scholarly journals The Origin and Distribution of Angular Momentum in Galaxies

2004 ◽  
Vol 220 ◽  
pp. 467-476 ◽  
Author(s):  
Joel R. Primack
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Momentum Distribution ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Small Scale ◽  
Dark Halo ◽  
Baryonic Matter ◽  
Dark Matter Halos ◽  
Hydrodynamical Simulations

Cold Dark Matter with a large cosmological constant (ACDM) appears to fit large scale structure observations well. of the possible small scale problems, the Central Cusps and Too Many Satellites problems now appear to be at least partly solved, so Angular Momentum has become the most serious remaining CDM problem. There are actually at least two different angular momentum problems: A. Too much transfer of angular momentum to the dark halo to make big disks, and B. Wrong distribution of specific angular momentum to make spiral galaxies, if the baryonic material has the same angular momentum distribution as the dark matter. the angular momentum of dark matter halos, and presumably that of the galaxies they host, appears to arise largely from the orbital angular momentum of the satellites that they accrete. Since the dark and baryonic matter behave very differently in such accretion events, it is possible that the resulting angular momentum distribution of the baryons is different from that of the dark matter, as required to make the sort of galactic disks that are observed. the latest hydrodynamical simulations give some grounds for hope on this score, but much higher resolution simulations are needed.

scholarly journals The anisotropy of the power spectrum in periodic cosmological simulations

2021 ◽  
Vol 503 (4) ◽  
pp. 5638-5645
Author(s):  
Gábor Rácz ◽  
István Szapudi ◽  
István Csabai ◽  
László Dobos
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Initial Conditions ◽  
Power Spectra ◽  
Cosmological Simulations ◽  
Spherical Collapse ◽  
Lower Amplitude ◽  
Hydrodynamical Simulations

ABSTRACT The classical gravitational force on a torus is anisotropic and always lower than Newton’s 1/r2 law. We demonstrate the effects of periodicity in dark matter only N-body simulations of spherical collapse and standard Lambda cold dark matter (ΛCDM) initial conditions. Periodic boundary conditions cause an overall negative and anisotropic bias in cosmological simulations of cosmic structure formation. The lower amplitude of power spectra of small periodic simulations is a consequence of the missing large-scale modes and the equally important smaller periodic forces. The effect is most significant when the largest mildly non-linear scales are comparable to the linear size of the simulation box, as often is the case for high-resolution hydrodynamical simulations. Spherical collapse morphs into a shape similar to an octahedron. The anisotropic growth distorts the large-scale ΛCDM dark matter structures. We introduce the direction-dependent power spectrum invariant under the octahedral group of the simulation volume and show that the results break spherical symmetry.

scholarly journals Properties of Dark Matter Halos in Disk Galaxies

2004 ◽  
Vol 220 ◽  
pp. 281-286 ◽  
Author(s):  
Roelof S. de Jong ◽  
Susan Kassin ◽  
Eric F. Bell ◽  
Stéphane Courteau
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Momentum Distribution ◽  
Surface Brightness ◽  
High Surface ◽  
Large Set ◽  
Dark Matter Halos ◽  
Rotation Curves ◽  
Galaxy Assembly ◽  
Adiabatic Contraction

We present a simple technique to estimate mass-to-light (M/L) ratios of stellar populations based on two broadband photometry measurements, i.e. a colour-M/L relation. We apply the colour-M/L relation to galaxy rotation curves, using a large set of galaxies that span a great range in Hubble type, luminosity and scale size and that have accurately measured HI and/or Hα rotation curves. Using the colour-M/L relation, we construct stellar mass models of the galaxies and derive the dark matter contribution to the rotation curves.We compare our dark matter rotation curves with adiabatically contracted Navarro, Frenk, & White (1997, NFW hereafter) dark matter halos. We find that before adiabatic contraction most high surface brightness galaxies and some low surface brightness galaxies are well fit by a NFW dark matter profile. However, after adiabatic contraction, most galaxies are poorly fit in the central few kpc. the observed angular momentum distribution in the baryonic component is poorly matched by ACDM model predictions, indicating that the angular momentum distribution is not conserved during the galaxy assembly process. We find that in most galaxies the dark matter distribution can be derived by scaling up the HI gas contribution. However, we find no consistent value for the scaling factor among all the galaxies.

