The Small-Scale Dynamo and Non-Ideal Magnetohydrodynamics in Primordial Star Formation

Schober, Jennifer; Schleicher, Dominik R. G.; Federrath, Christoph; Glover, Simon C. O.; Klessen, Ralf S.; Banerjee, Rinti

doi:10.1088/0004-637x/754/2/99

Cited by 154 publications

(168 citation statements)

References 69 publications

(103 reference statements)

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“…The latter will ensure magnetic field amplification via the small-scale dynamo (e.g. Kazantsev 1968;Schekochihin et al 2002;Schober et al 2012), which happens on short timescales and effectively ensures that the magnetic field strength is coupled to the star formation rate. Considering a typical size of the star-forming region of 1 kpc, this relation will break down at critical star formation surface densities of 10 −5 − 10 −6 M ⊙ kpc −2 yr −1 depending on the amount of rotation.…”

Section: Discussionmentioning

confidence: 99%

“…In addition, the supernova explosions of massive stars inject both cosmic rays and turbulence into the interstellar medium. Such turbulence efficiently amplifies magnetic field via the small-scale dynamo (Kazantsev 1968;Subramanian 1999;Schekochihin et al 2002;Schober et al 2012;Federrath et al 2011;Grete et al 2015), and as a result, the feedback from star formation provides the relevant ingredients to drive the radio emission (see e.g. Groves et al 2003;Schleicher & Beck 2013).…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 99%

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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“…We note that the gas out of which the first stars form was likely to be strongly magnetised. Any pre-existing magnetic field was amplified to dynamically significant levels by the small-scale turbulent dynamo which converts parts of the kinetic energy associated with the accretion flow in the star-forming parts of the halo into magnetic energy Sur et al 2010;Schober et al 2012). In principle, magnetic fields can remove angular momentum from the system by magnetic braking (e.g.…”

Section: Lithiummentioning

confidence: 99%

TOPoS

Bonifacio

Caffau

Spite

et al. 2015

A&A

170

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Context. In the course of the Turn Off Primordial Stars (TOPoS) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. These stars are very common among the stars of extremely low metallicity and provide important clues to the star formation processes. We here present our analysis of six CEMP stars. Aims. We want to provide the most complete chemical inventory for these six stars in order to constrain the nucleosynthesis processes responsible for the abundance patterns. Methods. We analyse both X-Shooter and UVES spectra acquired at the VLT. We used a traditional abundance analysis based on OSMARCS 1D local thermodynamic equilibrium (LTE) model atmospheres and the turbospectrum line formation code. were not able to detect any iron lines, yet we could place a robust (3σ) upper limit of [Fe/H] < −5.0 and measure the Ca abundance, with [Ca/H] = −5.0, and carbon, A(C) = 6.90, suggesting that this star could be even more metal-poor than SDSS J1742+2531. This makes these two stars the seventh and eighth stars known so far with [Fe/H] < −4.5, usually termed ultra-iron-poor (UIP) stars. No lithium is detected in the spectrum of SDSS J1742+2531 or SDSS J1035+0641, which implies a robust upper limit of A(Li) < 1.8 for both stars. Conclusions. Our measured carbon abundances confirm the bimodal distribution of carbon in CEMP stars, identifying a high-carbon band and a low-carbon band. We propose an interpretation of this bimodality according to which the stars on the high-carbon band are the result of mass transfer from an AGB companion, while the stars on the low-carbon band are genuine fossil records of a gas Article published by EDP Sciences A28, page 1 of 20 A&A 579, A28 (2015) cloud that has also been enriched by a faint supernova (SN) providing carbon and the lighter elements. The abundance pattern of the UIP stars shows a large star-to-star scatter in the [X/Ca] ratios for all elements up to aluminium (up to 1 dex), but this scatter drops for heavier elements and is at most of the order of a factor of two. We propose that this can be explained if these stars are formed from gas that has been chemically enriched by several SNe, that produce the roughly constant [X/Ca] ratios for the heavier elements, and in some cases the gas has also been polluted by the ejecta of a faint SN that contributes the lighter elements in variable amounts. The absence of lithium in four of the five known unevolved UIP stars can be explained by a dominant role of fragmentation in the formation of these stars. This would result either in a destruction of lithium in the pre-main-sequence phase, through rotational mixing or to a lack of late accretion from a reservoir of fresh gas. The phenomenon should have varying degrees of efficiency.

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“…The minimum magnetic Reynolds number for the dynamo to operate is about Rm crit ∼ 100; for details see Brandenburg & Subramanian (2005) and Schober et al (2012b). Both the Ohmic and ambipolar resistivity during primordial star formation are found to be sufficiently low to stop efficient magnetic field amplification (Schober et al 2012a). The amplification time corresponds to the timescale of turbulent fluctuations, and is therefore much shorter than the evolutionary timescale of the system.…”

Section: Introductionmentioning

confidence: 99%

Magnetic fields in primordial accretion disks

Latif

Schleicher

2016

A&A

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Magnetic fields are considered a vital ingredient of contemporary star formation and may have been important during the formation of the first stars in the presence of an efficient amplification mechanism. Initial seed fields are provided via plasma fluctuations and are subsequently amplified by the small-scale dynamo, leading to a strong, tangled magnetic field. We explore how the magnetic field provided by the small-scale dynamo is further amplified via the α-Ω dynamo in a protostellar disk and assess its implications. For this purpose, we consider two characteristic cases, a typical Pop. III star with 10 M and an accretion rate of 10 −3 M yr −1 , and a supermassive star with 10 5 M and an accretion rate of 10 −1 M yr −1 . For the 10 M Pop. III star, we find that coherent magnetic fields can be produced on scales of at least 100 AU, which are sufficient to drive a jet with a luminosity of 100 L and a mass outflow rate of 10 −3.7 M yr −1 . For the supermassive star, the dynamical timescales in its environment are even shorter, implying smaller orbital timescales and an efficient magnetization out to at least 1000 AU. The jet luminosity corresponds to ∼10 6.0 L and a mass outflow rate of 10 −2.1 M yr −1 . We expect that the feedback from the supermassive star can have a relevant impact on its host galaxy.

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The Small-Scale Dynamo and Non-Ideal Magnetohydrodynamics in Primordial Star Formation

Cited by 154 publications

References 69 publications

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

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

TOPoS

Magnetic fields in primordial accretion disks

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