arXiv subjects

Dominik R. G. Schleicher

Publications and source records attributed to Dominik R. G. Schleicher.

At least 37 records · Page 2Linked to original sources

arXiv2022

Origin of eclipsing time variations in Post-Common-Envelope binaries: role of the centrifugal force

Eclipsing time variations (ETVs) in post-common-envelope binaries (PCEBs) were proposed to be due to the time-varying component of the stellar gravitational quadrupole moment. This is suggested to be produced by changes in the stellar structure due to an internal redistribution of angular momentum and the effect of the centrifugal force. We examined this hypothesis and present 3D simulations of compressible magnetohydrodynamics (MHD) performed with the {\sc Pencil Code}. We modeled the stellar dynamo for a solar-mass star with angular velocities of 20 and 30 times solar. We included and varied the strength of the centrifugal force and compared the results with reference simulations without the centrifugal force and with a simulation in which its effect is enhanced. The centrifugal force causes perturbations in the evolution of the numerical model, so that the outcome in the details becomes different as a result of nonlinear evolution. While the average density profile is unaffected by the centrifugal force, a relative change in the density difference between high latitudes and the equator of $\sim10^{-4}$ is found. The power spectrum of the convective velocity is found to be more sensitive to the angular velocity than to the strength of the centrifugal force. The quadrupole moment of the stars includes a fluctuating and a time-independent component, which vary with the rotation rate. As very similar behavior is produced in absence of the centrifugal force, we conclude that it is not the main ingredient for producing the time-averaged and fluctuating quadrupole moment of the star. In a real physical system, we thus expect contributions from both components, that is, from the time-dependent gravitational force from the variation in the quadrupole term and from the spin-orbit coupling that is due to the persistent part of the quadrupole.

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arXiv2022

Simulations of fully convective M dwarfs: dynamo action with varying magnetic Prandtl numbers

M dwarfs are low-mass main-sequence stars, the most numerous type of stars in the solar neighbourhood, which are known to have significant magnetic activity. The aim of this work is to explore the dynamo solutions and magnetic fields of fully convective M dwarfs with varying magnetic Prandtl numbers ${\rm Pr_M}$, and a rotation period (${\rm P_{rot}}$) of 43 days. ${\rm Pr_M}$ is known to play an important role in the dynamo action; dynamos for low-$\rm Pr_M$ and large-$\rm Pr_M$ have very different properties. We performed three-dimensional magnetohydrodynamical (MHD) numerical simulations with the ``star-in-a-box'' model using stellar parameters for an M5 dwarf with $0.21 M_{\odot}$. We found that the dynamo solutions are sensitive to ${\rm Pr_M}$. The simulations at this rotation period present periodic cycles of the large-scale magnetic field up to ${\rm Pr_M} \leq 2$; for higher values the cycles disappear and irregular solutions to arise. Our results are consistent with previous studies and suggest that the dynamos operating in fully convective stars behave similarly as those in partially convective stars.

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arXiv2022

Synthetic observations using POLARIS: an application to simulations of massive prestellar cores

Young massive stars are usually found embedded in dense and massive molecular clumps which are known for being highly obscured and distant. During their formation process, the degree of deuteration can be used as a potential indicator of the very early formation stages. This is particularly effective when employing the abundance of H$_2$D$^+$. However, its low abundances and large distances make detections in massive sources hard to achieve. We present an application of the radiative transfer code POLARIS, with the goal to test the observability of the ortho-H$_2$D$^+$ transition $1_{10}$-$1_{11}$ (372.42 GHz) using simulations of high-mass collapsing cores that include deuteration chemistry. We analyzed an early and a late stage of the collapse of a 60 M$_{\odot}$ core, testing different source distances. For all cases, we generated synthetic single-dish and interferometric observations and studied the differences in both techniques. The column densities we derive are comparable to values reported for similar sources. These estimates depend on the extent over which they are averaged, and sources with compact emission they can be highly affected by beam dilution. Combined ALMA-ACA observations improve in signal-to-noise ratio and lead to better column density estimates as compared to ALMA alone. We confirm the feasibility to study ortho-H$_2$D$^+$ emission up to distances of 7 kpc. We provide a proof-of-concept of our framework for synthetic observations and highlight its importance when comparing numerical simulations with real observations. This work also proves how relevant it is to combine single-dish and interferometric measurements to derive appropriate source column densities.

