Simulation of radio plasma in clusters of galaxies

Context. M 87 is a giant elliptical galaxy located in the centre of the Virgo cluster, which harbours a supermassive black hole of mass 6.4 × 10 9 M , whose activity is responsible for the extended (80 kpc) radio lobes that surround the galaxy. The energy generated by matter falling onto the central black hole is ejected and transferred to the intra-cluster medium via a relativistic jet and morphologically complex systems of buoyant bubbles, which rise towards the edges of the extended halo. Aims. To place constraints on past activity cycles of the active nucleus, images of M 87 were produced at low radio frequencies never explored before at these high spatial resolution and dynamic range. To disentangle different synchrotron models and place constraints on source magnetic field, age and energetics, we also performed a detailed spectral analysis of M 87 extended radio-halo. Methods. We present the first observations made with the new Low-Frequency Array (LOFAR) of M 87 at frequencies down to 20 MHz. Three observations were conducted, at 15−30 MHz, 30−77 MHz and 116−162 MHz. We used these observations together with archival data to produce a low-frequency spectral index map and to perform a spectral analysis in the wide frequency range 30 MHz-10 GHz. Results. We do not find any sign of new extended emissions; on the contrary the source appears well confined by the high pressure of the intracluster medium. A continuous injection of relativistic electrons is the model that best fits our data, and provides a scenario in which the lobes are still supplied by fresh relativistic particles from the active galactic nuclei. We suggest that the discrepancy between the low-frequency radiospectral slope in the core and in the halo implies a strong adiabatic expansion of the plasma as soon as it leaves the core area. The extended halo has an equipartition magnetic field strength of 10 μG, which increases to 13 μG in the zones where the particle flows are more active. The continuous injection model for synchrotron ageing provides an age for the halo of 40 Myr, which in turn provides a jet kinetic power of 6−10 × 10 44 erg s −1 .

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“…Theoretical and numerical models to interpret these observations have also been developed by e.g. Churazov et al (2001) and Brüggen et al (2002).…”

Section: Introductionmentioning

confidence: 99%

M 87 at metre wavelengths: the LOFAR picture

Gasperin

Orrù

Murgia

et al. 2012

A&A

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“…A substantial number of bubbles have been observed in a number of clusters as depressions in the X-ray surface brightness, sometimes associated with a low level of remnant radio emission (Heinz et al, 1998;McNamara et al, 2001). Moreover, it has been shown that a lot of energy in the form of bubbles may reside in clusters as the bubbles are difficult to detect (Brüggen et al, 2002). The buoyant rise and the subsequent mixing of high-entropy gas with the cluster material can lead to a significant re-structuring of the inner regions of a cooling flow.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, we performed highly resolved two-dimensional hydrodynamic simulations of buoyant gas in a typical cluster environment similar to previous simulations of lower resolution (Brüggen et al, 2002;Quilis et al, 2001). These simulations were performed using the FLASH code (Fryxell et al, 2000), which uses an explicit piece-wise parabolic method to solve the equations of compressible hydrodynamics.…”

Section: Introductionmentioning

confidence: 99%

“…The buoyant rise and the subsequent mixing of high-entropy gas with the cluster material can lead to a significant re-structuring of the inner regions of a cooling flow. However, the details of the buoyant rise of the bubbles and the mixing with their gaseous environments are complex processes that are difficult to treat on the basis of analytical estimates alone.Therefore, we performed highly resolved two-dimensional hydrodynamic simulations of buoyant gas in a typical cluster environment similar to previous simulations of lower resolution (Brüggen et al, 2002;Quilis et al, 2001). These simulations were performed using the FLASH code (Fryxell et al, 2000), which uses an explicit piece-wise parabolic method to solve the equations of compressible hydrodynamics.…”

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confidence: 99%

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Hot bubbles from active galactic nuclei as a heat source in cooling-flow clusters

