Bars in Cuspy Dark Halos

AbstractWe examine the bar instability in models with an exponential disk and a cuspy NFW-like dark matter (DM) halo inspired by cosmological simulations. Bar evolution is studied as a function of numerical resolution in a sequence of models spanning 104 – 108 DM particles - including a multi-mass model with an effective resolution of 1010. The goal is to find convergence in dynamical behaviour. We characterize the bar growth, the buckling instability, pattern speed decay through resonant transfer of angular momentum, and possible destruction of the DM halo cusp. Overall, most characteristics converge in behaviour for halos containing more than 107 particles in detail. Notably, the formation of the bar does not destroy the density cusp in this case. These higher resolution simulations clearly illustrate the importance of discrete resonances in transporting angular momentum from the bar to the halo.

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Evolution of Spiral Galaxies in Modified Gravity

Proceedings of the International Astronomical Union ◽

10.1017/s174392130600576x ◽

2006 ◽

Vol 2 (S235) ◽

pp. 144-144

Author(s):

O. Tiret ◽

F. Combes

Keyword(s):

Differential Equation ◽

Modified Gravity ◽

Spiral Galaxies ◽

Nonlinear Partial Differential Equation ◽

Dynamical Behaviour ◽

Second Phase ◽

Stellar Disc ◽

Numerical Resolution ◽

Hubble Sequence ◽

Pattern Speed

We present N-body simulations performed in the framework of MOND. This work is based on a numerical resolution of the modified Poisson equation derived from a Lagrangian theory of MOND. This equation is a nonlinear partial differential equation, so we first developed a code that solves this kind of equations using multigrid techniques. We compared the dynamical behaviour of a typical isolated galaxy in Newton CDM model and MOND model. In this approach, pure stellar disc are considered. For the same value of the Toomre parameter (QT), galactic discs in MOND develop a bar instability sooner than in the DM model. In a second phase the MOND bars weaken while the DM bars continue to grow by exchanging angular momentum with the halo. The bar pattern speed evolves quite differently in the two models, this affects the position of resonance like the corotation and the peanut. Then we studied the evolution of several galactic discs representing the Hubble sequence, in both models. These simulations lead to a statistical bar frequency which is closer to observations for the MOND than the DM model.

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The kinematics and dark matter fractions of TNG50 galaxies at z = 2 from an observational perspective

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3464 ◽

2020 ◽

Vol 500 (4) ◽

pp. 4597-4619

Author(s):

Hannah Übler ◽

Shy Genel ◽

Amiel Sternberg ◽

Reinhard Genzel ◽

Sedona H Price ◽

...

Keyword(s):

Dark Matter ◽

Adaptive Optics ◽

Near Infrared ◽

Matter Content ◽

Cosmological Simulations ◽

Star Forming ◽

Numerical Resolution ◽

Gas Kinematics ◽

Sufficient Detail ◽

Disc Rotation

ABSTRACT We contrast the gas kinematics and dark matter contents of z = 2 star-forming galaxies (SFGs) from state-of-the-art cosmological simulations within the ΛCDM framework to observations. To this end, we create realistic mock observations of massive SFGs ($M_*\gt 4\times 10^{10} \, \mathrm{M}_{\odot}$, SFR >50 M⊙ yr−1) from the TNG50 simulation of the IllustrisTNG suite, resembling near-infrared, adaptive-optics assisted integral-field observations from the ground. Using observational line fitting and modelling techniques, we analyse in detail the kinematics of seven TNG50 galaxies from five different projections per galaxy, and compare them to observations of twelve massive SFGs by Genzel et al. (2020). The simulated galaxies show clear signs of disc rotation but mostly exhibit more asymmetric rotation curves, partly due to large intrinsic radial and vertical velocity components. At identical inclination angle, their 1D velocity profiles can vary along different lines of sight by up to Δv = 200 km s−1. From dynamical modelling we infer rotation speeds and velocity dispersions that are broadly consistent with observational results. We find low central dark matter fractions compatible with observations ($f_{\rm DM}^v(\lt R_e)=v_{\rm DM}^2(R_e)/v_{\rm circ}^2(R_e)\sim 0.32\pm 0.10$), however for disc effective radii Re that are mostly too small: at fixed Re the TNG50 dark matter fractions are too high by a factor of ∼2. We speculate that the differences in gas kinematics and dark matter content compared to the observations may be due to physical processes that are not resolved in sufficient detail with the numerical resolution available in current cosmological simulations.

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Bars and the connection between dark and visible matter

Symposium - International Astronomical Union ◽

10.1017/s0074180900183330 ◽

2004 ◽

Vol 220 ◽

pp. 255-264 ◽

Cited By ~ 6

Author(s):

E. Athanassoula

Keyword(s):

Dark Matter ◽

Angular Momentum ◽

Barred Galaxies ◽

Visible Matter ◽

Pattern Speed ◽

Disc Galaxies

Isolated barred galaxies evolve by redistributing their internal angular momentum, which is emitted mainly at the inner disc resonances and absorbed mainly at the resonances in the outer disc and the halo. This causes the bar to grow stronger and its pattern speed to decrease with time. A massive, responsive halo enhances this process. I show correlations and trends between the angular momentum absorbed by the halo and the bar strength, pattern speed and morphology. It is thus possible to explain why some disc galaxies are strongly barred, while others have no bar, or only a short bar or an oval. in some cases, a bar is found also in the halo component. This “halo bar” is triaxial, but more prolate-like, is shorter than the disc bar and rotates with roughly the same pattern speed. I finally discuss whether bars can modify the density cusps found in cosmological CDM simulations of dark matter haloes.