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arXiv2022

The Fermi paradox: Impact of astrophysical processes and dynamical evolution

The Fermi paradox has given rise to various attempts to explain why no evidence of extraterrestrial civilisations was found so far on Earth and in our Solar System. Here, we present a dynamical model for the development of such civilisations, which accounts for self-destruction, colonisation and astrophysical destruction mechanisms of civilisations including gamma-ray bursts, type Ia and type II supernovae as well as radiation from the supermassive black hole. We adopt conservative estimates regarding the efficiency of such processes and find that astrophysical effects can influence the development of intelligent civilisations and change the number of systems with such civilisations by roughly a factor of 2; potentially more if the feedback is enhanced. Our results show that non-equilibrium evolution allows for solutions in-between extreme cases such as "rare Earth" or extreme colonisation, including scenarios with civilisation fractions between 10^{-2} and 10^{-7}. These would imply still potentially large distances to the next such civilisations, particularly when persistence phenomena are being considered. As previous studies, we confirm that the main uncertainties are due to the lifetime of civilisations as well as the assumed rate of colonisation. For SETI-like studies, we believe that unbiased searches are needed considering both the possibilities that the next civilisations are nearby or potentially very far away.

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arXiv2022

Origin of eclipsing time variations: Contributions of different modes of the dynamo-generated magnetic field

The possibility to detect circumbinary planets and to study stellar magnetic fields through eclipsing time variations (ETVs) in binary stars has sparked an increase of interest in this area of research. We revisit the connection between stellar magnetic fields and the gravitational quadrupole moment $Q_{xx}$ and compare different dynamo-generated ETV models with our simulations. We present magnetohydrodynamical simulations of solar mass stars with rotation periods of 8.3, 1.2, and 0.8 days and perform a detailed analysis of the magnetic and quadrupole moment using spherical harmonic decomposition. The extrema of $Q_{xx}$ are associated with changes in the magnetic field structure. This is evident in the simulation with a rotation period of 1.2 days. Its magnetic field has a more complex behavior than in the other models, as the large-scale nonaxisymmetric field dominates throughout the simulation and the axisymmetric component is predominantly hemispheric. This triggers variations in the density field that follow the magnetic field asymmetry with respect to the equator, affecting the $zz$ component of the inertia tensor, and thus modulating $Q_{xx}$. The magnetic field of the two other runs are less variable in time and more symmetric with respect to the equator, such that the variations in the density are weaker, and therefore only small variations in $Q_{xx}$ are seen. If interpreted via the classical Applegate mechanism (tidal locking), the quadrupole moment variations obtained in the current simulations are about two orders of magnitude below those deduced from observations of post-common-envelope binaries. However, if no tidal locking is assumed, our results are compatible with the observed ETVs.

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arXiv2021

General relativistic radiation transport: Implications for VLBI/EHT observations of AGN discs, winds and jets

In 2019, the Event Horizon Telescope Collaboration (EHTC) has published the first image of a supermassive black hole (SMBH) obtained via the Very Large Baseline Interferometry (VLBI) technique. In the future, it is expected that additional and more sensitive VLBI observations will be pursued for other nearby Active Galactic Nuclei (AGN), and it is therefore important to understand which possible features can be expected in such images. In this paper, we post-process General Relativistic Magneto-Hydrodynamical (GR-MHD) simulations which include resistivity, thus providing a self-consistent jet formation model, including resistive mass loading of a wind launched from a disc in Keplerian rotation. The ray-tracing is done using the General Relativistic Ray-Tracing code GRTRANS assuming synchrotron emission. We study the appearance of the black hole environment including the accretion disc, winds and jets under a large range of condition, varying black hole mass, accretion rate, spin, inclination angle, disc parameters and observed frequency. When we adopt M87-like parameters, we show that we can reproduce a ring-like feature (similar as observed by the EHT) for some of our simulations. The latter suggests that such Keplerian disc models thus could be consistent with the observed results. Depending on their masses, accretion rates, spin and the sensitivity of the observation, we note that other SMBHs may show additional features like winds and jets in the observations.

