J1420−0545: The Radio Galaxy Larger than 3C 236

Abstract

We report the discovery of the largest giant radio galaxy yet, J1420À0545: a FR type II radio source with an angular size of 17.4 0 , identified with an optical galaxy at z ¼ 0:3067. Thus, the projected linear size of the radio structure is 4.69 Mpc (if we assume that H 0 ¼ 71 km s À1 Mpc À1 , m ¼ 0:27, and à ¼ 0:73). This makes it larger than 3C 236, 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 J1420À0545 is typical of elliptical galaxies in which continuum emission with the characteristic 4000 8 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.

The circumnuclear cold gas environments of the powerful radio galaxies 3C 236 and 4C 31.04

“…The Mpc-scale structure -making 3C 236 one of the two largest single objects in the universe (e.g. Schilizzi et al 2001;Machalski et al 2008) -is not imaged in our VLBA observations.…”

LOFAR discovery of a 700-kpc remnant radio galaxy at low redshift

“…The jets of relativistic particles produced by the AGN can reach distances of up to a few Mpc from the host galaxy (Willis et al 1974;Machalski et al 2008). The active phase of the radio AGN can last several tens of Myr, after which the nuclear activity stops and the source starts to fade away (Parma et al 1999).…”

Reassessment of an Origin of the Radio Structure of J1420–0545

“…To sum up, in this paper, we test the possibility that the structure of the largest radio galaxy, J1420−0545, discovered by Machalski et al (2008), may be formed by restarted, rather than primary, jet activity. As mentioned in Section 1, this hypothesis was motivated by the unusual morphological properties of the source, suggesting an almost ballistic propagation of powerful jets in a particularly low-density ambient medium.…”

“…8), having an angular size of 17. 4, was discovered by Machalski et al (2008). Its weak radio core coincides with a parent galaxy at a spectroscopic redshift of 0.3067 (presented in their paper).…”

“…Machalski et al 2008Machalski et al , 2011Machalski et al , 2016, the modeling procedure performed in this paper uses the DYNAGE algorithm of Machalski et al (2007). This numerical code allows the determination, for a given set of observables, of the four main , and the DYNAGE model fit to the residual data points originated within the low-frequency range of the spectrum from the GLEAM survey (the dashed line).…”