Conference Note: A Taxonomy of Extended Radio Sources in Clusters of Galaxies (original) (raw)

A Taxonomy of Extended Radio Sources in Clusters of Galaxies

Arxiv preprint astro-ph/ …, 2003

At the request of the conference attendees, we have compiled a classification of ex-tended radio sources in clusters. These range from scales of tens of parsecs to over a megaparsec in scale, and include both sources associated with AGN and sources thought to derive from ...

Extended diffuse radio emission in galaxy clusters

2019

Galaxy clusters are the most massive gravitationally bound systems in the universe which grow through mergers with other clusters, galaxy groups, and accretion of gas. The mergers generate shocks and turbulence in the intra-cluster medium (ICM). Along the shock edges, particles are accelerated to relativistic energies through multiple crossings at the shock front. The extended diffuse emission sources formed as a result are commonly classified as radio halos and radio relics. The precise nature and origin of the relativistic particles is nevertheless not well understood. We study the nature of the radio relic candidate in Abell 115. We obtain it's spectral properties using radio continuum observations at 150\,MHz with LOFAR, 610\,MHz with the GMRT, and 1.5\,GHz with the VLA. We confirm it's nature as a radio relic. Polarization analyses suggest that part of the large scale synchrotron source is embedded in a region of high ICM density. We show that the galaxy cluster A1430 h...

The Evolution of Diffuse Radio Sources in Galaxy Clusters

The Astrophysical Journal, 2004

We investigate the evolution and number distribution of radio halos in galaxy clusters. Without re-acceleration or regeneration, the relativistic electrons responsible for the diffuse radio emission will lose their energy via inverse-Compton and synchrotron losses in a rather short time, and radio halos will have lifetimes ∼ 0.1 Gyr. Radio halos could last for ∼ Gyr if a significant level of re-acceleration is involved. The lifetimes of radio halos would be comparable with the cosmological time if the radio-emitting electrons are mainly the secondary electrons generated by pion decay following proton-proton collisions between cosmic-ray protons and the thermal intra-cluster medium within the galaxy clusters. Adopting both observational and theoretical constraints for the formation of radio halos, we calculate the formation rates and the comoving number density of radio halos in the hierarchical clustering scheme. Comparing with observations, we find that the lifetimes of radio halos are ∼ Gyr. Our results indicate that a significant level of re-acceleration is necessary for the observed radio halos and the secondary electrons may not be a dominant origin for radio halos.

The origin of radio haloes and non-thermal emission in clusters of galaxies

Monthly Notices of the Royal Astronomical Society, 2002

We study the origin of the non-thermal emission from the intracluster medium, including the excess hard X-ray emission and cluster-wide radio haloes, through fitting two representative models to the Coma cluster. If the synchrotron emitting relativistic electrons are accelerated in situ from the vast pool of thermal electrons, then a quasi-stationary solution of the kinetic equation with particle acceleration through turbulence at high energies (> 200 keV) naturally produces a population of supra-thermal electrons responsible for the excess hard X-ray emission through bremsstrahlung. Inverse Compton scattering is negligible at hard X-ray energies in this case. The radio halo flux density constrains the magnetic field strength to a value close to that of equipartition ∼ 1µG. Alternatively, if the relativistic electrons are injected from numerous localised 'external' sources then the hard X-rays are best explained by inverse Compton scattering from GeV electrons, and little of the hard X-radiation has a bremsstrahlung origin. In this case, the magnetic field strength is constrained to ∼ 0.1 − 0.2 µG. Both models assume that the non-thermal emissions are generated by a single electron spectrum, so that only two free parameters, well constrained by the observed hard X-ray and radio halo spectra, are needed in either case. Measurements of the cluster magnetic field will distinguish between the models.