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arXiv2021

Turbulence and its connection to episodic accretion in binary YSOs

We report signatures of episodic accretion in young stellar objects (YSOs) that emerge in protobinary configurations in a gravoturbulent gas collapse. We find in most of these protobinary systems strong accretion bursts between the two companions with a recurrence time-scale of about 1 kyr. The accretion rate onto the secondary star typically exceeds that onto the primary with a peak value of 2 $\times 10^{-2}$ M$_{\odot}$ yr$^{-1}$ for the former and 6 $\times 10^{-3}$ M$_{\odot}$ yr$^{-1}$ for the latter. We propose that the secondary companion which remains more active in its episodes of accretion bursts, especially for the gas cores with subsonic velocity dispersion, may provide observational opportunities to find traces of episodic accretion in the surrounding gas of the embedded YSOs that are in a binary configuration. Also, protostars evolving as single objects in the same environment show fewer accretion bursts and all together a more steady mass growth history. The prestellar cores with subsonic velocity dispersion exhibit an order of magnitude more intense accretion bursts than in the case of cores with supersonic velocity dispersions. The latter shows the formation of some of the protobinaries in which the primary acts as a more actively accreting companion. This can support these binaries to become systems of extreme mass ratio. Moreover, the YSOs in binary configurations with small semi-major axis $a$ $\approx$ 50 au and high mass ratio $q$ > 0.7 support phases of intense episodic accretion. The eccentricity, however, seems to play no significant role in the occurrence of accretion bursts.

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arXiv2021

Chemical analysis of prestellar cores in Ophiuchus yields short timescales and rapid collapse

Sun-like stars form from the contraction of cold and dense interstellar clouds. How the collapse proceeds and what are the main physical processes driving it, however, is still under debate and a final consensus on the timescale of the process has not been reached. Does this contraction proceed slowly, sustained by strong magnetic fields and ambipolar diffusion, or is it driven by fast collapse with gravity dominating the entire process? One way to answer this question is to measure the age of prestellar cores through statistical methods based on observations or via reliable chemical chronometers, which should better reflect the physical conditions of the cores. Here we report APEX observations of ortho-H$_2$D$^+$ and para-D$_2$H$^+$ for six cores in the Ophiuchus complex and combine them with detailed three-dimensional magneto-hydrodynamical simulations including chemistry, providing a range of ages for the observed cores up to 200 kyr. The outcome of our simulations and subsequent analysis provides a good match with the observational results in terms of physical (core masses and volume densities) and dynamical parameters such as the Mach number and the virial parameter. We show that models of fast collapse successfully reproduce the observed range of chemical abundance ratios as the timescales to reach the observed stages is comparable to the dynamical time of the cores (i.e. the free-fall time) and much shorter than the ambipolar diffusion time, measured from the electron fraction in the simulations. To confirm that this ratio can be used to distinguish between different star-formation scenarios a larger (statistically relevant) sample of star-forming cores should be explored.

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arXiv2021

Formation of supermassive black hole seeds in nuclear star clusters via gas accretion and runaway collisions

More than two hundred supermassive black holes (SMBHs) of masses $\gtrsim 10^9\,\mathrm{M_{\odot}}$ have been discovered at $z \gtrsim 6$. One promising pathway for the formation of SMBHs is through the collapse of supermassive stars (SMSs) with masses $\sim 10^{3-5}\,\mathrm{M_{\odot}}$ into seed black holes which could grow upto few times $10^9\,\mathrm{M_{\odot}}$ SMBHs observed at $z\sim 7$. In this paper, we explore how SMSs with masses $\sim 10^{3-5}\,\mathrm{M_{\odot}}$ could be formed via gas accretion and runaway stellar collisions in high-redshift, metal-poor nuclear star clusters (NSCs) using idealised N-body simulations. We explore physically motivated accretion scenarios, e.g. Bondi-Hoyle-Lyttleton accretion and Eddington accretion, as well as simplified scenarios such as constant accretions. While gas is present, the accretion timescale remains considerably shorter than the timescale for collisions with the most massive object (MMO). However, overall the timescale for collisions between any two stars in the cluster can become comparable or shorter than the accretion timescale, hence collisions still play a crucial role in determining the final mass of the SMSs. We find that the problem is highly sensitive to the initial conditions and our assumed recipe for the accretion, due to the highly chaotic nature of the problem. The key variables that determine the mass growth mechanism are the mass of the MMO and the gas reservoir that is available for the accretion. Depending on different conditions, SMSs of masses $\sim10^{3-5} \,\mathrm{M_{\odot}}$ can form for all three accretion scenarios considered in this work.