Large-scale structure after COBE: Peculiar velocities and correlations of cold dark matter halos

1994 ◽  
Vol 431 ◽  
pp. 559 ◽  
Author(s):  
Wojciech H. Zurek ◽  
Peter J. Quinn ◽  
John K. Salmon ◽  
Michael S. Warren
Keyword(s):  
Dark Matter ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Dark Matter Halos ◽  
Peculiar Velocities

scholarly journals Voronoi volume function: a new probe of cosmology and galaxy evolution

2020 ◽  
Vol 495 (3) ◽  
pp. 3233-3251 ◽  
Author(s):  
Aseem Paranjape ◽  
Shadab Alam
Keyword(s):  
Dark Matter ◽  
Galaxy Evolution ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Voronoi Tessellation ◽  
Small Scale ◽  
Summary Statistics ◽  
Number Density ◽  
Volume Function ◽  
Space Effects

ABSTRACT We study the Voronoi volume function (VVF) – the distribution of cell volumes (or inverse local number density) in the Voronoi tessellation of any set of cosmological tracers (galaxies/haloes). We show that the shape of the VVF of biased tracers responds sensitively to physical properties such as halo mass, large-scale environment, substructure, and redshift-space effects, making this a hitherto unexplored probe of both primordial cosmology and galaxy evolution. Using convenient summary statistics – the width, median, and a low percentile of the VVF as functions of average tracer number density – we explore these effects for tracer populations in a suite of N-body simulations of a range of dark matter models. Our summary statistics sensitively probe primordial features such as small-scale oscillations in the initial matter power spectrum (as arise in models involving collisional effects in the dark sector), while being largely insensitive to a truncation of initial power (as in warm dark matter models). For vanilla cold dark matter (CDM) cosmologies, the summary statistics display strong evolution and redshift-space effects, and are also sensitive to cosmological parameter values for realistic tracer samples. Comparing the VVF of galaxies in the Galaxies & Mass Assembly (GAMA) survey with that of abundance-matched CDM (sub)haloes tentatively reveals environmental effects in GAMA beyond halo mass (modulo unmodelled satellite properties). Our exploratory analysis thus paves the way for using the VVF as a new probe of galaxy evolution physics as well as the nature of dark matter and dark energy.

scholarly journals Formation of dwarf galaxies and small-scale problems of CDM

2006 ◽  
Vol 2 (S235) ◽  
pp. 385-388
Author(s):  
Oleg Y. Gnedin
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Galactic Halo ◽  
Dwarf Galaxies ◽  
Small Scale ◽  
Dark Matter Halos ◽  
Density Profiles ◽  
Gas Cooling ◽  
Low Efficiency ◽  
The Universe

AbstractThe concordance cosmological model based on cold dark matter makes definitive predictions for the growth of galaxies in the Universe, which are being actively studied using numerical simulations. These predictions appear to contradict the observations of dwarf galaxies. Dwarf dark matter halos are more numerous and have steeper central density profiles than the observed galaxies. The first of these small-scale problems, the “missing satellites problem”, can be resolved by accounting for the low efficiency of gas cooling and star formation in dwarf halos. A newly-discovered class of HyperVelocity Stars will soon allow us to test another generic prediction of CDM models, the triaxial shapes of dark matter halos. Measuring the proper motions of HVS will probe the gravitational potential out to 100 kpc and will constrain the axis ratios and the orientation of the Galactic halo.

scholarly journals Cold Dark Matter: Galactic Halos

1987 ◽  
Vol 117 ◽  
pp. 280-280
Author(s):  
C. S. Frenk
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Galaxy Formation ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Initial Conditions ◽  
Standard Theory ◽  
Galactic Halos ◽  
Rotation Curves ◽  
Central Regions

