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

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.

scholarly journals Inner and outer rings are not strongly coupled with stellar bars

2019 ◽  
Vol 625 ◽  
pp. A146 ◽  
Author(s):  
S. Díaz-García ◽  
S. Díaz-Suárez ◽  
J. H. Knapen ◽  
H. Salo
Keyword(s):  
Dark Matter ◽  
Numerical Models ◽  
Ring Formation ◽  
Dark Matter Halo ◽  
Strongly Coupled ◽  
Fundamental Parameters ◽  
Barred Galaxies ◽  
Pattern Speed ◽  
Force Calculation ◽  
Disc Galaxies

Rings are distinctive features of many disc galaxies and their location and properties are closely related to the disc dynamics. In particular, rings are often associated to stellar bars, but the details of this connection are far from clear. We have studied the frequency and dimensions of inner and outer rings in the local Universe as a function of disc parameters and the amplitude of non-axisymmetries. We used the 1320 not highly inclined disc galaxies (i <  65°) from the S4G survey. The ring fraction increases with bar Fourier density amplitude: this can be interpreted as evidence for the role of bars in ring formation. The sizes of inner rings are positively correlated with bar strength: this can be linked to the radial displacement of the 1/4 ultraharmonic resonance while the bar grows and the pattern speed decreases. The ring’s intrinsic ellipticity is weakly controlled by the non-axisymmetric perturbation strength: this relation is not as strong as expected from simulations, especially when we include the dark matter halo in the force calculation. The ratio of outer-to-inner ring semi-major axes is uncorrelated with bar strength: this questions the manifold origin of rings. In addition, we confirm that (i) ∼1/3 (∼1/4) of the galaxies hosting inner (outer) rings are not barred; (ii) on average, the sizes and shapes of rings are roughly the same for barred and non-barred galaxies; and (iii) the fraction of inner (outer) rings is a factor of 1.2−1.4 (1.65−1.9) larger in barred galaxies than in their non-barred counterparts. Finally, we apply unsupervised machine learning (self-organising maps, SOMs) to show that, among early-type galaxies, ringed or barred galaxies cannot be univocally distinguished based on 20 internal and external fundamental parameters. We confirm, with the aid of SOMs, that rings are mainly hosted by red, massive, gas-deficient, dark-matter poor, and centrally concentrated galaxies. We conclude that the present-day coupling between rings and bars is not as robust as predicted by numerical models, and diverse physical mechanisms and timescales determine ring formation and evolution.

scholarly journals Models of distorted and evolving dark matter haloes

2020 ◽  
Vol 499 (4) ◽  
pp. 4793-4813
Author(s):  
Jason L Sanders ◽  
Edward J Lilley ◽  
Eugene Vasiliev ◽  
N Wyn Evans ◽  
Denis Erkal
Keyword(s):  
Dark Matter ◽  
Basis Function ◽  
Milky Way ◽  
Dark Matter Halo ◽  
Angular Variation ◽  
Orbital Parameters ◽  
Nearby Galaxies ◽  
Observational Errors ◽  
The Many ◽  
The Impact

ABSTRACT We investigate the ability of basis function expansions to reproduce the evolution of a Milky Way-like dark matter halo, extracted from a cosmological zoom-in simulation. For each snapshot, the density of the halo is reduced to a basis function expansion, with interpolation used to recreate the evolution between snapshots. The angular variation of the halo density is described by spherical harmonics, and the radial variation either by biorthonormal basis functions adapted to handle truncated haloes or by splines. High fidelity orbit reconstructions are attainable using either method with similar computational expense. We quantify how the error in the reconstructed orbits varies with expansion order and snapshot spacing. Despite the many possible biorthonormal expansions, it is hard to beat a conventional Hernquist–Ostriker expansion with a moderate number of terms (≳15 radial and ≳6 angular). As two applications of the developed machinery, we assess the impact of the time-dependence of the potential on (i) the orbits of Milky Way satellites and (ii) planes of satellites as observed in the Milky Way and other nearby galaxies. Time evolution over the last 5 Gyr introduces an uncertainty in the Milky Way satellites’ orbital parameters of $\sim 15 \, \mathrm{per\, cent}$, comparable to that induced by the observational errors or the uncertainty in the present-day Milky Way potential. On average, planes of satellites grow at similar rates in evolving and time-independent potentials. There can be more, or less, growth in the plane’s thickness, if the plane becomes less, or more, aligned with the major or minor axis of the evolving halo.