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arXiv2021

Effect of mass loss due to stellar winds on the formation of supermassive black hole seeds in dense nuclear star clusters

The observations of high redshifts quasars at $z\gtrsim 6$ have revealed that supermassive black holes (SMBHs) of mass $\sim 10^9\,\mathrm{M_{\odot}}$ were already in place within the first $\sim$ Gyr after the Big Bang. Supermassive stars (SMSs) with masses $10^{3-5}\,\mathrm{M_{\odot}}$ are potential seeds for these observed SMBHs. A possible formation channel of these SMSs is the interplay of gas accretion and runaway stellar collisions inside dense nuclear star clusters (NSCs). However, mass loss due to stellar winds could be an important limitation for the formation of the SMSs and affect the final mass. In this paper, we study the effect of mass loss driven by stellar winds on the formation and evolution of SMSs in dense NSCs using idealised N-body simulations. Considering different accretion scenarios, we have studied the effect of the mass loss rates over a wide range of metallicities $Z_\ast=[.001-1]\mathrm{Z_{\odot}}$ and Eddington factors $f_{\rm Edd}=L_\ast/L_{\mathrm{Edd}}=0.5,0.7,\,\&\, 0.9$. For a high accretion rate of $10^{-4}\,\mathrm{M_{\odot}yr^{-1}}$, SMSs with masses $\gtrsim 10^3\MSun$ could be formed even in a high metallicity environment. For a lower accretion rate of $10^{-5}\,\mathrm{M_{\odot}yr^{-1}}$, SMSs of masses $\sim 10^{3-4}\,\mathrm{M_{\odot}}$ can be formed for all adopted values of $Z_\ast$ and $f_{\rm Edd}$, except for $Z_\ast=\mathrm{Z_{\odot}}$ and $f_{\rm Edd}=0.7$ or 0.9. For Eddington accretion, SMSs of masses $\sim 10^3\,\mathrm{M_{\odot}}$ can be formed in low metallicity environments with $Z_\ast\lesssim 0.01\mathrm{Z_{\odot}}$. The most massive SMSs of masses $\sim 10^5\,\mathrm{M_{\odot}}$ can be formed for Bondi-Hoyle accretion in environments with $Z_\ast \lesssim 0.5\mathrm{Z_{\odot}}$.

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arXiv2021

Magnetic field amplification in accretion discs around the first stars: implications for the primordial IMF

Magnetic fields play an important role in the dynamics of present-day molecular clouds. Recent work has shown that magnetic fields are equally important for primordial clouds, which form the first stars in the Universe. While the primordial magnetic field strength on cosmic scales is largely unconstrained, theoretical models strongly suggest that a weak seed field existed in the early Universe. We study how the amplification of such a weak field can influence the evolution of accretion discs around first stars, and thus affect the primordial initial mass function (IMF). We perform a suite of 3D ideal magneto-hydrodynamic (MHD) simulations with different initial field strengths and numerical resolutions. We find that, in simulations with sufficient spatial resolution to resolve the Jeans scale during the collapse, even initially weak magnetic fields grow exponentially to become dynamically important due to both the so-called 'small-scale turbulent dynamo' and the 'large-scale mean-field dynamo'. Capturing the small-scale dynamo action depends primarily on how well we resolve the Jeans length, while capturing the large-scale dynamo depends on the Jeans resolution as well as the maximum absolute resolution. Provided enough resolution, we find that fragmentation does not depend strongly on the initial field strength, because even weak fields grow to become strong. However, fragmentation in runs with magnetic fields differs significantly from those without magnetic fields. We conclude that the development of dynamically strong magnetic fields during the formation of the first stars is likely inevitable, and that these fields had a significant impact on the primordial IMF.

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arXiv2020

Stellar Initial Mass Function over a range of redshifts

The stellar Initial Mass Function (IMF) seems to be close to universal in the local star-forming regions. However, this quantity of a newborn stellar population responds differently at gas metallicities $Z \sim$ $Z_\odot$ than $Z$ = 0. A view on the cosmic star formation history suggests that the cooling agents in the gas vary both in their types and molecular abundances. For instance, in the primordial gas environment, the gas temperature can be higher by a factor of 30 as compared to the present day. Stellar radiation feedback and cosmic microwave background (CMB) radiation may even contribute towards increasing the floor temperature of the star-forming gas which subsequently can leave profound impacts on the IMF. We present the contribution of the radiation sources towards the thermodynamical evolution of the Jeans unstable gas cloud which experiences fragmentation and mass accretion. We find evidence which suggests that the latter becomes the dominant process for star formation efficiencies (SFE) above 5 - 7 %, thus increasing the average mass of the stars. We focus on the isolated and binary stellar configurations emerging during the gas collapse. The binary fraction on average remains 0.476 and contributes significantly towards the total SFE of 15 %.