Radio relic and the diffuse emission trail discovered in low-mass galaxy cluster Abell 1697

Astronomy & Astrophysics

We report the discovery of a putative radio relic, 830 kpc in length, and found towards the outskirts of galaxy cluster Abell 1697 (z = 0.181), using the LOFAR Two Meter Sky Survey at 144 MHz. An X-ray-inferred mass of M500X-ray = 2.9−0.7+0.8 × 1014 M⊙ places Abell 1697 among the least massive relic hosts. The relic is also detected at 325 MHz in the Westerbork Northern Sky Survey and at 1.4 GHz in the NRAO VLA Sky Survey, with an average spectral index of α(144, 325, 1400 MHz) = − 0.98 ± 0.01, and magnetic field of Beq ∼ 0.6 μG. This relic, located in the north-east periphery of the cluster, is 300 kpc wide, exhibits a gradual spectral steepening across the width ( α144 MHz1.4 GHz(inj) = −0.70 ± 0.11 to α144 MHz1.4 GHz(edge) = −1.19 ± 0.15 ), as well as indications of a co-spatial X-ray (ROSAT) shock and the radio relic emission. The radio power of the relic is P1.4 GHz = 8.5 ± 1.1 × 1023 W Hz−1, which is found to be in good agreement with the expected empirical correlation between...

Nonthermal emission from the radio relic of the galaxy cluster A2256

Astronomische Nachrichten, 2011

We aim to obtain a consistent description of non-thermal emissions from Abell 2256 and to give a prediction for a gamma-ray emission from this galaxy cluster. Assuming that a radio relic illuminates a localization of an ongoing merger, and that both radio and non-thermal part of hard X-ray emission are due to electron component of cosmic rays filling the relic, we derived from radio and hard X-ray properties of the relic in A2256 the magnetic field strength and number densities for relativistic electrons and protons. Due to the interpretation of the radio relic as a structure formed just where a shock front is, we discuss a gamma-ray emission at the cluster periphery. The estimated strength of the magnetic field in the relic is equal to 0.05 µG, while the amplitude of the electron number density varies from 3 • 10 −4 to 3 • 10 −5 cm −3 (respectively for the relic thickness of 50 to 500 kpc). We got a substantial degree of non-equipartition between cosmic rays and magnetic field in the relic region, where the CR pressure is approaching that of thermal gas. Our prediction for LOFAR is a synchrotron flux from the relic region of the order of ∼6 Jy at 60MHz and ∼10 Jy at 30MHz. The lower limit of the γ-ray flux from the relic region calculated for a hadronic channel is of the order of 10 −12 erg cm −2 .

Gamma-ray emission from galaxy cluster outskirts versus radio relics

Astronomy & Astrophysics, 2016

Context. Galaxy cluster peripheries provide important information on the nature of ICM/IGM linkage. In this paper we consider potential future observations in the gamma-ray domain at cluster edges involving the radio relic phenomenon. Aims. We focus on the spectral signature of gamma radiation that should be evident in the energy range of Fermi-LAT, i.e. 10 −1 GeV and the CTA energy range ∼10 2 GeV. The spectral signature results from a comparable gamma-ray flux due to the IC and π 0 decay on the edge of the cluster, and its spectral position is a function of the magnetic field and relative efficiency of the acceleration of protons and electrons. We aim to draw attention to the dependence of the gamma-ray structure on the magnetic field value. Methods. As an example, we carried out analyses of two types of non-thermal diffuse radio emission: the radio relic of A 2256 and the radio halo of Coma cluster. We suggest that in both cases the expected spatially correlated gamma-ray spectrum should have a characteristic structure that depends on the strength of the local magnetic field. In both of the clusters we calculated the combined flux of gamma radiation from the actual observational values of the used observables. Results. The revealed spectral dependence on the magnetic field would allow us to relate the future spectral observations, in particular the position of the gamma-ray signature, to the value of the magnetic field in the border area between galaxy clusters and their connecting filaments, possibly constraining the estimated relative efficiency of particle acceleration at the edge of the cluster.

Probing Cosmic Rays in AGN and Clusters of Galaxies using radio observations

Proceedings of ISKAF2010 Science Meeting — PoS(ISKAF2010)

We search for radio structures not associated with Active Galactic Nuclei (e.g. haloes, mini halos, relics) in a sample of 70 Abell clusters for which we have radio, optical and X-ray data. Radio galaxies are known sources of high energy. Most galaxy clusters have cool cores with active galaxies at their centre. These AGN contain particle bubbles that show nonthermal radio emission. We are probing the role that intracluster magnetic fields, mergers, cooling flows, radio jets/shocks as well as radio halos/relics play in the formation and acceleration of cosmic rays. Faraday rotation quantitatively establishes both cosmic ray and magnetic pressure component in the intracluster medium. Rotation measurements of background and cluster radio sources, together with X-ray observations provide the main evidence of large-scale intra-cluster magnetic fields and of densities of relativistic electrons. The intracluster medium of galaxy clusters is permeated by significant magnetic fields, which suggests that trapping and acceleration of cosmic rays by the external magnetic field could be occuring. Radio spectral observations indicate the ageing of the emitting particles. In the current paper we discuss results from the radio and X-ray analysis of two powerful radio galaxies from our sample namely Hercules A, and 3C 388.