Brüggen

Kaiser

2002

Nature

238

233

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The hot plasma permeating clusters of galaxies often shows a central peak in the X-ray surface brightness that is coincident with a drop in entropy. This is taken as evidence for a cooling flow where the radiative cooling in the central regions of a cluster causes a slow subsonic inflow (e.g. Fabian, 1994). Searches in all wavebands have revealed significantly less cool gas than predicted (Böhringer et al., 2002) indicating that the mass deposition rate of cooling flows is much lower than expected. However, most cooling flow clusters host an Active Galactic Nucleus (AGN) at their centres (Burns, 1990). AGN can inflate large bubbles of hot plasma that subsequently rise through the cluster atmosphere, thus stirring this gas (Churazov et al., 2000(Churazov et al., , 2001). Here we report on the results from highly resolved hydrodynamic simulations which for the first time show that buoyant bubbles increase the cooling time in the inner cluster regions and thereby significantly reduce the deposition of cold gas. This work demonstrates that the action of AGN in the centres of cooling flow clusters can explain the observed absence of large quantities of cooled gas.The explanation of the absence of cold gas in the gaseous atmospheres of cooling flow clusters strongly suggests the presence of an, at least periodically active, source of heat in their centres. Heating the gas at the cluster centre increases its entropy and thus its radiative cooling time. However, not all heating processes will explain the observations. Fully convective heating of the cluster gas would lead to the entropy being highest in the cluster centre, opposite to what is observed (Böhringer et al., 2002).It has been suggested that the removal of cold gas and the feedback of energy through star formation and related supernovae can explain some of the observed properties of clusters (e.g. Voit & Bryan, 2001). While this is a promising scenario for the initial formation of clusters within the framework of hierarchical structure formation in the universe, the level of star formation found in detailed investigations of present-day cooling flow clusters is insufficient to explain the mass deposition rates inferred from X-ray observations (Böhringer et al., 2002). Moreover, the amount of star formation during the evolution of clusters necessary to explain the distribution of gas observed in them today, is difficult to reconcile with the observed abundances of heavy elements (Wu et al., 2000).Radio-loud AGN drive strong outflows in the form of jets that inflate bubbles or lobes. The lobes are filled with hot plasma and can heat the cluster gas in various ways. In the case of very energetic jets the expansion of the lobes will be supersonic. The resulting strong shock will heat and compress the gas (Heinz et al., 1998;Kaiser & Alexander, 1999;Reynolds et al., 2001). However, there is mounting evidence that weaker jets, which are presumably much more common, do not lead to efficient shock heating . Nevertheless, they still produce pockets of low-dens...

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“…5 Malyshkin (2001); Narayan & Medvedev (2001); Voigt et al (2002); Ruszkowski & Begelman (2002); Cho et al (2003); Soker et al (2004); Voigt & Fabian (2004); Soker (2004); Jubelgas et al (2004); Chandran & Maron (2004); Dolag et al (2004) 6 Churazov et al (2001); ; Quilis et al (2001); Brüggen et al (2002); Chandran (2004); Hoeft & Brüggen (2004); Dennis & Chandran (2005). There have been also observations of hot gas bubbles (Mazzotta et al 2004), which may also contribute to the cool core heating in a very similar way as the radio bubbles (Soker & Pizzolato 2005) …”

Section: Magnetic £Elds In Cool Coresmentioning

confidence: 97%

Magnetic turbulence in cool cores of galaxy clusters

Vogt¹,

Enßlin²

2006

Astron Nachr

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Abstract. We argue that the recently reported Kolmogorov-like magnetic turbulence spectrum in the cool core of the Hydra A galaxy cluster can be understood by kinetic energy injection by active galaxies that drives a turbulent non-helical magnetic dynamo into its saturated state. Although dramatic differences exist between small-scale dynamo scenarios, their saturated state is expected to be similar, as we show for three scenarios: the ¤ux rope dynamo, the ¤uctuation dynamo, and the explosive dynamo. Based on those scenarios, we develop an analytical model of the hydrodynamic and magnetic turbulence in cool cores. The model implies magnetic £eld strengths that £t well with Faraday rotation measurements and minimum energy estimates for the sample of cool core clusters having such data available. Predictions for magnetic £elds in clusters for which the appropriate observational information is still missing, and for yet unobserved quantities like the hydrodynamical turbulence velocity and characteristic length-scale are provided. The underlying dynamo models suggest magnetic intermittency and possibly a largescale hydrodynamic viscosity. We conclude that the success of the model to explain the £eld strength in cool core clusters indicates that in general cluster magnetic £elds directly re¤ect hydrodynamical turbulence, also in clusters without cool cores.

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Simulation of radio plasma in clusters of galaxies

Cited by 93 publications

References 46 publications

M 87 at metre wavelengths: the LOFAR picture

M 87 at metre wavelengths: the LOFAR picture

Hot bubbles from active galactic nuclei as a heat source in cooling-flow clusters

Magnetic turbulence in cool cores of galaxy clusters

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