Giant radio sources

Abstract

A B S T R A C TWe present multifrequency Very Large Array (VLA) observations of two giant quasars, 04372244 and 10252229, from the Molonglo Complete Sample. These sources have welldefined FR II radio structure, possible one-sided jets, no significant depolarization between 1365 and 4935 MHz and low rotation measure jRMj , 20 rad m 22 . The giant sources are defined to be those with overall projected size >1 Mpc. We have compiled a sample of about 50 known giant radio sources from the literature, and have compared some of their properties with a complete sample of 3CR radio sources of smaller sizes to investigate the evolution of giant sources, and test their consistency with the unified scheme for radio galaxies and quasars. We find an inverse correlation between the degree of core prominence and total radio luminosity, and show that the giant radio sources have similar core strengths to smaller sources of similar total luminosity. Hence their large sizes are unlikely to be caused by stronger nuclear activity. The degree of collinearity of the giant sources is also similar to that of the sample of smaller sources. The luminosity±size diagram shows that the giant sources are less luminous than our sample of smaller sized 3CR sources, consistent with evolutionary scenarios in which the giants have evolved from the smaller sources, losing energy as they expand to these large dimensions. For the smaller sources, radiative losses resulting from synchrotron radiation are more significant while for the giant sources the equipartition magnetic fields are smaller and inverse Compton loss owing to microwave background radiation is the dominant process. The radio properties of the giant radio galaxies and quasars are consistent with the unified scheme.

Low-frequency study of two giant radio galaxies: 3C 35 and 3C 223

“…In the complete sample of 3CR radio sources (Laing et al 1983) around 6% of the sources are giants; there are about 100 known. Giant radio galaxies typically have radio powers below 10 26.5 W Hz −1 sr −1 , have linear sizes less than 3 Mpc, and are observed at redshifts z < 0.25, even though z < 0.5 could be assumed as an upper limit (Ishwara-Chandra & Saikia 1999;Schoenmakers et al 2000;Lara et al 2004;Saripalli et al 2005;Machalski et al 2007). The P-D diagram (Lara et al 2004;Ishwara-Chandra & Saikia 1999) shows a dearth of high luminosity GRG, as predicted by evolutionary models (Blundell et al 1999;) and a maximum GRG linear size cut-off of 3 Mpc.…”

“…Giant radio galaxies typically have radio powers below 10 26.5 W Hz −1 sr −1 , have linear sizes less than 3 Mpc, and are observed at redshifts z < 0.25, even though z < 0.5 could be assumed as an upper limit (Ishwara-Chandra & Saikia 1999;Schoenmakers et al 2000;Lara et al 2004;Saripalli et al 2005;Machalski et al 2007). The P-D diagram (Lara et al 2004;Ishwara-Chandra & Saikia 1999) shows a dearth of high luminosity GRG, as predicted by evolutionary models (Blundell et al 1999;) and a maximum GRG linear size cut-off of 3 Mpc. An estimate of the predominant process of radiative losses, obtained by separating the contributions of the inverse Compton and synchrotron losses, shows that the ratio of the estimated B CMB /B eq increases with linear size, and IC losses dominate the radiative losses in GRG (Ishwara-Chandra & Saikia 1999).…”

A Search for Giant Radio Galaxy Candidates and Their Radio-Optical Follow-up

“…Statistical analyses of samples of GRGs [9,10] suggest that their extreme sizes neither can be explained by a preferred orientation in the plane of the sky, nor by a location in less dense regions of the Universe, nor by more powerful jets feeding their lobes and thus reaching further out in intergalactic space. Instead, [10] argued that it is an exceptionally long-lasting radio activity in ∼10 % of FR II sources [8] that allows GRGs to develop.…”

“…Nac. de Astrofíca,Óptica y Electrónica, Tonantzintla, Pue., Mexico e-mail: ericja@inaoep.mx I. Plauchu-Frayn Instituto de Astronomía, UNAM, Ensenada, B.C., Mexico e-mail: ilse@astrosen.unam.mx E. Momjian NRAO, Socorro, NM 87801, USA e-mail: emomjian@nrao.edu cles published prior to our study (e.g., [9,11,15,12]), homogenising the data to H 0 = 75 km s −1 Mpc −1 , we compiled a list of only 100 GRGs.…”

IGR J17488–2338: a newly discovered giant radio galaxy

“…Some of them are characterised by giant structures and are known as giant radio galaxies (GRGs), formally those with linear sizes larger than 0.7 Mpc (e.g. Lara et al 2001;Ishwara-Chandra & Saikia 1999, scaled for the cosmology adopted here of H 0 = 71 km s −1 Mpc −1 , Ω m = 0.27, Ω Λ = 0.73). These objects represent the largest and most energetic single entities in the Universe and it is possible that they play a special role in the formation of large-scale structures.…”