Small-scale dynamo action during the formation of the first stars and galaxies

Schleicher, Dominik R. G.; Banerjee, Rinti; Sur, Sharanya; Arshakian, T. G.; Klessen, Ralf S.; Beck, Rainer; Spaans, Marco

doi:10.1051/0004-6361/201015184

Cited by 188 publications

(182 citation statements)

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“…Due to the efficient magnetic field amplification via the smallscale dynamo, saturation can be expected within a few to a few dozen eddy-turnover times (Kazantsev 1968;Brandenburg & Subramanian 2005;Schleicher et al 2010, Schober et al 2012cBeresnyak 2012). We note here that the presence of the dynamo in supernova-driven turbulence was already demonstrated by Balsara et al (2004) and Balsara & Kim (2005) with numerical simulations.…”

Section: Introductionsupporting

confidence: 57%

A new interpretation of the far-infrared – radio correlation and the expected breakdown at high redshift

Schleicher

Beck

2013

A&A

115

143

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Context. Observations of galaxies up to z ∼ 2 show a tight correlation between far-infrared and radio continuum emission, suggesting a relation between star formation activity and magnetic fields in the presence of cosmic rays. Aims. We explain the far-infrared -radio continuum correlation by relating star formation and magnetic field strength in terms of turbulent magnetic field amplification, where turbulence is injected by supernova explosions from massive stars. We assess the potential evolution of this relation at high redshift, and explore the impact on the far-infrared -radio correlation. Methods. We calculate the expected amount of turbulence in galaxies based on their star formation rates, and infer the expected magnetic field strength due to turbulent dynamo amplification. We calculate the timescales for cosmic ray energy losses via synchrotron emission, inverse Compton scattering, ionization and bremsstrahlung emission, probing up to which redshift strong synchrotron emission can be maintained. Results. We find that the correlation between star formation rate and magnetic field strength in the local Universe can be understood as a result of turbulent magnetic field amplification. The ratio of radio to far-infrared surface brightness is expected to increase with total field strength. A continuation of the correlation is expected towards high redshifts. If the typical gas density in the interstellar medium increases at high z, we expect an increase of the magnetic field strength and the radio emission, as indicated by current observations. Such an increase would imply a modification, but not a breakdown of the far-infrared -radio correlation. We expect a breakdown at the redshift when inverse Compton losses start dominating over synchrotron emission. For a given star formation surface density, we calculate the redshift where the far-infrared -radio correlation will break down, yielding z ∼ (Σ SFR /0.0045 M kpc −2 yr −1 ) 1/(6−α/2) . In this relation, the parameter α describes the evolution of the characteristic ISM density in galaxies as (1 + z) α . We note that observed frequencies of 1−10 GHz are particularly well-suited to explore this relation, as bremsstrahlung losses could potentially dominate at low frequencies. Conclusions. Both the possible raise of the radio emission at high redshift and the final breakdown of the far-infrared -radio correlation at a critical redshift will be probed by the Square Kilometre Array (SKA) and its pathfinders, while the typical ISM density in galaxies will be probed with ALMA. The combined measurements will thus allow a verification of the model proposed here.

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Section: Introductionsupporting

confidence: 57%

A new interpretation of the far-infrared – radio correlation and the expected breakdown at high redshift

Schleicher

Beck

2013

A&A

115

143

View full text Add to dashboard Cite

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“…On theoretical grounds, it is expected that magnetic fields can be efficiently ampified even in small systems and at high redshift, due to the efficient amplification by turbulence (Arshakian et al 2009;Wang & Abel 2009;Schleicher et al 2010;de Souza & Opher 2010;Latif et al 2013;Schober et al 2013), and it is thus conceivable that the far-infrared -radio correlation will be in place early on. As pointed out by Murphy (2009), a potential difficulty is however the increasing strength of the cosmic microwave background at high redshift, enhancing the inverse Compton emission and providing an additional loss mechanism for the cosmic ray electrons.…”

Section: Introductionmentioning

confidence: 99%

Star-forming dwarf galaxies: the correlation between far-infrared and radio fluxes