Radio AGN in Fossil Groups of Galaxies

2016

We present the first systematic 1.4 GHz Very Large Array radio continuum survey of fossil galaxy group candidates. These are virialized systems believed to have assembled over a gigayear in the past through the merging of galaxy group members into a single, isolated, massive elliptical galaxy and featuring an extended hot X-ray halo. We use new photometric and spectroscopic data from SDSS Data Release 7 to determine that three of the candidates are clearly not fossil groups. Of the remaining 30 candidates, 67% contain a radio-loud (L 1.4GHz > 10 23 W Hz −1) active galactic nucleus (AGN) at the center of their dominant elliptical galaxy. We find a weak correlation between the radio luminosity of the AGN and the X-ray luminosity of the halo suggesting that the AGN contributes to energy deposition into the intragroup medium. We only find a correlation between the radio and optical luminosity of the central elliptical galaxy when we include X-ray selected, elliptically dominated non-fossil groups, indicating a weak relationship between AGN strength and the mass assembly history of the groups. The dominant elliptical galaxy of fossil groups is on average roughly an order of magnitude more luminous than normal group elliptical galaxies in optical, X-ray, and radio luminosities and our findings are consistent with previous results that the radio-loud fraction in elliptical galaxies is linked to the stellar mass of a population. The current level of activity in fossil groups suggests that AGN fueling continues long after the last major merger. We discuss several possibilities for fueling the AGN at the present epoch.

Focus Meeting #3: Radio Galaxies – Resolving the AGN Phenomenon

Proceedings of the International Astronomical Union, 2018

Radio galaxies provide excellent laboratories for investigating the physical aspects, unification and cosmic evolution of active galactic nuclei (AGN). Thanks to recent multiwavelength observations, we are now able to separate many different physical components of radio galaxies through imaging and spectroscopy. Observations from radio through X-ray wavelengths can probe the ejection of matter into jets and monitor decades of jet evolution. Gamma-ray observations have shown that radio galaxies are detectable up to the very-high-energy range despite unfavorable jet alignment. We observe radio galaxies out to redshifts greater than z = 5, which makes them important cosmological probes. Planck maps have provided us with new insights into the populations of radio galaxies and their distributions in space in the 30 − 900 GHz range. NuSTAR provides high-quality spectra in the hard X-ray range. The Event Horizon Telescope (EHT) has begun mapping close to the event horizon of the Milky Way's central black hole, and the Square Kilometre Array (SKA), the next generation of extremely large telescopes (ELTs) and other future telescopes will open up a new and vast discovery space. Focus Meeting #3 brought together multiwavelength observers and theorists to synthesize progress made over the last three years and to define future directions. In order to channel the presentations and discussions, the meeting was organized into five sessions: • During the first session, starting on August 22nd, we discussed the radio-galaxy structures that are produced on kiloparsec scales and beyond, with an emphasis on plasma composition, and sought to address their underlying causes. Daniel Schwartz (Harvard-Smithsonian Center for Astrophysics, USA) talked about high-resolution studies of 100 kpc jets based on data from the Chandra X-ray Observatory. For example, a new Chandra survey for jets in radio quasars at z > 3 has revealed X-ray jets and lobes extending beyond the region of detected radio emission (Schwartz 2018). • The second session focused on the central engine and production of the jet(s). Alexander Tchekhovskoy (University of California, Berkeley, USA) introduced the topic with a presentation about how numerical simulations incorporating general relativity and magnetism allow us to use black hole accretion phenomena to quantitatively probe strong-field gravity and constrain black hole physics in various astrophysical contexts. • On the second day of the meeting we first discussed populations and statistics of radio galaxies, motivated by a review from Elaine Sadler (University of Sydney, Australia) focusing on results from multi-wavelength radio surveys. • This was followed by a session about future prospects. Lindy Blackburn (Harvard-Smithsonian Center for Astrophysics, USA) started the discussion with a presentation on the goals and status of the EHT, which has already revealed structure on the scale of † This article was originally published with its supplementary material missing. This has since been updated in the online PDF and HTML versions and a correction notice has been published.