scholarly journals Deviations from tidal torque theory: Evolution of the halo spin–filament alignment

2021 ◽  
Vol 502 (4) ◽  
pp. 5528-5545 ◽  
Author(s):  
Pablo López ◽  
Marius Cautun ◽  
Dante Paz ◽  
Manuel Merchán ◽  
Rien van de Weygaert
Keyword(s):  
Initial Conditions ◽  
High Redshift ◽  
Major Change ◽  
Major Axis ◽  
Clear Correlation ◽  
Late Time ◽  
Spin Orientation ◽  
Subsequent Evolution ◽  
Tidal Torque ◽  
Spin Direction

ABSTRACT The alignment between halo spins and the cosmic web is still poorly understood despite being a widely studied topic. Here, we study this alignment within the context of tidal torque theory (TTT) and deviations from it. To this end, we analyse the evolution of the shape and spin direction of proto-haloes, i.e. of all the volume elements associated to a z = 0 halo, with respect to the present-day filaments. We find that the major axis of proto-haloes undergoes a major change, from being strongly perpendicular to the filament spine in the initial conditions, to being preferentially aligned at the present time. In comparison, the spin orientation shows only a mild evolution: it starts slightly parallel to the filament spine, but the subsequent evolution, up to z ∼ 1, gradually changes its orientation to preferentially perpendicular. In order to analyse these signals in the TTT framework, we split the haloes according to their net spin growth with respect to the median TTT expectation, finding a clear correlation with the spin–filament alignment. At the present time, haloes whose spin grew the most are the ones most perpendicular to the filament spine, while haloes whose spin grew below the median TTT expectation are typically more aligned. The dependence of spin directions on net spin growth is already present in the initial conditions, and gets further modified by late-time, z < 2, evolution. Also, spin directions mildly deviate from the TTT predictions even at high redshift, indicating the need for extensions to the model.

scholarly journals Linking gas and particle ejection dynamics to boundary conditions in scaled shock-tube experiments

2021 ◽  
Vol 83 (8) ◽  
Author(s):  
Valeria Cigala ◽  
Ulrich Kueppers ◽  
Juan José Peña Fernández ◽  
Donald B. Dingwell
Keyword(s):  
Particle Size ◽  
Shock Tube ◽  
Initial Conditions ◽  
Volcanic Eruptions ◽  
Tube Length ◽  
Experimental Investigations ◽  
Clear Correlation ◽  
Angular Deviation ◽  
Dynamic Nature ◽  
Experimental Conditions

AbstractPredicting the onset, style and duration of explosive volcanic eruptions remains a great challenge. While the fundamental underlying processes are thought to be known, a clear correlation between eruptive features observable above Earth’s surface and conditions and properties in the immediate subsurface is far from complete. Furthermore, the highly dynamic nature and inaccessibility of explosive events means that progress in the field investigation of such events remains slow. Scaled experimental investigations represent an opportunity to study individual volcanic processes separately and, despite their highly dynamic nature, to quantify them systematically. Here, impulsively generated vertical gas-particle jets were generated using rapid decompression shock-tube experiments. The angular deviation from the vertical, defined as the “spreading angle”, has been quantified for gas and particles on both sides of the jets at different time steps using high-speed video analysis. The experimental variables investigated are 1) vent geometry, 2) tube length, 3) particle load, 4) particle size, and 5) temperature. Immediately prior to the first above-vent observations, gas expansion accommodates the initial gas overpressure. All experimental jets inevitably start with a particle-free gas phase (gas-only), which is typically clearly visible due to expansion-induced cooling and condensation. We record that the gas spreading angle is directly influenced by 1) vent geometry and 2) the duration of the initial gas-only phase. After some delay, whose length depends on the experimental conditions, the jet incorporates particles becoming a gas-particle jet. Below we quantify how our experimental conditions affect the temporal evolution of these two phases (gas-only and gas-particle) of each jet. As expected, the gas spreading angle is always at least as large as the particle spreading angle. The latter is positively correlated with particle load and negatively correlated with particle size. Such empirical experimentally derived relationships between the observable features of the gas-particle jets and known initial conditions can serve as input for the parameterisation of equivalent observations at active volcanoes, alleviating the circumstances where an a priori knowledge of magma textures and ascent rate, temperature and gas overpressure and/or the geometry of the shallow plumbing system is typically chronically lacking. The generation of experimental parameterisations raises the possibility that detailed field investigations on gas-particle jets at frequently erupting volcanoes might be used for elucidating subsurface parameters and their temporal variability, with all the implications that may have for better defining hazard assessment.