Schleicher

Beck

2016

A&A

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The far-infrared -radio correlation connects star formation and magnetic fields in galaxies, and has been confirmed over a large range of far-infrared / radio luminosities, both in the local Universe and even at redshifts of z ∼ 2. Recent investigations indicate that it may even hold in the regime of local dwarf galaxies, and we therefore explore here the expected behavior in the regime of star formation surface densities below 0.1 M⊙ kpc −2 yr −1 . We derive two conditions that can be particularly relevant for inducing a change in the expected correlation: a critical star formation surface density to maintain the correlation between star formation rate and the magnetic field, and a critical star formation surface density below which cosmic ray diffusion losses dominate over their injection via supernova explosions. For rotation periods shorter than 1.5 × 10 7 (H/kpc) 2 yrs, with H the scale height of the disk, the first correlation will break down before diffusion losses are relevant, as higher star formation rates are required to maintain the correlation between star formation rate and magnetic field strength. For high star formation surface densities ΣSFR, we derive a characteristic scaling of the non-thermal radio to the far-infrared / infrared emission with Σ 1/3 SFR , corresponding to a scaling of the non-thermal radio luminosity Ls with the infrared luminosity L th as L 4/3 th . The latter is expected to change when the above processes are no longer steadily maintained. In the regime of long rotation periods, we expect a transition towards a steeper scaling with Σ 2/3 SFR , implying Ls ∝ L 5/3th , while the regime of fast rotation is expected to show a considerably enhanced scatter, as a well-defined relation between star formation and magnetic field strength is not maintained. The scaling relations above explain the increasing thermal fraction of the radio emission observed within local dwarfs, and can be tested with future observations by LOFAR as well as the SKA and its precursor radio telescopes.

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“…Such accretion-driven turbulence can amplify weak magnetic seed fields by a process called the small-scale dynamo [12]. For a naive estimate on the potential field amplification, we calculate the eddy-turnover timescale for Kolmogorov and Burgers type turbulence, adopting scaling laws of v ∝ l 1/3 and v ∝ l 1/2 , respectively.…”

Section: Amplification During Gravitational Collapsementioning

confidence: 99%

The role of magnetic fields during primordial star formation

Schleicher¹,

Sur²,

Banerjee³

et al. 2011

Proceedings of Cosmic Radiation Fields: Sources in the Early Universe — PoS(CRF 2010)

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Recent FERMI observations provide a lower limit of 10 −15 G for the magnetic field strength in the intergalactic medium (IGM). This is consistent with theoretical expectations based on the Biermann battery effect, which predicts such IGM fields already at redshifts z ∼ 10. During gravitational collapse, such magnetic fields can be amplified by compression and by turbulence, giving rise to the small-scale dynamo. On scales below the Jeans length, the eddy turnover timescale is much shorter than the free-fall timescale, so that saturation can be reached during collapse. This scenario has been tested and confirmed with magneto-hydrodynamical simulations following the collapse of a turbulent, weakly magnetized cloud. Based on a spectral analysis, we confirm that turbulence is injected on the Jeans scale. For the power spectrum of the magnetic field, we obtain the Kazantsev slope which is characteristic for the small-scale dynamo. A calculation of the critical length scales for ambipolar diffusion and Ohmic dissipation shows that these scales are always small enough to allow significant amplification of the magnetic field by small-scale eddies. We discuss potential implications for the protostellar accretion disk, with particular focus on the magneto-rotational instability, which may change the morphology of the disk and reduce the accretion rate by a factor of a few. Universe -CRF2010, November 9-12, 2010 Desy Germany * Speaker. Magnetic fields during primordial star formation Dominik R. G. Schleicher Cosmic Radiation Fields: Sources in the early The initial field strength: Upper and lower limitsAn observational lower limit on the magnetic field strength in the intergalactic medium (IGM) has been derived based on recent FERMI observations of TeV blazars [1,2,3]. For such blazars, the TeV flux is known, and the expected GeV flux can be calculated by modeling the cascade of the high-energy particles. The expected flux is however orders of magnitudes higher than the current upper limit obtained with FERMI, unless magnetic fields deflected charged particles from the line of sight. Based on these data, a lower limit of the magnetic field strength can be obtained. In general, this lower limit depends on the assumed coherence length L B [1]. For L B > 0.1 Mpc, the lower limit is of the order 10 −15 G, while for smaller coherence lengths, the lower limits increases as L −0.5 B . As shown in [3], this IGM field fills more than 60% of the volume. This observational constraint is consistent with theoretical expectations based on the Biermann battery term [4]. In a cosmological MHD simulation, the generation of magnetic fields was followed based on the Biermann battery effect [5], finding IGM magnetic fields of 10 −15 G at z ∼ 10, which may naturally explain the observed lower limits. Additional seed fields may be created by the Weibel instability in shocks [6]. Even stronger magnetic fields may have been created in the Universe before recombination [7,8]. For such cases, an upper limit of ∼ 3 nG (co-moving) has been derived f...

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Small-scale dynamo action during the formation of the first stars and galaxies

Cited by 188 publications

References 79 publications

A new interpretation of the far-infrared – radio correlation and the expected breakdown at high redshift

A new interpretation of the far-infrared – radio correlation and the expected breakdown at high redshift

Star-forming dwarf galaxies: the correlation between far-infrared and radio fluxes

The role of magnetic fields during primordial star formation

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