Discovery of a new, 2.2 Mpc Giant Radio Galaxy at a redshift of 0.57

TL;DR

This paper reports the discovery of a 2.2 Mpc giant radio galaxy at redshift 0.57, using GMRT and VLA data, with spectral aging analysis suggesting an age under 20 million years and evidence of multiple emission episodes.

Contribution

First discovery of such a large and distant giant radio galaxy at this redshift with detailed spectral aging and core analysis, indicating possible multiple activity episodes.

Findings

Linear size of 2.2 Mpc at redshift 0.57.

Spectral age estimated at less than 20 Myr.

Evidence for a second emission episode and a potential CSS core.

Abstract

We report the discovery of one of the largest and most distant Giant Radio Galaxy (GRG) in the Lynx field which was discovered using deep Giant Metre-wave Radio Telescope (GMRT) 150 MHz observations. The core is detected at 150 MHz and also in the VLA FIRST survey. Spectroscopic observations carried out using the IUCAA Giravali Observatory(IGO) provided a redshift value of 0.57. This redshift was later confirmed with data from the Sloan Digital Sky Survey (Data Release 12). The angular size of the GRG is 5.5 arcmin and at the redshift of 0.57, its linear size is 2.2 Mpc. At this high redshift, only a few radio sources are known to have such large linear size. In order to estimate the spectral index of the bridge emission as well as the spectral age of the source, we observed this source at L-band, 610 MHz and 325 MHz bands with the GMRT. We present the spectral ageing analysis of the source which puts an upper limit of 20 Myr on the spectral age. The better resolution maps presented here as opposed to the original 150 MHz map shows evidence for a second episode of emission. We also find that the core is detected at all four frequencies with a spectral index of 0.85, which is steeper than normal, hence we speculate that the core may be a compact steep spectrum source (CSS), which makes this giant radio galaxy a candidate triple-double radio galaxy.