A flat universe dominated by cold dark matter (CDM) is an attractive arena for the formation of galaxies and large scale structure. Current upper limits on anisotropies of the cosmic microwave background and the standard theory of primordial nucleosynthesis are both compatible with such a universe. Furthermore a flat CDM model in which galaxy formation is biased towards high density regions provides a good match to the observed distribution of galaxies on Megaparsec scales. In collaboration with M. Davis, G. Efstathiou and S.D.M. White, we have carried out a high resolution N-body simulation which shows that this model can also account for the abundance and characteristic properties of galactic halos. The initial conditions for this simulation were based on the results of our previous work which gave both the scaling and overall normalisation of the initial CDM fluctuation spectrum appropriate to the biased galaxy formation model. We simulated a cubic region of present size 14 Mpc (H0 = 50km/s/Mpc) from a redshift of 6 to the present day, with a resolution of 2kpc initially and 14 kpc at the end. We found that by a redshift of 2.5 about 20 clumps with circular speeds exceeding 100 km/s had collapsed near high peaks of the initial linear density field. Between Z = 2.5 and the present most of them remained isolated and accreted extensive outer halos, while others merged into larger systems. The rotation curves of the final smooth systems were impressively flat at large radii resembling the measured rotation curves of spiral galaxies. Furthermore, the abundance of clumps with circular velocities larger than 150 km/s was about the same as the abundance of galaxies brighter than M33 expected in a volume the size of our simulation. Significant transfer of angular momentum to surrounding material occurred as large subclumps merged. Most of this angular momentum was originally invested in the orbital motions of the subclumps. As a result, the central regions of merged objects showed little rotation.

The shapes of simulated dark matter halos

2004 ◽  
Vol 220 ◽  
pp. 421-429 ◽  
Author(s):  
Volker Springel ◽  
Simon D. M. White ◽  
Lars Hernquist
Keyword(s):  
Dark Matter ◽  
Major Axis ◽  
Elliptical Galaxies ◽  
Radiative Cooling ◽  
Dark Halo ◽  
Dark Matter Halos ◽  
Robust Method ◽  
Shape Distribution ◽  
Measurement Uncertainties ◽  
Hydrodynamical Simulations

Dark matter halos formed in CDM simulations are known to have triaxial shapes, with substantial distortions from spherical symmetry. However, conflicting claims have been made with respect to radial variations of halo shape, or trends with mass. We propose a new, more robust method to determine halo shapes based on the gravitational potential, thereby avoiding measurement uncertainties that may be the cause of these discrepancies. We find a strong preference towards prolate halo shapes, with mean minor-to-major axis-ratios close to ~ 0.5. Spherical halos are generally very rare, but there is a trend for smaller mass systems to be less elongated. We also compare dark halo shapes found in hydrodynamical simulations that include radiative cooling, star formation, and feedback processes, with those measured in equivalent collisionless simulations. Dissipation makes dark halos substantially rounder at small radii, to the extent that their shape distribution matches that of elliptical galaxies.

scholarly journals Globular Clusters and Streaming Velocities: Testing the New Formation Channel in High-resolution Cosmological Simulations

2021 ◽  
Vol 922 (2) ◽  
pp. 193
Author(s):  
Anna T. P. Schauer ◽  
Volker Bromm ◽  
Michael Boylan-Kolchin ◽  
Simon C. O. Glover ◽  
Ralf S. Klessen
Keyword(s):  
Dark Matter ◽  
Early Universe ◽  
Globular Clusters ◽  
Large Scale ◽  
Compact Star ◽  
Star Clusters ◽  
Dark Matter Halos ◽  
Metal Enrichment ◽  
Hydrodynamical Simulations ◽  
Population Iii