scholarly journals CONSTRAINTS ON THE SHAPE OF THE MILKY WAY DARK MATTER HALO FROM JEANS EQUATIONS APPLIED TO SLOAN DIGITAL SKY SURVEY DATA

2012 ◽  
Vol 758 (1) ◽  
pp. L23 ◽  
Author(s):  
Sarah R. Loebman ◽  
Željko Ivezić ◽  
Thomas R. Quinn ◽  
Fabio Governato ◽  
Alyson M. Brooks ◽  
...  
Keyword(s):  
Dark Matter ◽  
Survey Data ◽  
Milky Way ◽  
Sloan Digital Sky Survey ◽  
Dark Matter Halo ◽  
Sky Survey

Dark matter bar evolution in triaxial spinning haloes

2020 ◽  
Vol 15 (S359) ◽  
pp. 446-447
Author(s):  
Daniel A. Marostica ◽  
Rubens E. G. Machado
Keyword(s):  
Dark Matter ◽  
The Other ◽  
Barred Galaxies ◽  
Other Hand ◽  
Dynamical Instabilities

AbstractDark matter bars are structures that may form inside dark matter haloes of barred galaxies. Haloes can depart from sphericity and also be subject to some spin. The latter is known to have profound impacts on the evolution of both stellar and DM bars, such as stronger dynamical instabilities, more violent vertical bucklings and dissolution or impairment of stellar bar growth. On the other hand, dark matter bars of spherical haloes become initially stronger in the presence of spin. In this study, we add spin to triaxial halos in order to quantify and compare the strength of their bars. Using N-body simulations, we find that spin accelerates main instabilities and strengthens the halo bars, although their final strength depends only on triaxiality. The most triaxial halo barely forms a halo bar, showing that flattening opposes to DM bar strengthening and indicating that there is a limit on how flattened the parent structure can be.

scholarly journals The constraining effect of gas and the dark matter halo on the vertical stellar distribution of the Milky Way

2018 ◽  
Vol 617 ◽  
pp. A142 ◽  
Author(s):  
S. Sarkar ◽  
C. J. Jog
Keyword(s):  
Dark Matter ◽  
Gravitational Field ◽  
Milky Way ◽  
Galactic Disk ◽  
Outer Region ◽  
Hydrogen Gas ◽  
Dark Matter Halo ◽  
Stellar Disk ◽  
Disk Thickness ◽  
Vertical Density

We study the vertical stellar distribution of the Milky Way thin disk in detail with particular focus on the outer disk. We treat the galactic disk as a gravitationally coupled, three-component system consisting of stars, atomic hydrogen gas, and molecular hydrogen gas in the gravitational field of the dark matter halo. The self-consistent vertical distribution for stars and gas in such a realistic system is obtained for radii between 4–22 kpc. The inclusion of an additional gravitating component constrains the vertical stellar distribution toward the mid-plane, so that the mid-plane density is higher, the disk thickness is reduced, and the vertical density profile is steeper than in the one-component, isothermal, stars-alone case. We show that the stellar distribution is constrained mainly by the gravitational field of gas and dark matter halo in the inner and the outer Galaxy, respectively. We find that the thickness of the stellar disk (measured as the half-width at half-maximum of the vertical density distribution) increases with radius, flaring steeply beyond R = 17 kpc. The disk thickness is reduced by a factor of 3–4 in the outer Galaxy as a result of the gravitational field of the halo, which may help the disk resist distortion at large radii. The disk would flare even more if the effect of dark matter halo were not taken into account. Thus it is crucially important to include the effect of the dark matter halo when determining the vertical structure and dynamics of a galactic disk in the outer region.

scholarly journals Is the dark matter halo of the Milky Way flattened?

