Radio galaxies with linear sizes exceeding 1.5 Mpc
form the class of giant radio galaxies (GRGs, Saripalli et al., 1986).
Their radio luminosities seem
to lie in a range ( W Hz
), just
above the transition that distiguishes powerful FRII sources from the
low luminosity FRI sources (Fanaroff and Riley 1974). Their optical spectra are
observed only to have narrow emission lines.
The aim of studying this class of object is twofold. First, since
their radio properties are so extreme, they are an ideal laboratory
for studying the physics of radio sources. Are they so extreme in
size because of a low density environment, a high jet power or high
age?. Second, these are the only radio sources that probe inter
galaxy medium (IGM) over such a large scale. Studying these sources
will therefore constrain the structure of the IGM.
At the moment the Westerbork Northern Sky Survey (WENSS) is being
carried out. It will cover the whole sky north of 20 degrees
declination to a (5) flux limit of about 25 mJy at 327 MHz,
and will contain some 300,000 radio sources. This catalogue will
enable many types of radio sources to be selected and studied more
than one order of magnitude deeper in flux density than hitherto was
possible.
This low-frequency radio survey will
enable many types of radio sources to be selected at about an order of
magnitude deeper in flux density than hitherto was possible.
Studies of giants have been significantly hampered since the known samples are not well defined and contain only a dozen or so objects. Because of its good sensitivity at a low frequency to low surface brightness features at scales of a few minutes, the WENSS survey will provide a well defined and relatively large sample of giant radio galaxies. In this letter we report the discovery of a giant from the first WENSS data.