Cosmic ray transport in galaxy clusters: implications for radio halos, gamma-ray signatures, and cool core heating

Enßlin, T. A.; Pfrommer, Christoph; Miniati, Francesco; Subramanian, Kandaswamy

doi:10.1051/0004-6361/201015652

Cited by 197 publications

(296 citation statements)

References 168 publications

Supporting

Mentioning

290

Contrasting

Order By: Relevance

“…Conversely, to date no haloes have been detected in dynamically relaxed clusters . These results support the importance of turbulence in re-accelerating and confining the emitting particles in cluster mergers Enßlin et al 2011).…”

Section: Introductionsupporting

confidence: 80%

Low frequency follow up of radio haloes and relics in the GMRT Radio Halo Cluster Survey

Venturi

Giacintucci

Dallacasa

et al. 2013

A&A

View full text Add to dashboard Cite

Aims. To gain insight into the origin of diffuse radio sources in galaxy clusters and their connection with cluster merger processes, we performed GMRT low frequency observations of the radio haloes, relics and new candidates belonging to the GMRT radio Halo cluster sample first observed at 610 MHz. Our main aim was to investigate their observational properties and integrated spectra at frequencies below 610 MHz. Methods. High sensitivity imaging was performed using the GMRT at 325 MHz and 240 MHz. The properties of the diffuse emission in each cluster were compared to our 610 MHz images and/or literature information available at other frequencies, in order to derive the integrated spectra over a wide frequency range. Results. Cluster radio haloes form a composite class in terms of spectral properties. Beyond the classical radio haloes, whose spectral index α is in the range ∼1.2 ÷ 1.3 (S ∝ ν −α ), we found sources with α ∼ 1.6 ÷ 1.9. This result supports the idea that the spectra of the radiating particles in radio haloes is not universal and that inefficient mechanisms of particle acceleration are responsible for their origin. We also found a variety of brightness distributions, i.e. both centrally peaked and clumpy haloes. Even though the thermal and relativistic plasma tend to occupy the same cluster volume, in some cases a positional shift between the radio and X-ray peaks of emission is evident. Our observations also revealed diffuse cluster sources that cannot be easily classified as either haloes or relics. New candidate relics were found in A 1300 and in A 1682, and in some clusters "bridges" of radio emission have been detected, connecting the relic and radio halo emission. Finally, by combining our new data with information in the literature, we derived the Log L X -Log P 325 MHz correlation for radio haloes, and investigated the possible correlation of the spectral index of radio haloes with the temperature of the intracluster medium.

show abstract

Section: Introductionsupporting

confidence: 80%

Low frequency follow up of radio haloes and relics in the GMRT Radio Halo Cluster Survey

Venturi

Giacintucci

Dallacasa

et al. 2013

A&A

View full text Add to dashboard Cite

show abstract

“…However, as streaming needs longer stretches of the ordered field to be effective, it may not be important in the turbulent thin disk of galaxies (Dogiel & Breitschwerdt 2012;Enßlin et al 2011). Furthermore, there is evidence that in the Milky Way on scales <1 kpc CRE propagation is isotropic (Strong et al 2007;Stepanov et al 2012), which is inconsistent with streaming.…”

Section: Cre Propagation Modelsmentioning

confidence: 99%

Multi-scale radio-infrared correlations in M 31 and M 33: The role of magnetic fields and star formation

