Schleicher, Dominik R. G.

[["dc.bibliographiccitation.artnumber","A87"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","560"],["dc.contributor.author","Schober, Jennifer"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Klessen, Ralf S."],["dc.date.accessioned","2018-11-07T09:16:53Z"],["dc.date.available","2018-11-07T09:16:53Z"],["dc.date.issued","2013"],["dc.description.abstract","The Universe at present is highly magnetized, with fields of a few 10 5 G and coherence lengths greater than 10 kpc in typical galaxies like the Milky Way. We propose that the magnetic field was already amplified to these values during the formation and the early evolution of galaxies. Turbulence in young galaxies is driven by accretion, as well as by supernova (SN) explosions of the first generation of stars. The small-scale dynamo can convert the turbulent kinetic energy into magnetic energy and amplify very weak primordial seed fields on short timescales. Amplification takes place in two phases: in the kinematic phase the magnetic field grows exponentially, with the largest growth rate on the smallest nonresistive scale. In the following nonlinear phase the magnetic energy is shifted toward larger scales until the dynamo saturates on the turbulent forcing scale. To describe the amplification of the magnetic field quantitatively, we modeled the microphysics in the interstellar medium (ISM) of young galaxies and determined the growth rate of the small-scale dynamo. We estimated the resulting saturation field strengths and dynamo timescales for two turbulent forcing mechanisms: accretion-driven turbulence and SN-driven turbulence. We compare them to the field strength that is reached when only stellar magnetic fields are distributed by SN explosions. We find that the small-scale dynamo is much more efficient in magnetizing the ISM of young galaxies. In the case of accretion-driven turbulence, a magnetic field strength on the order of 10 6 G is reached after a time of 24 270 Myr, while in SN-driven turbulence the dynamo saturates at field strengths of typically 10 5 G after only 4 15 Myr. This is considerably shorter than the Hubble time. Our work can help for understanding why present-day galaxies are highly magnetized."],["dc.identifier.doi","10.1051/0004-6361/201322185"],["dc.identifier.isi","000328754500087"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10883"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/28038"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Magnetic field amplification in young galaxies"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","013055"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","New Journal of Physics"],["dc.bibliographiccitation.volume","15"],["dc.contributor.affiliation","Bovino, S;"],["dc.contributor.affiliation","Schleicher, D R G;"],["dc.contributor.affiliation","Schober, J;"],["dc.contributor.author","Bovino, Stefano"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Schober, Jennifer"],["dc.date.accessioned","2018-11-07T09:29:02Z"],["dc.date.available","2018-11-07T09:29:02Z"],["dc.date.issued","2013"],["dc.date.updated","2022-02-10T06:47:23Z"],["dc.description.abstract","The small-scale dynamo provides a highly efficient mechanism for the conversion of turbulent into magnetic energy. In astrophysical environments, such turbulence often occurs at high Mach numbers, implying steep slopes in the turbulent spectra. It is thus a central question whether the small-scale dynamo can amplify magnetic fields in the interstellar or intergalactic media, where such Mach numbers occur. To address this long-standing issue, we employ the Kazantsev model for turbulent magnetic field amplification, systematically exploring the effect of different turbulent slopes, as expected for Kolmogorov, Burgers, the Larson laws and results derived from numerical simulations. With the framework employed here, we give the first solution encompassing the complete range of magnetic Prandtl numbers, including Pm << 1, Pm similar to 1 and Pm >> 1. We derive scaling laws of the growth rate as a function of hydrodynamic and magnetic Reynolds number for Pm similar to 1 and Pm >> 1 for all types of turbulence. A central result concerns the regime of Pm similar to 1, where the magnetic field amplification rate increases rapidly as a function of Pm. This phenomenon occurs for all types of turbulence we have explored. We further find that the dynamo growth rate can be decreased by a few orders of magnitude for turbulence spectra steeper than Kolmogorov. We calculate the critical magnetic Reynolds number Rm(c) for magnetic field amplification, which is highest for the Burgers case. As expected, our calculation shows a linear behaviour of the amplification rate close to the threshold proportional to (Rm - Rm(c)). On the basis of the Kazantsev model, we therefore expect the existence of the small-scale dynamo for a given value of Pm as long as the magnetic Reynolds number is above the critical threshold."],["dc.description.sponsorship","Open-Access-Publikationsfonds 2013"],["dc.identifier.doi","10.1088/1367-2630/15/1/013055"],["dc.identifier.eissn","1367-2630"],["dc.identifier.fs","602614"],["dc.identifier.isi","000314341600002"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/8703"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/30926"],["dc.language.iso","en"],["dc.notes","PACS: 98.62.En Electric and magnetic fields\r\n\r\n95.30.Lz Hydrodynamics\r\n\r\n98.58.Ay Physical properties (abundances, electron density, magnetic fields, scintillation, scattering, kinematics, dynamics, turbulence, etc.)"