Cotter 1998) is due to selection effects. For sources which could be used in a spectral ageing analysis, we find spectral ages which are large, typically a few times 10(7) Sr. This is comparable to earlier studies of some giant sources and indicates that such large spectral ages are common for this class of radio source. The advance velocities of the radio lobes are typically a few percent of the speed of light; which is higher than those found for smaller, low power (<10(26.5) W Hz(-1) at 178 MHz) radio sources, and more comparable to higher power radio sources. This suggests that the GRGs in our sample are the oldest members of the group of relatively high power radio sources whose radio powers have evolved to their currently observed lower values (cf. Kaiser et al. 1997).

Radio galaxies with a ‘double‐double’ morphology – III. The case of B 1834+620

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

Radio Galaxies: the z-Dependence of their Proper Densities and Colours

\sim\!2

Towards a Complete Sample of Giant Radio Galaxies at Z > 0.4

rad m

Radio galaxies with a ‘double-double morphology’- I. Analysis of the radio properties and evidence for interrupted activity in active galactic nuclei

^{-2}

A new sample of giant radio galaxies from the WENSS survey. I. Sample definition, selection effects and first results

of 58 rad m

Expanding Supernova Remnants and Galactic Radio Sources

^{-2}

Intense Shell Sources of Radio Emission

. 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

A new sample of giant radio galaxies from the WENSS survey

\la 1.6 \times 10^{-30}

A first 1415MHz survey with the Westerbork Synthesis Radio Telescope : an attempt to detect radio emission from quasi stellar objects.

gr\,cm