Tabatabaei

Berkhuijsen

Frick

et al. 2013

A&A

101

View full text Add to dashboard Cite

Interstellar magnetic fields and the propagation of cosmic ray electrons have an important impact on the radio-infrared (IR) correlation in galaxies. This becomes evident when studying different spatial scales within galaxies. We investigate the correlation between the IR and free-free/synchrotron radio continuum emission at 20 cm from the two local group galaxies M 31 and M 33 on spatial scales between 0.4 and 10 kpc. The multi-scale radio-IR correlations have been carried out using a wavelet analysis. The free-free and IR emission are correlated on all scales, but on some scales the synchrotron emission is only marginally correlated with the IR emission. The synchrotron-IR correlation is stronger in M 33 than in M 31 on small scales (<1 kpc), but it is weaker than in M 31 on larger scales. Taking the smallest scale on which the synchrotron-IR correlation exists as the propagation length of cosmic ray electrons, we show that the difference on small scales can be explained by the smaller propagation length in M 33 than in M 31. On large scales, the difference is due to the thick disk/halo in M 33, which is absent in M 31. A comparison of our data with data on NGC 6946, the LMC and M 51 suggests that the propagation length is determined by the ratio of ordered-to-turbulent magnetic field strength, which is consistent with diffusion of CR electrons in the ISM. As the diffusion length of CR electrons influences the radio-IR correlation, this dependence is a direct observational evidence of the importance of magnetic fields for the radio-IR correlation within galaxies. The star-formation rate per surface area only indirectly influences the diffusion length as it increases the strength of the turbulent magnetic field.

show abstract

“…Potentially several mechanisms may be responsible for the generation of Mpc scale synchrotron emission from galaxy clusters. Relativistic electrons in the ICM can be re-accelerated in situ through interaction with turbulence generated in the ICM by cluster-cluster mergers (Brunetti et al 2001;Petrosian 2001), or secondary electrons can be continuously injected in the ICM by inelastic collisions between relativistic and thermal protons (Dennison 1980;Blasi & Colafrancesco 1999;Dolag & Enßlin 2000;Enßlin et al 2011). Models considering a combination of the two mechanisms, namely the re-acceleration of both relativistic protons and their secondaries by magnetohydrodynamical turbulence generated in the ICM have been recently considered (Brunetti & Blasi 2005;Dolag et al 2008;Brunetti & Lazarian 2011).…”

Section: Introductionmentioning

confidence: 99%

First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256

Weeren¹,

Röttgering²,

Rafferty³

et al. 2012

A&A

View full text Add to dashboard Cite

Abell 2256 is one of the best known examples of a galaxy cluster hosting large-scale diffuse radio emission that is unrelated to individual galaxies. It contains both a giant radio halo and a relic, as well as a number of head-tail sources and smaller diffuse steep-spectrum radio sources. The origin of radio halos and relics is still being debated, but over the last years it has become clear that the presence of these radio sources is closely related to galaxy cluster merger events. Here we present the results from the first LOFAR low band antenna (LBA) observations of Abell 2256 between 18 and 67 MHz. To our knowledge, the image presented in this paper at 63 MHz is the deepest ever obtained at frequencies below 100 MHz in general. Both the radio halo and the giant relic are detected in the image at 63 MHz, and the diffuse radio emission remains visible at frequencies as low as 20 MHz. The observations confirm the presence of a previously claimed ultra-steep spectrum source to the west of the cluster center with a spectral index of −2.3 ± 0.4 between 63 and 153 MHz. The steep spectrum suggests that this source is an old part of a head-tail radio source in the cluster. For the radio relic we find an integrated spectral index of −0.81 ± 0.03, after removing the flux contribution from the other sources. This is relatively flat which could indicate that the efficiency of particle acceleration at the shock substantially changed in the last ∼0.1 Gyr due to an increase of the shock Mach number. In an alternative scenario, particles are re-accelerated by some mechanism in the downstream region of the shock, resulting in the relatively flat integrated radio spectrum. In the radio halo region we find indications of low-frequency spectral steepening which may suggest that relativistic particles are accelerated in a rather inhomogeneous turbulent region.

show abstract

Cosmic ray transport in galaxy clusters: implications for radio halos, gamma-ray signatures, and cool core heating

Cited by 197 publications

References 168 publications

Low frequency follow up of radio haloes and relics in the GMRT Radio Halo Cluster Survey

Low frequency follow up of radio haloes and relics in the GMRT Radio Halo Cluster Survey

Multi-scale radio-infrared correlations in M 31 and M 33: The role of magnetic fields and star formation

First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256

Contact Info

Product

Resources

About