We report the discovery of the largest giant radio galaxy , J1420-0545 : a FR type II radio source with an angular size of 17.4 ’ identified with an optical galaxy at z =0.3067 .
Thus , the projected linear size of the radio structure is 4.69 Mpc ( if we assume that H _ { 0 } =71 km s ^ { -1 } Mpc ^ { -1 } , \Omega _ { m } =0.27 , and \Omega _ { \Lambda } =0.73 ) .
This makes it larger than 3C236 , which is the largest double radio source known to date .
New radio observations with the 100 m Effelsberg telescope and the Giant Metrewave Radio Telescope , as well as optical identification with a host galaxy and its optical spectroscopy with the William Herschel Telescope are reported .
The spectrum of J1420 - 0545 is typical of elliptical galaxies in which continuum emission with the characteristic 4000 Å discontinuity and the H and K absorption lines are dominated by evolved stars .
The dynamical age of the source , its jets ’ power , the energy density , and the equipartition magnetic field are calculated and compared with the corresponding parameters of other giant and normal-sized radio galaxies from a comparison sample .
The source is characterized by the exceptionally low density of the surrounding IGM and an unexpectedly high expansion speed of the source along the jet axis .
All of these may suggest a large inhomogeneity of the IGM .