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arXiv2020

Synthetic observations of deuterated molecules in massive prestellar cores

Young massive stars are usually found embedded in dense massive molecular clumps and are known for being highly obscured and distant. During their formation process, deuteration is regarded as a potentially good indicator of the very early formation stages. In this work, we test the observability of the ground-state transition of ortho-H$_2$D$^+$ $J_{\rm {K_a, K_c}} = 1_{10}$-$1_{11} $ by performing interferometric and single-dish synthetic observations using magneto-hydrodynamic simulations of high-mass collapsing molecular cores, including deuteration chemistry. We studied different evolutionary times and source distances (from 1 to 7 kpc) to estimate the information loss when comparing the column densities inferred from the synthetic observations to the column densities in the model. We mimicked single-dish observations considering an APEX-like beam and interferometric observations using CASA and assuming the most compact configuration for the ALMA antennas. We found that, for centrally concentrated density distributions, the column densities are underestimated by about 51% in the case of high-resolution ALMA observations ($\leqslant$1") and up to 90% for APEX observations (17"). Interferometers retrieve values closer to the real ones, however, their finite spatial sampling results in the loss of contribution from large-scale structures due to the lack of short baselines. We conclude that, the emission of o-H$_2$D$^+$ in distant massive dense cores is faint and would require from $\sim$1 to $\sim$7 hours of observation at distances of 1 and 7 kpc, respectively, to achieve a 14$σ$ detection in the best case scenario. Additionally, the column densities derived from such observations will certainly be affected by beam dilution in the case of single-dishes and spatial filtering in the case of interferometers.

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arXiv2020

A new proxy to estimate the cosmic-ray ionisation rate in dense cores

Cosmic rays are a global source of ionisation, and the ionisation fraction represents a fundamental parameter in the interstellar medium. Ions couple to magnetic fields, affect the chemistry, and the dynamics of star-forming regions as well as planetary atmospheres. However, the cosmic-ray ionisation rate represents one of the bottlenecks for astrochemical models, and its determination is one of the most puzzling problems in astrophysics. While for diffuse clouds reasonable values have been provided from H$_3^+$ observations, for dense clouds, due to the lack of rotational transitions, this is not possible, and estimates are strongly biased by the employed model. We present here an analytical expression, obtained from first principles, to estimate the cosmic-ray ionisation rate from observational quantities. The theoretical predictions are validated with high-resolution three-dimensional numerical simulations and applied to the well known core L1544; we obtained an estimate of $ζ_2 \sim 2-3 \times 10^{-17}$ s$^{-1}$. Our results and the analytical formulae provided represent the first model-independent, robust tool to probe the cosmic-ray ionisation rate in the densest part of star-forming regions (on spatial scales of $R \leq 0.05$ pc). An error analysis is presented to give statistical relevance to our study.

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arXiv2019

Resolving accretion flows in nearby active galactic nuclei with the Event Horizon Telescope

The Event Horizon Telescope (EHT), now with its first ever image of the photon ring around the supermassive black hole of M87, provides a unique opportunity to probe the physics of supermassive black holes through Very Long Baseline Interferometry (VLBI), such as the existence of the event horizon, the accretion processes as well as jet formation in Low Luminosity AGN (LLAGN). We build a theoretical model which includes an Advection Dominated Accretion Flow (ADAF) with emission from thermal and non-thermal electrons in the flow and a simple radio jet outflow. The predicted spectral energy distribution (SED) of this model is compared to sub-arcsec resolution observations to get the best estimates of the model parameters. The model-predicted radial emission profiles at different frequency bands are used to predict whether the inflow can be resolved by the EHT or with telescopes such as the Global 3-mm VLBI array (GMVA). In this work the model is initially tested with high resolution SED data of M87 and then applied to our sample of 5 galaxies (Cen A, M84, NGC 4594, NGC 3998 and NGC 4278). The model then allows us to predict if one can detect and resolve the inflow for any of these galaxies using the EHT or GMVA within an 8 hour integration time.

