Giant Radio Galaxies - old long-living quasars?
  Based on the miscellaneous published radio and optical data, SDSS and APM
catalogue we consider the various properties of the giant radio sources (gRS)
with the aim of refining the conditions leading to the formation of these
objects. We compare gRSs with the regular-sized radio sources in radio and
optical bands, yielding the following results: 1. The fraction of broad line
objects among gRSs with high excitation spectrum is the same as for the RSs
from isotropic samples. According to Unified Scheme this leads to the isotropic
angle distribution of gRSs jets, thus gRSs cannot be characterized as objects
with jets lying in the plane of sky. 2. gRSs do not differ from normal sized
RSs in apparent asymmetry distribution of their extended radio components
(ERC). However the fact that asymmetry distributions for gRSs and giant radio
quasars (gQSS) are essentially the same leads within the Unification Scheme to
the conclusion that the origin of this asymmetry is in the non-uniform
environment. 3. The richness of the environment for gRSs is the same as for
normal sized RSs. This contradicts the opinion that the low density of the
environment is the single reason for gRSs formation. 4. About 10% of FRII RSs
have by order of magnitude longer lifetimes and eventually evolve to gRSs. 5.
The observed relative quantity of radio quasars in gRSs population (~0.1) can
be interpreted as the presence of long-living population of radio loud QSSs as
~0.1 of all radio quasars.