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

2021 ◽  
Author(s):  
Arpan Das ◽  
Dominik R G Schleicher ◽  
Nathan W C Leigh ◽  
Tjarda C N Boekholt
Keyword(s):  
Black Holes ◽  
Initial Conditions ◽  
High Redshift ◽  
Star Clusters ◽  
Gas Reservoir ◽  
Highly Sensitive ◽  
Stellar Collisions ◽  
Key Variables ◽  
Chaotic Nature ◽  
Gas Accretion

Abstract More than two hundred supermassive black holes (SMBHs) of masses ≳ 109 M⊙ have been discovered at z ≳ 6. One promising pathway for the formation of SMBHs is through the collapse of supermassive stars (SMSs) with masses ∼103 − 5 M⊙ into seed black holes which could grow upto few times 109 M⊙ SMBHs observed at z ∼ 7. In this paper, we explore how SMSs with masses ∼103 − 5 M⊙ 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 ∼103 − 5 M⊙ can form for all three accretion scenarios considered in this work.

scholarly journals EDGE: a new approach to suppressing numerical diffusion in adaptive mesh simulations of galaxy formation

2020 ◽  
Vol 501 (2) ◽  
pp. 1755-1765
Author(s):  
Andrew Pontzen ◽  
Martin P Rey ◽  
Corentin Cadiou ◽  
Oscar Agertz ◽  
Romain Teyssier ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Adaptive Mesh Refinement ◽  
Large Scale ◽  
Initial Conditions ◽  
Dwarf Galaxy ◽  
High Redshift ◽  
Morphological Structure ◽  
Adaptive Mesh ◽  
Numerical Diffusion

ABSTRACT We introduce a new method to mitigate numerical diffusion in adaptive mesh refinement (AMR) simulations of cosmological galaxy formation, and study its impact on a simulated dwarf galaxy as part of the ‘EDGE’ project. The target galaxy has a maximum circular velocity of $21\, \mathrm{km}\, \mathrm{s}^{-1}$ but evolves in a region that is moving at up to $90\, \mathrm{km}\, \mathrm{s}^{-1}$ relative to the hydrodynamic grid. In the absence of any mitigation, diffusion softens the filaments feeding our galaxy. As a result, gas is unphysically held in the circumgalactic medium around the galaxy for $320\, \mathrm{Myr}$, delaying the onset of star formation until cooling and collapse eventually triggers an initial starburst at z = 9. Using genetic modification, we produce ‘velocity-zeroed’ initial conditions in which the grid-relative streaming is strongly suppressed; by design, the change does not significantly modify the large-scale structure or dark matter accretion history. The resulting simulation recovers a more physical, gradual onset of star formation starting at z = 17. While the final stellar masses are nearly consistent ($4.8 \times 10^6\, \mathrm{M}_{\odot }$ and $4.4\times 10^6\, \mathrm{M}_{\odot }$ for unmodified and velocity-zeroed, respectively), the dynamical and morphological structure of the z = 0 dwarf galaxies are markedly different due to the contrasting histories. Our approach to diffusion suppression is suitable for any AMR zoom cosmological galaxy formation simulations, and is especially recommended for those of small galaxies at high redshift.

scholarly journals Implicit large eddy simulation of shock-driven material mixing

2013 ◽  
Vol 371 (2003) ◽  
pp. 20120217 ◽  
Author(s):  
F. F. Grinstein ◽  
A. A. Gowardhan ◽  
J. R. Ristorcelli
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Mixing ◽  
Initial Conditions ◽  
Spatial Scales ◽  
Late Time ◽  
Eddy Simulation ◽  
Geometrical Complexity ◽  
Planar Shock ◽  
Large Eddy ◽  
Implicit Large Eddy Simulation

Under-resolved computer simulations are typically unavoidable in practical turbulent flow applications exhibiting extreme geometrical complexity and a broad range of length and time scales. An important unsettled issue is whether filtered-out and subgrid spatial scales can significantly alter the evolution of resolved larger scales of motion and practical flow integral measures. Predictability issues in implicit large eddy simulation of under-resolved mixing of material scalars driven by under-resolved velocity fields and initial conditions are discussed in the context of shock-driven turbulent mixing. The particular focus is on effects of resolved spectral content and interfacial morphology of initial conditions on transitional and late-time turbulent mixing in the fundamental planar shock-tube configuration.

scholarly journals Can intrinsic alignments of elongated low-mass galaxies be used to map the cosmic web at high redshift?