Abstract The formation of globular clusters and their relation to the distribution of dark matter have long puzzled astronomers. One of the most recently proposed globular cluster formation channels ties ancient star clusters to the large-scale streaming velocity of baryons relative to dark matter in the early universe. These streaming velocities affect the global infall of baryons into dark matter halos, the high-redshift halo mass function, and the earliest generations of stars. In some cases, streaming velocities may result in dense regions of dark matter-free gas that becomes Jeans unstable, potentially leading to the formation of compact star clusters. We investigate this hypothesis using cosmological hydrodynamical simulations that include a full chemical network and the formation and destruction of H2, a process crucial for the formation of the first stars. We find that high-density gas in regions with significant streaming velocities is indeed somewhat offset from the centers of dark matter halos, but this offset is typically significantly smaller than the virial radius. Gas outside of dark matter halos never reaches Jeans-unstable densities in our simulations. We postulate that low-level (Z ≈ 10−3 Z ⊙) metal enrichment by Population III supernovae may enable cooling in the extra-virial regions, allowing gas outside of dark matter halos to cool to the cosmic microwave background temperature and become Jeans unstable. Follow-up simulations that include both streaming velocities and metal enrichment by Population III supernovae are needed to understand if streaming velocities provide one path for the formation of globular clusters in the early universe.

scholarly journals How galaxies gain and lose their angular momentum

2007 ◽  
Vol 3 (S245) ◽  
pp. 51-54
Author(s):  
Elena D'Onghia
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Minor Role ◽  
Dark Matter Halos ◽  
Tidal Interactions ◽  
Higher Spin ◽  
Tidal Torques ◽  
A Minor

AbstractSpiral, fast-rotating galaxies like the Milky Way are the most common type in the Universe. One of the most pressing challenges faced by current models of galaxy formation is the origin of their angular momentum and disk. According to the standard tidal-torque theory the galactic spin is originated by tidal interactions between dark halos around galaxies and neighboring structures in the expanding Universe. We use a large cosmological N-body simulation to study the origin of possible correlations between the merging history and spin of cold dark matter halos. In particular, we examine claims that remnants of major mergers tend to have higher-than-average spins, and find that the effect is driven largely by unrelaxed systems: equilibrium dark matter halos show no significant correlation between spin and merging history. Out-of-equilibrium halos have, on average, higher spin than relaxed systems, suggesting that the virialization process leads to a net decrease in the value of the spin parameter. We present also high-resolution N-body/SPH cosmological simulations including cold gas and dark matter to investigate the processes by which gas loses its angular momentum during the protogalactic collapse phase, leading to simulated disk galaxies that are too compact with respect to the observations. We show that the gas and the dark matter have similar specific angular momenta until a merger event occurs at redshift 2. All the gas involved in the merger loses a substantial fraction of its specific angular momentum due to tidal torques and falls quickly into the center. Dynamical friction by small infalling substructures plays a minor role, in contrast to previous claims.

scholarly journals Collapse of spherical overdensities in superfluid models of dark matter

2020 ◽  
Vol 639 ◽  
pp. A90
Author(s):  
S. T. H. Hartman ◽  
H. A. Winther ◽  
D. F. Mota
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Small Scale ◽  
Linear Perturbation ◽  
Dark Matter Halos ◽  
Thermal Pressure ◽  
Normal Fluid ◽  
Superfluid Fraction ◽  
Scale Structures ◽  
Small Scale Structures

Aims. We intend to understand cosmological structure formation within the framework of superfluid models of dark matter with finite temperatures. Of particular interest is the evolution of small-scale structures where the pressure and superfluid properties of the dark matter fluid are prominent. We compare the growth of structures in these models with the standard cold dark matter paradigm and non-superfluid dark matter. Methods. The equations for superfluid hydrodynamics were computed numerically in an expanding ΛCDM background with spherical symmetry; the effect of various superfluid fractions, temperatures, interactions, and masses on the collapse of structures was taken into consideration. We derived the linear perturbation of the superfluid equations, giving further insights into the dynamics of the superfluid collapse. Results. We found that while a conventional dark matter fluid with self-interactions and finite temperatures experiences a suppression in the growth of structures on smaller scales, as expected due to the presence of pressure terms, a superfluid can collapse much more efficiently than was naively expected due to its ability to suppress the growth of entropy perturbations and thus gradients in the thermal pressure. We also found that the cores of the dark matter halos initially become more superfluid during the collapse, but eventually reach a point where the superfluid fraction falls sharply. The formation of superfluid dark matter halos surrounded by a normal fluid dark matter background is therefore disfavored by the present work.

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