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arXiv2019

Magneto-hydrodynamical origin of eclipsing time variations in post-common-envelope binaries for solar mass secondaries

Eclipsing time variations have been observed for a wide range of binary systems, including post-common-envelope binaries. A frequently proposed explanation, apart from the possibility of having a third body, is the effect of magnetic activity, which may alter the internal structure of the secondary star, particularly its quadrupole moment, and thereby cause quasi-periodic oscillations. Here we present two compressible non-ideal magneto-hydrodynamical (MHD) simulations of the magnetic dynamo in a solar mass star, one of them with three times the solar rotation rate ("slow rotator"), the other one with twenty times the solar rotation rate ("rapid rotator"), to account for the high rotational velocities in close binary systems. For the slow rotator, we find that both the magnetic field and the stellar quadrupole moment change in a quasi-periodic manner, leading to O-C (observed - corrected times of the eclipse) variations of ~0.025 s. For the rapid rotator, the behavior of the magnetic field as well as the quadrupole moment changes become considerably more complex, due to the less coherent dynamo solution. The resulting O-C variations are of the order 0.13 s. The observed system V471~Tau shows two modes of eclipsing time variations, with amplitudes of 151 s and 20 s, respectively. However, the current simulations may not capture all relevant effects due to the neglect of the centrifugal force and self-gravity. Considering the model limitations and that the rotation of V471 Tau is still a factor of 2.5 faster than our rapid rotator, it may be conceivable to reach the observed magnitudes.

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arXiv2019

Discovery of a nitrogen-enhanced mildly metal-poor binary system: Possible evidence for pollution from an extinct AGB Star

We report the serendipitous discovery of a nitrogen-rich, mildly metal-poor ([Fe/H]=-1.08) giant star in a single-lined spectroscopic binary system found in the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) survey, Data Release 14 (DR14). Previous work has assumed that the two percent of halo giants with unusual elemental abundances have been evaporated from globular clusters, but other origins for their abundance signatures, including binary mass transfer, must also be explored. We present the results of an abundance re-analysis of the APOGEE-2 high-resolution near-infrared spectrum of 2M12451043+1217401 with the Brussels Automatic Stellar Parameter (BACCHUS) automated spectral analysis code, and re-derive manually the main element families, namely the light elements (C, N), elements (O, Mg, Si), iron-peak element (Fe), \textit{s}-process element (Ce), and the light odd-Z element (Al). Our analysis confirm the N-rich nature of 2M12451043+1217401, which has a [N/Fe] ratio of $+0.69$, and shows that the abundances of C and Al are slightly discrepant from that of a typical mildly metal-poor RGB star, but exhibit Mg, Si, O and \textit{s}-process abundances (Ce) of typical field stars. We also detect a particularly large variability in its radial velocity over the period of the APOGEE-2 observations, and the most likely orbit fit to the radial velocity data has a period of $730.89\pm106.86$ days, a velocity semi-amplitude of $9.92 \pm 0.14$ km s$^{-1}$, and an eccentricity of $\sim 0.1276 \pm0.1174$, which support the hypothesis of a binary companion, and that has probably been polluted by a now-extinct AGB star.

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arXiv2019

Intermittent fragmentation and statistical variations during gas collapse in magnetised atomic cooling haloes

Observations reveal the presence of supermassive black holes (SMBH) as early as ~700 million years after the Big Bang. Their formation path is still subject to current debate. We explore the influence of magnetic fields, which are strongly amplified via the turbulent small-scale dynamo, on the formation of SMBH seeds within the direct collapse scenario. In this study, we perform for the first time cosmological magnetohydrodynamic large eddy simulations that employ a model for unresolved, compressible MHD turbulence. In total we perform 36 simulations for 9 haloes each with two different initial magnetic field strengths, and with and without employing the unresolved turbulence model. We make use of the adaptive mesh refinement approach to achieve an effective spatial resolution of less than one proper astronomical unit. We consider a regime where cooling is regulated by atomic hydrogen and the molecular hydrogen gets dissociated by a strong radiation field. Our main finding is that the majority of the gas properties in the haloes at the final output are predominantly determined by the run-away gravitational collapse. Turbulence is supersonic and super-Alfvénic in all cases, and magnetic fields are amplified to an approximately dynamically relevant regime. Finally, fragmentation during the collapse is intermittent and mass accretion rates range from 0.2-3 Msun/yr. This suggests that the presence of strongly amplified magnetic fields and turbulence provides additional pressure support on small scales and make the direct collapse a viable scenario for the formation of massive objects under the required ambient conditions.

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