J0041+3224: a new double-double radio galaxy

Abstract

We report the discovery of a double-double radio galaxy (DDRG), J0041+3224, with the Giant Metrewave Radio Telescope (GMRT) and subsequent high-frequency observations with the Very Large Array (VLA). The inner and outer doubles are aligned within about 4 deg and are reasonably collinear with the parent optical galaxy. The outer double has a steeper radio spectrum compared with the inner one. Using an estimated redshift of 0.45, the projected linear sizes of the outer and inner doubles are 969 and 171 kpc respectively. The time scale of interruption of jet activity has been estimated to be about 20 Myr, similar to other known DDRGs. We have compiled a sample of known DDRGs, and have re-examined the inverse correlation between the ratio of the luminosities of the outer to the inner double and the size of the inner double, l_{in}. Unlike the other DDRGs with l_{in} larger than about 50 kpc, the inner double of J0041+3224 is marginally more luminous than the outer one. The two DDRGs with l_{in} less than about a few kpc have a more luminous inner double than the outer one, possibly due to a higher efficiency of conversion of beam energy as the jets propagate through the dense interstellar medium. We have examined the symmetry parameters and find that the inner doubles appear to be more asymmetric in both its armlength and flux density ratios compared with the outer doubles, although they appear marginally more collinear with the core than the outer double. We discuss briefly possible implications of these trends.Comment: Accepted for publication in MNRAS, 9 pages, 10 figure

Episodic Activity in Active Galactic Nuclei

“…As an example, the radio image of the DDRG J0041+3224 discovered using the Giant Metrewave Radio Telescope by Saikia, Konar & Kulkarni 2006 [15] is shown in Figure 1. More than about a dozen good examples of such DDRGs are known.…”

Deep low-frequency observations with the Giant Metrewave Radio Telescope: a search for relic radio emission

“…The most striking examples of such episodic nuclear activity are the ‘double–double’ radio galaxies (DDRGs) where a young pair of radio lobes is seen closer to the nucleus in addition to the older and more distant lobes of emission (e.g. Subrahmanyan, Saripalli & Hunstead 1996; Lara et al 1999; Schoenmakers et al 2000; Saikia, Konar & Kulkarni 2006, and references therein). In addition to the DDRGs, diffuse relic radio emission due to an earlier cycle of activity has also been suggested for a number of sources from structural and spectral information.…”

VLBI observation of giant radio galaxy J1313+696 at 2.3/8.4 GHz

“…Among the large radio sources, the radio galaxies whose lobes span a (projected) distance of above 1 Mpc are called giant radio galaxies (GRGs), and X. Liu ( ) · J. Liu National Astronomical Observatories/Urumqi observatory, CAS, 40-5 South Beijing Rd., Urumqi 830011, People's Republic of China e-mail: liux@uao.ac.cn J. Liu Graduate University of the Chinese Academy of Sciences, Beijing 100049, People's Republic of China the majority of them are FRII sources (Schoenmakers et al 2001). A small number of the large extended sources consisting of a pair of double lobes have been called doubledouble radio galaxies (DDRGs), and the observed structures of DDRGs suggest recurrent or interrupted central activity as the origin of these sources (Schoenmakers et al 2000a;Saikia et al 2006). The large radio sources have been observed with telescopes or arrays at relatively low resolution but not well observed with the very long baseline interferometry (VLBI).…”