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Schleicher D.R.G.,ESO Garching | Banerjee R.,University of Heidelberg | Sur S.,University of Heidelberg | Glover S.C.O.,University of Heidelberg | And 3 more authors.
AIP Conference Proceedings | Year: 2010

We discuss the formation of supermassive black holes in the early universe, and how to probe their subsequent evolution with the upcoming mm/sub-mm telescope ALMA. We first focus on the chemical and radiative conditions for black hole formation, in particular considering radiation trapping and molecular dissociation effects. We then turn our attention towards the magnetic properties in the halos where the first black holes form, and show that the presence of turbulence may lead to a magnetic dynamo, which could support the black hole formation process by providing an efficient means of transporting the angular momentum.We finally focus on observable properties of high-redshift black holes with respect to ALMA, and discuss how to distinguish between chemistry driven by the starburst and chemistry driven by X-rays from the black hole. © 2010 American Institute of Physics. Source

Schleicher D.R.G.,ESO Garching | Banerjee R.,University of Heidelberg | Glover S.C.O.,University of Heidelberg | Galli D.,National institute for astrophysics | And 4 more authors.
AIP Conference Proceedings | Year: 2010

We discuss possible implications of strong primordial magnetic fields, which may have been created during cosmic inflation or the QCD / electroweak phase transition, and explore how they influence the epoch of reionization and primordial star formation. Globally, magnetic fields may delay reionization, as the magnetic pressure suppresses gravitational collapse in small halos. In the protostellar collapse phase, we find that ambipolar diffusion heating does not change the fragmentation mass scale significantly, but may enhance the accretion rate at higher densities. © 2010 American Institute of Physics. Source

Sur S.,University of Heidelberg | Schleicher D.R.G.,ESO Garching | Schleicher D.R.G.,Leiden University | Banerjee R.,University of Heidelberg | And 3 more authors.
Astrophysical Journal Letters | Year: 2010

Cosmological hydrodynamical simulations of primordial star formation suggest that the gas within the first starforming halos is turbulent. This has strong implications on the subsequent evolution, in particular on the generation of magnetic fields. Using high-resolution numerical simulations, we show that in the presence of turbulence, weak seed magnetic fields are exponentially amplified by the small-scale dynamo during the formation of the first stars. We conclude that strong magnetic fields are generated during the birth of the first stars in the universe, potentially modifying the mass distribution of these stars and influencing the subsequent cosmic evolution. We find that the presence of the small-scale turbulent dynamo can only be identified in numerical simulations in which the turbulent motions in the central core are resolved with at least 32 grid cells. © 2010. The American Astronomical Society. All rights reserved. Source

Schleicher D.R.G.,ESO Garching | Spaans M.,Leiden University | Glover S.C.O.,University of Groningen | Glover S.C.O.,University of Heidelberg
Astrophysical Journal Letters | Year: 2010

In massive primordial galaxies, the gas may directly collapse and form a single central massive object if cooling is suppressed. H2 line cooling can be suppressed in the presence of a strong soft-ultraviolet radiation field, but the role played by other cooling mechanisms is less clear. In optically thin gas, Lyα cooling can be very effective, maintaining the gas temperature below 104 K over many orders of magnitude in density. However, the large neutral hydrogen column densities present in primordial galaxies render them highly optically thick to Lyα photons. In this paper, we examine in detail the effects of the trapping of these Lyα photons on the thermal and chemical evolution of the gas. We show that despite the high optical depth in the Lyman series lines, cooling is not strongly suppressed, and proceeds via other atomic hydrogen transitions. At densities larger than ∼ 109 cm-3, collisional dissociation of molecular hydrogen becomes the dominant cooling process and decreases the gas temperature to about 5000 K. The gas temperature evolves with density as T α ρ γ eff -1, with γeff = 0.97-0.98. The evolution is thus very close to isothermal, and so fragmentation is possible, but unlikely to occur during the initial collapse. However, after the formation of a massive central object, we expect that later-infalling, higher angular momentum material will form an accretion disk that may be unstable to fragmentation, which may give rise to star formation with a top-heavy initial mass function. © 2010. The American Astronomical Society. All rights reserved. Source

Wittkowski M.,ESO Garching | Arroyo-Torres B.,DIPC | Marcaide J.M.,University of Valencia | Abellan F.J.,University of Nice Sophia Antipolis | And 4 more authors.
Proceedings of the International Astronomical Union | Year: 2014

We present near-infrared spectro-interferometric studies of red supergiant (RSG) stars using the VLTI/AMBER instrument, which are compared to previously obtained similar observations of AGB stars. Our observations indicate spatially extended atmospheric molecular layers of water vapor and CO, similar as previously observed for Mira stars. Data of VY∼CMa indicate that the molecular layers are asymmetric, possibly clumpy. Thanks to the spectro-interferometric capabilities of the VLTI/AMBER instrument, we can isolate continuum bandpasses, estimate fundamental parameters of our sources, locate them in the HR diagram, and compare their positions to recent evolutionary tracks. For the example of VY CMa, this puts it close to evolutionary tracks of initial mass 25-32 M S™. Comparisons of our data to hydrostatic model atmospheres, 3d simulations of convection, and 1d dynamic model atmospheres based on self-excited pulsation models indicate that none of these models can presently explain the observed atmospheric extensions for RSGs. The mechanism that levitates the atmospheres of red supergiant is thus a currently unsolved problem. Copyright © International Astronomical Union 2015. Source

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