Studium von Radio-Relikten um Galaxienhaufhen in Kosmologischen Simulationen und Vergleich mit Beobachtungen
Zusammenfassung der Projektergebnisse
The present project focused on the study of diffuse radio emission from galaxy clusters using simulations and observations. Two main signatures of large-scale radio emission can be discriminated: polarized radiation associated to elongated radio structures, generally located in the cluster outskirts, and unpolarized radiation coming from, roughly, the whole cluster volume. These radio structures are known as radio relics and radio haloes, respectively, and their origin is still a matter of debate; although there is ample evidence indicating that the non-thermal emission is produced as a result of galaxy cluster interactions strongly disturbing the intra-cluster medium (ICM). A tiny fraction of the (huge) amount of energy released during these events is believed to be channeled into the (re)acceleration of primary and secondary cosmic-ray (CR) electrons, which in the presence of magnetic fields in the ICM, give rise to the observed non-thermal radio component. In particular, radio relic structures are believed to trace the bow shocks produced in colliding galaxy clusters. The main focus of the project was the generation of a large sample -consisting of several hundreds of mock radio relics- extracted from a set of simulated galaxy clusters in a cosmological context. To do so, we used one of the largest cosmological N-body simulations available to select galaxy clusters aiming at producing new simulation runs including gas hydrodynamics at improved resolution. Then, we produced a set of mock radio relics adopting a radio emission model based on the diffusive shock acceleration scenario and a survey configuration similar to that of the NRAO VLA Sky Survey (NVSS). The latter is a low-resolution, but homogeneous, survey comprising almost the entire radio sky. This is specially suited for our purpose as it includes most of known relics, for which we have remeasured their radio and morphological properties and perform and unbiased comparison with simulations. In general, we found that the mock sample reproduces very well-known correlations for radio relics, in particular those relating the radio luminosity with the largest linear size and the X-ray luminosity. These results suggest that the morphology and abundance of merger shocks in a cosmological framework is, indeed, fully consistent with those of observed radio relics. These findings may rule out the scenario where all merger shocks are only partly illuminated by pre-existing radio plasma. If such a plasma was necessary to explain radio relics, it would have to be distributed rather homogeneously in all galaxy clusters. Our approach to the problem of diffuse emission is not only theoretical but also observational. As part of a team of observers associated to this project, we looked for diffuse radio emission in a sample of high-redshift galaxy clusters using the Giant Metrewave Radio Telescope. As a result of these observations two new radio haloes were discovered: one, in the galaxy cluster PLCK G147.3-16.6, turned out to be an archetypal large radio-emitting region most likely produced by the (re)acceleration of CR particles within the highly turbulent ICM, whereas the other, in the Phoenix galaxy cluster, turned out to be a smaller radio halo, also known as a mini-halo. The origin of such an object is possibly induced by gas sloshing generated from a minor merger event. These type of observations are needed to increase the sample of known objects to shed light on the nature of non-thermal diffuse radio emission from galaxy clusters.
Projektbezogene Publikationen (Auswahl)
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“A Distant Radio Mini-halo in the Phoenix Galaxy Cluster”, 2014, Astrophysical Journal Letters, 786, L17
van Weeren R. J.; Intema H. T., Lal D. V., Andrade-Santos F., Brüggen M., de Gasperin F., Forman W. R., Hoeft M., Jones C., Nuza S. E., Röttgering H. J. A. & Stroe A.
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“The cosmic web of the Local Universe: cosmic variance, matter content and its relation to galaxy morphology”, 2014, Monthly Notices of the Royal Astronomical Society, 445, 988
Nuza S. E., Kitaura, Francisco-Shu, Heß S., Libeskind N. I., Müller V.
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“The Discovery of a Radio Halo in PLCK G147.3-16.6 at z = 0.65”, 2014, Astrophysical Journal Letters, 781, L32
van Weeren R. J., Intema H. T., Lal D. V., Bonafede A., Jones C., Forman W. R., Röttgering H. J. A., Brüggen M., Stroe A., Hoeft M., Nuza S. E., de Gasperin F.
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“The distribution of gas in the Local Group from constrained cosmological simulations: the case for Andromeda and the Milky Way galaxies”, 2014, Monthly Notices of the Royal Astronomical Society, 441, 2593
Nuza S. E., Parisi F., Scannapieco C., Richter P., Gottlöber S., Steinmetz M.
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“Reconciling radio relic observations and simulations: The NVSS sample”, Proceedings of “The many facets of extragalactic radio surveys: towards new scientific challenges” (EXTRA-RADSUR2015), 20-23 October 2015, Bologna, Italy
Gelszinnis J., Hoeft M., Nuza S. E.
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“The Effect of Environment On Milky Way-Mass Galaxies in a Constrained Simulation of the Local Group”, 2015, Astrophysical Journal Letters, 800, L4
Creasey P., Scannapieco C., Nuza S. E., Yepes G., Gottlöber S., Steinmetz M.
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“The Milky Way and Andromeda galaxies in a constrained hydrodynamical simulation: morphological evolution”, 2015, Astronomy & Astrophysics, 577, 3
Scannapieco C., Creasey P., Nuza S. E., Yepes G., Gottlöber S., Steinmetz M.