2019 ◽  
Vol 488 (4) ◽  
pp. 5580-5593 ◽  
Author(s):  
Viraj Pandya ◽  
Joel Primack ◽  
Peter Behroozi ◽  
Avishai Dekel ◽  
Haowen Zhang ◽  
...  
Keyword(s):  
Hubble Space Telescope ◽  
High Redshift ◽  
Major Axis ◽  
Real Space ◽  
Significant Alignment ◽  
The Galaxy ◽  
Nearby Galaxies ◽  
Low Mass ◽  
Hydrodynamical Simulations ◽  
Future Work

ABSTRACT Hubble Space Telescope observations show that low-mass ($M_*=10^9\!-\!10^{10}\, \mathrm{M}_{\odot }$) galaxies at high redshift (z = 1.0–2.5) tend to be elongated (prolate) rather than disky (oblate) or spheroidal. This is explained in zoom-in cosmological hydrodynamical simulations by the fact that these galaxies are forming in cosmic web filaments where accretion happens preferentially along the direction of elongation. We ask whether the elongated morphology of these galaxies allows them to be used as effective tracers of cosmic web filaments at high redshift via their intrinsic alignments. Using mock light cones and spectroscopically confirmed galaxy pairs from the Cosmic Assembly Near-infared Deep Extragalactic Legacy Survey (CANDELS), we test two types of alignments: (1) between the galaxy major axis and the direction to nearby galaxies of any mass and (2) between the major axes of nearby pairs of low-mass, likely prolate, galaxies. The mock light cones predict strong signals in 3D real space, 3D redshift space, and 2D projected redshift space for both types of alignments (assuming prolate galaxy orientations are the same as those of their host prolate haloes), but we do not detect significant alignment signals in CANDELS observations. However, we show that spectroscopic redshifts have been obtained for only a small fraction of highly elongated galaxies, and accounting for spectroscopic incompleteness and redshift errors significantly degrades the 2D mock signal. This may partly explain the alignment discrepancy and highlights one of several avenues for future work.

scholarly journals The X-ray Spectra of High Redshift Quasars

1989 ◽  
Vol 134 ◽  
pp. 161-166
Author(s):  
Claude R. Canizares ◽  
Julia L. White
Keyword(s):  
High Redshift ◽  
Radio Spectrum ◽  
Clear Correlation ◽  
X Rays ◽  
Spectral Parameters ◽  
X Ray ◽  
Systematic Uncertainties ◽  
Two Component ◽  
X Ray Background ◽  
Single Power

We present mean spectral parameters for various ensembles of quasars observed with the Einstein Observatory Imaging Proportional Counter (IPC). Our sample contains 71 optically or radio selected quasars with 0.1 < z < 3.5, Galactic NH < 1021 cm−2, total counts of 30 −500, and IPC gain < 19. Quasars are grouped into ensembles according to radio properties (Flat Radio Spectrum [FRS], Steep Radio Spectrum [SRS] or Radio Quiet [RQ]), and either redshift or X-ray luminosity, lx. We find a clear correlation between radio properties and α. FRS quasars have α∼0.4, SRS quasars have α∼0.7 and RQ quasars have α ∼1–1.4. There is no evidence for a dependence of α on z nor, for the FRS and SRS ensembles, on lx over nearly three decades. FRS quasars with 2.0 < z < 3.5 have just as flat mean spectra as those with low z, implying that a single power law, which is flatter than the canonical one with α ∼ 0.65, continues into the 1–10 keV band (in which the observed softer X-rays were emitted). Unfortunately, the results for high redshift and high lx RQ quasars are ambiguous because of systematic uncertainties in the ensemble means. Thus we cannot test the two-component spectral hypothesis of Wilkes and Elvis for these objects. SRS X-ray spectra could be steeper than FRS spectra because of the mixing of two components, although a single intrinsically steeper spectrum is easier to reconcile with the absence of z dependence. The uncertainty in a for RQ quasars with high z leaves open the important question of their contribution to the cosmic X-ray background.

Panchromatic study of the first galaxies in cosmological simulations

2019 ◽  
Vol 15 (S341) ◽  
pp. 240-244
Author(s):  
Hidenobu Yajima ◽  
Shohei Arata ◽  
Makito Abe ◽  
Kentaro Nagamine
Keyword(s):  
Star Formation ◽  
Initial Conditions ◽  
High Redshift ◽  
Radiative Properties ◽  
Massive Galaxies ◽  
Star Forming ◽  
Lyman Alpha ◽  
Radiation Properties ◽  
Multi Wavelength ◽  
First Galaxies

AbstractRecent discoveries of high-redshift galaxies have revealed the diversity of their physical properties, from normal star-forming galaxies to starburst galaxies. To understand the properties of these observed galaxies, it is crucial to understand the star formation (SF) history, and the radiation properties associated with the SF activity. Here we present the results of cosmological hydrodynamic simulations with zoom-in initial conditions, and show the formation of the first galaxies and their evolution towards observable galaxies at z = 6. In addition, we show their multi-wavelength radiative properties. We find that star formation occurs intermittently due to supernova (SN) feedback at z > 10, and their radiation properties rapidly change with time. We suggest that the first galaxies are bright at UV wavelengths just after the starburst phase, and become extended Lyman-alpha sources. We also show that massive galaxies cause dusty starburst and become bright at infrared wavelengths.

