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Batchelor, Saffman, and Kazantsev spectra in galactic small-scale dynamos
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Oskar Klein Ctr, Dept Astron, AlbaNova, SE-10691 Stockholm, Sweden.;Carnegie Mellon Univ, Dept Phys, 5000 Forbes Ave, Pittsburgh, PA 15213 USA.;Carnegie Mellon Univ, McWilliams Ctr Cosmol, 5000 Forbes Ave, Pittsburgh, PA 15213 USA.;Ilia State Univ, Sch Nat Sci & Med, 3 5 Cholokashvili Ave, Tbilisi 0194, Georgia.;Shanghai Jiao Tong Univ, Tsung Dao Lee Inst, 800 Dongchuan Rd, Shanghai 200240, Peoples R China..ORCID iD: 0000-0002-7304-021X
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Nordita SU; Stockholm Univ, Hannes Alfvensvag 12, SE-10691 Stockholm, Sweden..
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Nordita SU; Stockholm Univ, Hannes Alfvensvag 12, SE-10691 Stockholm, Sweden..
2022 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 518, no 3, p. 3312-3325Article in journal (Refereed) 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.

Place, publisher, year, edition, pages
Oxford University Press (OUP) , 2022. Vol. 518, no 3, p. 3312-3325
Keywords [en]
dynamo, MHD, polarization, turbulence, galaxies: magnetic fields
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-324486DOI: 10.1093/mnras/stac3217ISI: 000921145500009Scopus ID: 2-s2.0-85143736197OAI: oai:DiVA.org:kth-324486DiVA, id: diva2:1741944
Note

QC 20230307

Available from: 2023-03-07 Created: 2023-03-07 Last updated: 2024-08-28Bibliographically approved

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Brandenburg, AxelZhou, HongzheSharma, Ramkishor

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