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The anisotropy of the power spectrum in periodic cosmological simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab874 ◽

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.

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Dark matter candidates in a type-II radiative neutrino mass model

Journal of High Energy Physics ◽

10.1007/jhep06(2021)072 ◽

2021 ◽

Vol 2021 (6) ◽

Author(s):

Roberto A. Lineros ◽

Mathias Pierre

Keyword(s):

Dark Matter ◽

Neutral Particle ◽

Matter Density ◽

Indirect Detection ◽

Dark Matter Candidate ◽

Neutrino Masses ◽

Type Ii ◽

Mass Model ◽

Direct And Indirect Detection

Abstract We explore the connection between Dark Matter and neutrinos in a model inspired by radiative Type-II seessaw and scotogenic scenarios. In our model, we introduce new electroweakly charged states (scalars and a vector-like fermion) and impose a discrete ℤ2 symmetry. Neutrino masses are generated at the loop level and the lightest ℤ2-odd neutral particle is stable and it can play the role of a Dark Matter candidate. We perform a numerical analysis of the model showing that neutrino masses and flavour structure can be reproduced in addition to the correct dark matter density, with viable DM masses from 700 GeV to 30 TeV. We explore direct and indirect detection signatures and show interesting detection prospects by CTA, Darwin and KM3Net and highlight the complementarity between these observables.

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Dark matter annihilation feedback in cosmological simulations – II. The influence on gas and halo structure

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz435 ◽

2019 ◽

Vol 485 (1) ◽

pp. 1420-1434 ◽

Cited By ~ 3

Author(s):

N Iwanus ◽

P J Elahi ◽

F List ◽

G F Lewis

Keyword(s):

Dark Matter ◽

Dark Matter Annihilation ◽

Cosmological Simulations ◽

Halo Structure

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Double X/Peanut Structures in Barred Galaxies – Insights from an N–body Simulation

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3814 ◽

2020 ◽

Author(s):

Bogdan C Ciambur ◽

Francesca Fragkoudi ◽

Sergey Khoperskov ◽

Paola Di Matteo ◽

Françoise Combes

Keyword(s):

Dark Matter ◽

Milky Way ◽

Large Fraction ◽

Formation Time ◽

Dark Matter Halo ◽

Barred Galaxies ◽

Pattern Speed ◽

Nearby Galaxies ◽

Dynamical Instabilities ◽

Bow Tie

Abstract Boxy, peanut– or X–shaped “bulges” are observed in a large fraction of barred galaxies viewed in, or close to, edge-on projection, as well as in the Milky Way. They are the product of dynamical instabilities occurring in stellar bars, which cause the latter to buckle and thicken vertically. Recent studies have found nearby galaxies that harbour two such features arising at different radial scales, in a nested configuration. In this paper we explore the formation of such double peanuts, using a collisionless N–body simulation of a pure disc evolving in isolation within a live dark matter halo, which we analyse in a completely analogous way to observations of real galaxies. In the simulation we find a stable double configuration consisting of two X/peanut structures associated to the same galactic bar – rotating with the same pattern speed – but with different morphology, formation time, and evolution. The inner, conventional peanut-shaped structure forms early via the buckling of the bar, and experiences little evolution once it stabilises. This feature is consistent in terms of size, strength and morphology, with peanut structures observed in nearby galaxies. The outer structure, however, displays a strong X, or “bow-tie”, morphology. It forms just after the inner peanut, and gradually extends in time (within 1 to 1.5 Gyr) to almost the end of the bar, a radial scale where ansae occur. We conclude that, although both structures form, and are dynamically coupled to, the same bar, they are supported by inherently different mechanisms.

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Rotation of Galaxy Dark Matter Halos

Proceedings of the International Astronomical Union ◽

10.1017/s1743921306005394 ◽

2006 ◽

Vol 2 (S235) ◽

pp. 104-104

Author(s):

Stéphane Herbert-Fort ◽

Dennis Zaritsky ◽

Yeun Jin Kim ◽

Jeremy Bailin ◽

James E. Taylor

Keyword(s):

Dark Matter ◽

Angular Momentum ◽

Numerical Simulations ◽

Galaxy Formation ◽

Spiral Galaxy ◽

Observational Studies ◽

Spiral Galaxies ◽

Satellite System ◽

Dark Matter Halos ◽

The Mean

AbstractThe degree to which outer dark matter halos of spiral galaxies rotate with the disk is sensitive to their accretion history and may be probed with associated satellite galaxies. We use the Steward Observatory Bok telescope to measure the sense of rotation of nearby isolated spirals and combine these data with those of their associated satellites (drawn from SDSS) to directly test predictions from numerical simulations. We aim to constrain models of galaxy formation by measuring the projected component of the halo angular momentum that is aligned with that of spiral galaxy disks, Jz. We find the mean bulk rotation of the ensemble satellite system to be co-rotating with the disk with a velocity of 22 ± 13 km/s, in general agreement with previous observational studies and suggesting that galaxy disks could be formed by halo baryons collapsing by a factor of ≈10. We also find a prograde satellite fraction of 51% and Jz, of the satellite system to be positively correlated with the disk, albeit at low significance (2655 ± 2232 kpc km/s).

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