Four Extreme Relic Radio Sources in Clusters of Galaxies

By O. Slee, Alan L. Roy, M. Murgia, Heinz Andernach, M. Ehle. 2001

167 citations recorded by the source corpus.

We describe the results of the highest-resolution radio observations yet made of four relic radio sources in the Abell clusters A13, A85, A133, and A4038. Our Very Large Array images at 1.4 GHz with 4″ resolution and a noise level of 1 σ ∼ 20 μJy beam-1 (1.1 K) show a remarkable variety of fine structure in the form of spectacular arcs, wisps, plumes, and loops. Their integrated radio flux densities fall very rapidly with frequency, with power-law slopes, α, between 2.1 and 4.4 near 1.4 GHz [where Sν ∝ (ν/ν 0)-α]. The relics possess linear polarization levels ranging between 2.3% (A133) and 35% (A85); the higher polarization fractions imply a highly ordered magnetic field in the fine structure and low differential Faraday rotation in the intervening cluster gas. The optical identification of a host galaxy formerly associated with a relic remains problematic. In A85, A133, and A4038 the travel times for the brightest cluster galaxies are significantly longer than the modeled ages of the relics; there is always at least one nearby relatively bright elliptical galaxy that provides a better match. Excess X-ray emission in the 0.5 to 2 keV band was found near the relics in A85 and A133. The surface brightness was too high to be attributed to the inverse Compton mechanism alone. We found excellent fits to the broadband radio spectra using the anisotropic model of spectral aging, and we have extended the model to include diffusion of particles between regions of different field strength. The steep radio spectra imply ages for the relics of ∼108 yr, at the start of which period their radio luminosities would have been ∼1025 W Hz-1 at 1.4 GHz, and so their progenitors were on the boundary between FR I and FR II radio galaxies and hence among the most luminous 7% of radio galaxies. We find that the relics are in approximate pressure equilibrium with the surrounding intracluster gas, which has probably limited their free expansion and prevented them from fading by adiabatic cooling.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/1380bbf575daba482b09a209da43d4301d0e7686

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Citations in the corpus

On the formation of cluster radio relics (2001, background): “Such filaments and tori appear to be observed by very recent high-resolution radio maps of cluster radio relics (Slee et al. 2001).”
What is a cool-core cluster? a detailed analysis of the cores of the X-ray flux-limited HIFLUGCS cluster sample (2009, background): “This SCC cluster hosts a radio relic, that is close to but not connected to the central radio galaxy (e.g Slee et al. 2001b).”
Radio signature of cosmological structure formation shocks (2006, background): “The radio relic in A85 (Slee et al. 2001) may serve due to its size, morphology, and strong polarization as prototype for the radio phoenix class.”
The VLA Low-Frequency Sky Survey (2005, background): “These include halos and relics in clusters of galaxies (Ensslin & Röttgering 2002), fossil radio galaxies (Slee et al. 2001), high-redshift radio galaxies (Chambers et al. 1987; De Breuck et al. 2000), and pulsars.”
Cosmic-Ray Electrons in Groups and Clusters of Galaxies: Primary and Secondary Populations from a Numerical Cosmological Simulation (2001, background): “However, recent radio observations have shown that a sample of radio relics with sizes up to a few hundred kpc observed at very high resolution in a number of galaxy clusters possess just these morphological features (Slee et al. 2001).”
Diffuse Radio Emission from Galaxy Clusters (2019, background): “…and filamentary (e.g., Abell 13, Abell 85, Abell 2048, Abell 4038, Abell 2443, Abell 103319, Abell 1914, Abell 1931, and the Ophiuchus cluster, Slee et al. 1983, 2001; van Weeren et al. 2011d; de Gasperin et al. 2015b; van Weeren et al. 2009a; Werner et al. 2016; Murgia et al. 2010a; Brüggen…”
Cosmic ray transport in galaxy clusters: implications for radio halos, gamma-ray signatures, and cool core heating (2010, background): “10 Radio phoenix in the taxonomy of Kempner et al. (2004): Enßlin & Gopal-Krishna (2001); Slee et al. (2001); Enßlin et al. (2001); Enßlin & Brüggen (2002); Kaiser & Cotter (2002); Brüggen et al. (2003); Gardini & Ricker (2004).”