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","IOP Publishing"],["dc.relation.issn","1367-2630"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights.uri","http://creativecommons.org/licenses/by/3.0/"],["dc.title","Turbulent magnetic field amplification from the smallest to the largest magnetic Prandtl numbers"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","023017"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","New Journal of Physics"],["dc.bibliographiccitation.volume","15"],["dc.contributor.affiliation","Schleicher, Dominik R G;"],["dc.contributor.affiliation","Schober, Jennifer;"],["dc.contributor.affiliation","Federrath, Christoph;"],["dc.contributor.affiliation","Bovino, Stefano;"],["dc.contributor.affiliation","Schmidt, Wolfram;"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Schober, Jennifer"],["dc.contributor.author","Federrath, Christoph"],["dc.contributor.author","Bovino, Stefano"],["dc.contributor.author","Schmidt, Wolfram"],["dc.date.accessioned","2018-11-07T09:28:14Z"],["dc.date.available","2018-11-07T09:28:14Z"],["dc.date.issued","2013"],["dc.date.updated","2022-02-10T08:30:38Z"],["dc.description.abstract","The small-scale dynamo plays a substantial role in magnetizing the Universe under a large range of conditions, including subsonic turbulence at low Mach numbers, highly supersonic turbulence at high Mach numbers and a large range of magnetic Prandtl numbers Pm, i.e. the ratio of kinetic viscosity to magnetic resistivity. Low Mach numbers may, in particular, lead to the well-known, incompressible Kolmogorov turbulence, while for high Mach numbers, we are in the highly compressible regime, thus close to Burgers turbulence. In this paper, we explore whether in this large range of conditions, universal behavior can be expected. Our starting point is previous investigations in the kinematic regime. Here, analytic studies based on the Kazantsev model have shown that the behavior of the dynamo depends significantly on Pm and the type of turbulence, and numerical simulations indicate a strong dependence of the growth rate on the Mach number of the flow. Once the magnetic field saturates on the current amplification scale, backreactions occur and the growth is shifted to the next-larger scale. We employ a Fokker-Planck model to calculate the magnetic field amplification during the nonlinear regime, and find a resulting power-law growth that depends on the type of turbulence invoked. For Kolmogorov turbulence, we confirm previous results suggesting a linear growth of magnetic energy. For more general turbulent spectra, where the turbulent velocity scales with the characteristic length scale as u(e)alpha e(v) we find that the magnetic energy grows as (t/T-ed)(2v/( 1-v)), with t being the time coordinate and T-ed the eddy-turnover time on the forcing scale of turbulence. For Burgers turbulence, v = 1/2, quadratic rather than linear growth may thus be expected, as the spectral energy increases from smaller to larger scales more rapidly. The quadratic growth is due to the initially smaller growth rates obtained for Burgers turbulence. Similarly, we show that the characteristic length scale of the magnetic field grows as t(1/(1-v)) in the general case, implying t(3/2) for Kolmogorov and t(2) for Burgers turbulence. Overall, we find that high Mach numbers, as typically associated with steep spectra of turbulence, may break the previously postulated universality, and introduce a dependence on the environment also in the nonlinear regime."],["dc.description.sponsorship","Open-Access-Publikationsfonds 2013"],["dc.identifier.doi","10.1088/1367-2630/15/2/023017"],["dc.identifier.eissn","1367-2630"],["dc.identifier.fs","602615"],["dc.identifier.isi","000314868000004"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/8720"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/30727"],["dc.language.iso","en"],["dc.notes","47.40.Ki Supersonic and hypersonic flows\r\n\r\n47.27.E- Turbulence simulation and modeling\r\n\r\n47.40.Dc General subsonic flows"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","IOP Publishing"],["dc.relation.issn","1367-2630"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights.uri","http://creativecommons.org/licenses/by-nc-sa/3.0/"],["dc.title","The small-scale dynamo: breaking universality at high Mach numbers"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]