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Batchelor, Saffman, and Kazantsev spectra in galactic small-scale dynamos
Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita). Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC). Carnegie Mellon University, USA; Ilia State University, Georgia.ORCID-id: 0000-0002-7304-021X
Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita). Shanghai Jiao Tong University, People’s Republic of China.ORCID-id: 0000-0002-2991-5306
Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita). Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).ORCID-id: 0000-0002-2549-6861
Rekke forfattare: 32023 (engelsk)Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 518, nr 3, s. 3312-3325Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The magnetic fields in galaxy clusters and probably also in the interstellar medium are believed to be generated by a small-scale dynamo. Theoretically, during its kinematic stage, it is characterized by a Kazantsev spectrum, which peaks at the resistive scale. It is only slightly shallower than the Saffman spectrum that is expected for random and causally connected magnetic fields. Causally disconnected fields have the even steeper Batchelor spectrum. Here, we show that all three spectra are present in the small-scale dynamo. During the kinematic stage, the Batchelor spectrum occurs on scales larger than the energy-carrying scale of the turbulence, and the Kazantsev spectrum on smaller scales within the inertial range of the turbulence – even for a magnetic Prandtl number of unity. In the saturated state, the dynamo develops a Saffman spectrum on large scales, suggestive of the build-up of long-range correlations. At large magnetic Prandtl numbers, elongated structures are seen in synthetic synchrotron emission maps showing the parity-even E polarization. We also observe a significant excess in the E polarization over the parity-odd B polarization at subresistive scales, and a deficiency at larger scales. This finding is at odds with the observed excess in the Galactic microwave foreground emission, which is believed to be associated with larger scales. The E and B polarizations may be highly non-Gaussian and skewed in the kinematic regime of the dynamo. For dust emission, however, the polarized emission is always nearly Gaussian, and the excess in the E polarization is much weaker. 

sted, utgiver, år, opplag, sider
2023. Vol. 518, nr 3, s. 3312-3325
Emneord [en]
dynamo, MHD, polarization, turbulence, galaxies: magnetic fields
HSV kategori
Identifikatorer
URN: urn:nbn:se:su:diva-215120DOI: 10.1093/mnras/stac3217ISI: 000921145500009OAI: oai:DiVA.org:su-215120DiVA, id: diva2:1741188
Tilgjengelig fra: 2023-03-03 Laget: 2023-03-03 Sist oppdatert: 2023-03-03bibliografisk kontrollert

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