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Astron. Astrophys. Suppl. Ser. 146, 293-322
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
A.P. Schoenmakers1,2,5
- K.-H. Mack3,4 - A.G. de Bruyn5,6 - H.J.A. Röttgering2 - U. Klein4 - H. van der Laan1
Send offprint request: A.P. Schoenmakers,
e-mail: schoenmakers@astron.nl
1 - Astronomical Institute, Utrecht University, P.O. Box 80000,
3508 TA Utrecht, The Netherlands
2 - Sterrewacht Leiden, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands
3 - Istituto di Radioastronomia del CNR, Via P. Gobetti 101, I-40129 Bologna, Italy
4 - Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
5 - NFRA, P.O. Box 2, 7990 AA Dwingeloo, The Netherlands
6 - Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, The Netherlands
Received December 15, 1999; accepted August 2, 2000
Abstract:
We have formed a complete sample of 26 low redshift (

)
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 find that the armlength
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 yr. 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).
Key words:
galaxies: active -- intergalactic medium -- galaxies: jets -- radio continuum: galaxies
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