Analysis methods for Milky Way dark matter halo detection

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833510 ◽

2018 ◽

Vol 617 ◽

pp. A142 ◽

Cited By ~ 5

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.

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Is the dark matter halo of the Milky Way flattened?

Astronomy and Astrophysics ◽

10.1051/0004-6361:20065538 ◽

2006 ◽

Vol 461 (1) ◽

pp. 155-169 ◽

Cited By ~ 20

Author(s):

A. Růžička ◽

J. Palouš ◽

C. Theis

Keyword(s):

Dark Matter ◽

Milky Way ◽

Dark Matter Halo

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Dark matter halo shapes in the Auriga simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2873 ◽

2019 ◽

Vol 490 (4) ◽

pp. 4877-4888 ◽

Cited By ~ 4

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.

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

Astronomical Review ◽

10.1080/21672857.2013.11519721 ◽

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

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Cold Dark Matter Substructure and the Heating of Galactic Disks

Symposium - International Astronomical Union ◽

10.1017/s0074180900207419 ◽

2003 ◽

Vol 208 ◽

pp. 391-392

Author(s):

Andreea S. Font ◽

Julio F. Navarro

Keyword(s):

Dark Matter ◽

Cold Dark Matter ◽

Milky Way ◽

Dark Matter Halo ◽

Stellar Disk ◽

Minor Role ◽

Galactic Disks ◽

Cosmological Simulations ◽

A Minor

We investigate recent suggestions that substructure in cold dark matter (CDM) halos has potentially destructive effects on galactic disks. N-body simulations of disk/bulge models of the Milky Way, embedded in a dark matter halo with substructure similar to that found in cosmological simulations, show that tides from substructure halos play only a minor role in the dynamical heating of the stellar disk. This suggests that substructure might not preclude CDM halos from being acceptable hosts of thin stellar disks.

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On the Shape of the Galactic Dark Matter Halo

Publications of the Astronomical Society of Australia ◽

10.1071/as04032 ◽

2004 ◽

Vol 21 (2) ◽

pp. 212-215 ◽

Cited By ~ 4

Author(s):

Amina Helmi

Keyword(s):

Dark Matter ◽

Numerical Simulations ◽

Cold Dark Matter ◽

Milky Way ◽

Dark Matter Halo ◽

Dark Halo ◽

Galactic Dark Matter ◽

Galactic Potentials ◽

Strong Contrast

AbstractThe confined nature of the debris from the Sagittarius dwarf to a narrow trail on the sky has recently prompted the suggestion that the dark matter halo of our Galaxy should be nearly spherical (Ibata et al. 2001; Majewski et al. 2003). This would seem to be in strong contrast with predictions from cold dark matter (CDM) simulations, where dark halos are found to have typical density axis ratios of 0.6 to 0.8. Here I present numerical simulations of the evolution of a system like the Sagittarius dSph in a set of Galactic potentials with varying degrees of flattening. These simulations show that the Sagittarius streams discovered so far are too young dynamically to be sensitive to the shape of the dark halo of the Milky Way. The data presently available are entirely consistent with a Galactic dark matter halo that could either be oblate or prolate, with density axis ratios c/a that range from 0.6 to 1.6 within the region of the halo probed by the orbit of the Sagittarius dwarf.

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A dark matter profile to model diverse feedback-induced core sizes of ΛCDM haloes

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2101 ◽

2020 ◽

Vol 497 (2) ◽

pp. 2393-2417 ◽

Cited By ~ 5

Author(s):

Alexandres Lazar ◽

James S Bullock ◽

Michael Boylan-Kolchin ◽

T K Chan ◽

Philip F Hopkins ◽

...

Keyword(s):

Dark Matter ◽

Galaxy Formation ◽

Cold Dark Matter ◽

Milky Way ◽

Dark Matter Halo ◽

Constant Density ◽

Core Formation ◽

Density Profiles ◽

The Galaxy ◽

Two Parameter

ABSTRACT We analyse the cold dark matter density profiles of 54 galaxy haloes simulated with Feedback In Realistic Environments (FIRE)-2 galaxy formation physics, each resolved within $0.5{{\ \rm per\ cent}}$ of the halo virial radius. These haloes contain galaxies with masses that range from ultrafaint dwarfs ($M_\star \simeq 10^{4.5}\, \mathrm{M}_{\odot }$) to the largest spirals ($M_\star \simeq 10^{11}\, \mathrm{M}_{\odot }$) and have density profiles that are both cored and cuspy. We characterize our results using a new, analytic density profile that extends the standard two-parameter Einasto form to allow for a pronounced constant density core in the resolved innermost radius. With one additional core-radius parameter, rc, this three-parameter core-Einasto profile is able to characterize our feedback-impacted dark matter haloes more accurately than other three-parameter profiles proposed in the literature. To enable comparisons with observations, we provide fitting functions for rc and other profile parameters as a function of both M⋆ and M⋆/Mhalo. In agreement with past studies, we find that dark matter core formation is most efficient at the characteristic stellar-to-halo mass ratio M⋆/Mhalo ≃ 5 × 10−3, or $M_{\star } \sim 10^9 \, \mathrm{M}_{\odot }$, with cores that are roughly the size of the galaxy half-light radius, rc ≃ 1−5 kpc. Furthermore, we find no evidence for core formation at radii $\gtrsim 100\ \rm pc$ in galaxies with M⋆/Mhalo < 5 × 10−4 or $M_\star \lesssim 10^6 \, \mathrm{M}_{\odot }$. For Milky Way-size galaxies, baryonic contraction often makes haloes significantly more concentrated and dense at the stellar half-light radius than DMO runs. However, even at the Milky Way scale, FIRE-2 galaxy formation still produces small dark matter cores of ≃ 0.5−2 kpc in size. Recent evidence for a ∼2 kpc core in the Milky Way’s dark matter halo is consistent with this expectation.

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The effect of warm gas on the buckling instability in galactic bars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937165 ◽

2020 ◽

Vol 634 ◽

pp. A122

Author(s):

Ewa L. Łokas

Keyword(s):

Dark Matter ◽

Milky Way ◽

Gas Content ◽

Dark Matter Halo ◽

Buckling Instability ◽

Radial Profiles ◽

Formation And Evolution ◽

The One ◽

Gas Fractions ◽

Gas Component

By using N-body and hydro simulations, we study the formation and evolution of bars in galaxies with significant gas content focusing on the phenomenon of the buckling instability. The galaxies are initially composed of a spherical dark matter halo and only stellar, or stellar and gaseous, disks with parameters that are similar to the Milky Way and are evolved for 10 Gyr. We consider different values of the gas fraction f = 0−0.3 and in order to isolate the effect of the gas, we kept the fraction constant during the evolution by not allowing the gas to cool and form stars. The stellar bars that form in simulations with higher gas fractions are weaker and shorter, and they do not form at all for gas fractions that are higher than 0.3. The bar with a gas fraction of 0.1 forms sooner due to initial perturbations in the gas, but despite the longer evolution, it does not become stronger than the one in the collisionless case at the end of evolution. The bars in the gas component are weaker; they reach their maximum strength around 4 Gyr and later decline to transform into spheroidal shapes. The distortion of the stellar bar during the buckling instability is weaker for higher gas fractions and weakens the bar less significantly, but it has a similar structure both in terms of radial profiles and in face-on projections. For f = 0.2, the first buckling lasts significantly longer and the bar does not undergo the secondary buckling event, while for f = 0.3, the buckling does not occur. Despite these differences, all bars develop boxy/peanut shapes in the stellar and gas component by the end of the evolution, although their thickness is smaller for higher gas fractions.

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