Radio and X-ray Observations of the Restarted Radio Galaxy in the Galaxy Cluster CL 0838+1948

Simona Giacintucci,Wendy Peters,Tracy Clarke,Emil Polisensky,Namir E Kassim

doi:10.3390/galaxies9040108

Abstract

We present VLA Low-band Ionosphere and Transient Experiment (VLITE) 338 MHz observations of the galaxy cluster CL 0838+1948. We combine the VLITE data with Giant Metrewave Radio Telescope 610 MHz observations and survey data. The central galaxy hosts a 250 kpc source whose emission is dominated by two large lobes at low frequencies. At higher frequencies, a pair of smaller lobes (∼30 kpc) is detected within the galaxy optical envelope. The observed morphology is consistent with a restarted radio galaxy. The outer lobes have a spectral index αout=1.6, indicating that they are old, whereas the inner lobes have αinn=0.6, typical for an active source. Spectral modeling confirms that the outer emission is a dying source whose nuclear activity switched off not more than 110 Myr ago. Using archival Chandra X-ray data, we compare the radio and hot gas emission. We find that the active radio source is contained within the innermost and X-ray brightest region, possibly a galactic corona. Alternatively, it could be the remnant of a larger cool core whose outer layers have been heated by the former epoch of activity that has generated the outer lobes.

Highlights

IntroductionEvidence for recurrent radio outbursts is supported by the co-existence of a small-scale radio source with a spectral index typical for an active radio galaxy (α∼0.6–0.81 , e.g., [3]) and larger-scale, extended emission with a significantly steeper spectrum (α∼1.5–2), which is instead typical for dying or relic radio galaxies (e.g., [4,5,6])
Striking examples are the so-called double-double radio galaxies, in which two distinct pairs of radio lobes are seen on different scales: a pair of inner lobes, that are currently sustained by the active galactic nucleus (AGN) jets, and a pair of outer lobes that have been inflated during a former episode of activity [2]
We presented Very Large Array (VLA) Low-band Ionosphere and Transient Experiment (VLITE) observations at 338 MHz of the central radio galaxy in the cluster

Summary

Introduction

Evidence for recurrent radio outbursts is supported by the co-existence of a small-scale radio source with a spectral index typical for an active radio galaxy (α∼0.6–0.81 , e.g., [3]) and larger-scale, extended emission with a significantly steeper spectrum (α∼1.5–2), which is instead typical for dying or relic radio galaxies (e.g., [4,5,6]). The inner component is presently fed by the AGN, the outer remnant emission has no jets supporting the radio activity and is rapidly fading, as reflected by the pronounced steepening of its radio spectrum. An improved understanding of the statistical properties of remnant sources, and of radio galaxy evolution in general, requires larger and more representative samples of Academic Editors: Francesca Loi and Tiziana Venturi. We present a study of the restarted radio galaxy in the galaxy cluster

Results

Discussion

Conclusion