A low-frequency study of recently identified double-double radio galaxies

TL;DR

This study uses low-frequency GMRT observations to confirm the episodic jet activity in 21 double-double radio galaxies, revealing their ages and identifying a new candidate quasar DDRG.

Contribution

It provides high-sensitivity low-frequency imaging of DDRGs, confirming their episodic nature and estimating their age limits, including the discovery of a new DDRG with a quasar candidate.

Findings

None of the suspected hot-spots are flat-spectrum cores.

Estimated age limits range from 11 to 52 million years.

A new DDRG with a quasar candidate was identified.

Abstract

In order to understand the possible mechanisms of recurrent jet activity in radio galaxies and quasars, which are still unclear, we have identified such sources with a large range of linear sizes (220 $-$ 917 kpc), and hence time scales of episodic activity. Here we present high-sensitivity 607-MHz Giant Metrewave Radio Telescope (GMRT) images of 21 possible double-double radio galaxies (DDRGs) identified from the FIRST survey to confirm their episodic nature. These GMRT observations show that none of the inner compact components suspected to be hot-spots of the inner doubles are cores having a flat radio spectrum, confirming the episodic nature of these radio sources. We have indentified a new DDRG with a candidate quasar, and have estimated the upper spectral age limits for eight sources which showed marginal evidence of steepening at higher frequencies. The estimated age limits (11 $-$ 52 Myr) are smaller than those of the large-sized ($\sim$ 1 Mpc) DDRGs.