scholarly journals The importance of magnetic fields for the initial mass function of the first stars

2020 ◽  
Vol 497 (1) ◽  
pp. 336-351 ◽  
Author(s):  
Piyush Sharda ◽  
Christoph Federrath ◽  
Mark R Krumholz
Keyword(s):  
Magnetic Fields ◽  
Initial Conditions ◽  
High Redshift ◽  
Three Dimensional ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Dynamo Theory ◽  
First Stars ◽  
High Redshift Galaxies

ABSTRACT Magnetic fields play an important role for the formation of stars in both local and high-redshift galaxies. Recent studies of dynamo amplification in the first dark matter haloes suggest that significant magnetic fields were likely present during the formation of the first stars in the Universe at redshifts of 15 and above. In this work, we study how these magnetic fields potentially impact the initial mass function (IMF) of the first stars. We perform 200 high-resolution, three-dimensional (3D), magnetohydrodynamic (MHD) simulations of the collapse of primordial clouds with different initial turbulent magnetic field strengths as predicted from turbulent dynamo theory in the early Universe, forming more than 1100 first stars in total. We detect a strong statistical signature of suppressed fragmentation in the presence of strong magnetic fields, leading to a dramatic reduction in the number of first stars with masses low enough that they might be expected to survive to the present-day. Additionally, strong fields shift the transition point where stars go from being mostly single to mostly multiple to higher masses. However, irrespective of the field strength, individual simulations are highly chaotic, show different levels of fragmentation and clustering, and the outcome depends on the exact realization of the turbulence in the primordial clouds. While these are still idealized simulations that do not start from cosmological initial conditions, our work shows that magnetic fields play a key role for the primordial IMF, potentially even more so than for the present-day IMF.

scholarly journals The case for a high-redshift origin of GRB 100205A

2019 ◽  
Vol 488 (1) ◽  
pp. 902-909
Author(s):  
A A Chrimes ◽  
A J Levan ◽  
E R Stanway ◽  
E Berger ◽  
J S Bloom ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Near Infrared ◽  
Gamma Ray ◽  
Hubble Space Telescope ◽  
High Redshift ◽  
Gamma Ray Bursts ◽  
Host Galaxy ◽  
Late Time ◽  
Time Limits

Abstract The number of long gamma-ray bursts (GRBs) known to have occurred in the distant Universe (z &gt; 5) is small (∼15); however, these events provide a powerful way of probing star formation at the onset of galaxy evolution. In this paper, we present the case for GRB 100205A being a largely overlooked high-redshift event. While initially noted as a high-z candidate, this event and its host galaxy have not been explored in detail. By combining optical and near-infrared Gemini afterglow imaging (at t &lt; 1.3 d since burst) with deep late-time limits on host emission from the Hubble Space Telescope, we show that the most likely scenario is that GRB 100205A arose in the range 4 &lt; z &lt; 8. GRB 100205A is an example of a burst whose afterglow, even at ∼1 h post burst, could only be identified by 8-m class IR observations, and suggests that such observations of all optically dark bursts may be necessary to significantly enhance the number of high-redshift GRBs known.

The motion of an ellipsoid in tube flow at low Reynolds numbers

1996 ◽  
Vol 324 ◽  
pp. 287-308 ◽  
Author(s):  
Masako Sugihara-Seki
Keyword(s):  
Initial Conditions ◽  
Flow Direction ◽  
Major Axis ◽  
Oblate Spheroid ◽  
Reynolds Numbers ◽  
Prolate Spheroid ◽  
Stable Configuration ◽  
Axis Ratio ◽  
Low Reynolds Numbers ◽  
Freely Suspended

The motion of a rigid ellipsoidal particle freely suspended in a Poiseuille flow of an incompressible Newtonian fluid through a narrow tube is studied numerically in the zero-Reynolds-number limit. It is assumed that the effect of inertia forces on the motion of the particle and the fluid can be neglected and that no forces or torques act on the particle. The Stokes equation is solved by a finite element method for various positions and orientations of the particle to yield the instantaneous velocity of the particle as well as the flow field around it, and the particle trajectories are determined for different initial configurations. A prolate spheroid is found to either tumble or oscillate in rotation, depending on the particle–tube size ratio, the axis ratio of the particle, and the initial conditions. A large oblate spheroid may approach asymptotically a steady, stable configuration, at which it is located close to the tube centreline, with its major axis slightly tilted from the undisturbed flow direction. The motion of non-axisymmetric ellipsoids is also illustrated and discussed with emphasis on the effect of the particle shape and size.

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