2006 ◽  
Vol 461 (1) ◽  
pp. 155-169 ◽  
Author(s):  
A. Růžička ◽  
J. Palouš ◽  
C. Theis
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Dark Matter Halo

scholarly journals The dark matter interpretation of the 3.5-keV line is inconsistent with blank-sky observations

Science ◽  
2020 ◽  
Vol 367 (6485) ◽  
pp. 1465-1467 ◽  
Author(s):  
Christopher Dessert ◽  
Nicholas L. Rodd ◽  
Benjamin R. Safdi
Keyword(s):  
Dark Matter ◽  
Emission Line ◽  
Decay Rate ◽  
Milky Way ◽  
Line Emission ◽  
Mass Range ◽  
Sterile Neutrinos ◽  
X Ray ◽  
Upper Limit ◽  
Nearby Galaxies

Observations of nearby galaxies and galaxy clusters have reported an unexpected x-ray emission line around 3.5 kilo–electron volts (keV). Proposals to explain this line include decaying dark matter—in particular, that the decay of sterile neutrinos with a mass around 7 keV could match the available data. If this interpretation is correct, the 3.5-keV line should also be emitted by dark matter in the halo of the Milky Way. We used more than 30 megaseconds of XMM-Newton (X-ray Multi-Mirror Mission) blank-sky observations to test this hypothesis, finding no evidence of the 3.5-keV line emission from the Milky Way halo. We set an upper limit on the decay rate of dark matter in this mass range, which is inconsistent with the possibility that the 3.5-keV line originates from dark matter decay.

scholarly journals The Dark Matter Content of Barred Spiral Galaxies

2004 ◽  
Vol 220 ◽  
pp. 277-278
Author(s):  
Glen Petitpas ◽  
Mousumi Das ◽  
Peter Teuben ◽  
Stuart Vogel
Keyword(s):  
Dark Matter ◽  
Spiral Galaxies ◽  
Velocity Fields ◽  
Matter Content ◽  
Two Dimensional ◽  
Disk Model ◽  
Barred Galaxies ◽  
Preliminary Results ◽  
Nearby Galaxies ◽  
Barred Spiral Galaxies

Two-dimensional velocity fields have been used to determine the dark matter properties of a sample of barred galaxies taken from the BIMA Survey of Nearby Galaxies (SONG). Preliminary results indicate that the maximal disk model is not appropriate in several galaxies in our sample, but higher resolution results will be needed to confirm this.

scholarly journals Dark matter halo shapes in the Auriga simulations

2019 ◽  
Vol 490 (4) ◽  
pp. 4877-4888 ◽  
Author(s):  
Jesus Prada ◽  
Jaime E Forero-Romero ◽  
Robert J J Grand ◽  
Rüdiger Pakmor ◽  
Volker Springel
Keyword(s):  
Dark Matter ◽  
Strong Influence ◽  
Milky Way ◽  
Spherical Shape ◽  
Dark Matter Halo ◽  
Observational Constraints ◽  
High Degree ◽  
Level Of Agreement

ABSTRACT We present shape measurements of Milky Way–sized dark matter haloes at redshift z = 0 in a suite of 30 zoom simulations from the Auriga project. We compare the results in full magnetohydrodynamics against dark matter–only simulations and find a strong influence of baryons in making dark matter haloes rounder at all radii compared to their dark matter–only counterparts. At distances ≲30 kpc, rounder dark matter distributions correlate with extended massive stellar discs and low-core gas densities. We measure the alignment between the halo and the disc shapes at different radii and find a high degree of alignment at all radii for most of the galaxies. In some cases, the alignment significantly changes as a function of radius implying that the halo shape twists; this effect correlates with recently formed bulges and is almost absent in the dark matter–only simulations. In a comparison against observational constraints, we find that $20{{\ \rm per\ cent}}$ of haloes in our sample are consistent with observational results derived from the Pal 5 stream that favours an almost spherical shape. Including baryons is a required element to achieve this level of agreement. In contrast, none of the simulations (neither dark matter only nor with baryons) match the constraints derived from the Sagittarius stream that favour an oblate dark matter halo.

The 111 and 129 GeVγ-ray lines from annihilations in the Milky Way dark matter halo, dark disk and subhalos

2013 ◽  
Vol 8 (3) ◽  
pp. 4-18
Author(s):  
Ilias Cholis ◽  
Haril Nurbiantoro Santosa ◽  
Maryam Tavakoli ◽  
Piero Ullio
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Dark Matter Halo
Sign in / Sign up

Export Citation Format

Share Document