The twisted dark matter halo of the Milky Way

Shao, Shi; Cautun, Marius; Deason, Alis J.; Frenk, Carlos S.

doi:10.1093/mnras/staa3883

Cited by 22 publications

(25 citation statements)

References 115 publications

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“…In G23 there is also close alignment between the disc axis and the DM minor axis within 100 kpc after the flip, although this alignment is weaker in G19 and G27. This is consistent with the inferences of Shao et al (2020) that the minor axis of the Milky Way's inner DM halo is perpendicular to its disc. Other work on simulations (e.g., Hahn et al 2010) also shows that the minor axes of inner DM haloes tend to be well-aligned with stellar and gas discs (see also Debattista et al 2008Debattista et al , 2015.…”

Section: Disc Flippingsupporting

confidence: 92%

“…Using the method described in Section 4.1, we found the principal axes of the DM halo. In the Milky Way there is reason to believe that the DM halo minor axis direction changes between inner and outer radii (e.g., see Shao et al 2020;Deason et al 2011). Motivated by this, as in Section 4.1 we calculated the tensor 𝐼 𝑗 𝑘 twice, for DM particles within 𝑟 = 30 kpc and 𝑟 = 100 kpc.…”

Section: Disc Flippingmentioning

confidence: 99%

“…Note, however, that satellites also prefer to be co-planar with the host's stellar disc, making the MW's arrangement rather remarkable and rare. A picture therefore emerges in which the main direction of the Galactic DM accretion underwent a dramatic swerve in the last 8-10 Gyr instigated by a change in the surrounding large-scale structure (see Shao et al 2021). The GS accretion is probably the only major event in our Galaxy's past that occurred at approximately the same time.…”

Section: Introductionmentioning

confidence: 97%

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Merger-induced galaxy transformations in the ARTEMIS simulations

Dillamore,

Belokurov,

Font

et al. 2021

Preprint

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Using the ARTEMIS set of 45 high-resolution cosmological simulations, we investigate a range of merger-induced dynamical transformations of Milky Way-like galaxies. We first identify populations of accreted stars on highly radial orbits, similar to the 'Gaia Sausage' in the Milky Way. We show that ≈ 1/3 of the ARTEMIS galaxies contain a similar feature, and confirm that they usually comprise stellar debris from the most massive accreted satellite. Selecting these 15 galaxies, we study their changes around the times of the GS-like mergers. Dark matter haloes of many of these exhibit global changes in shape and orientation. Focusing on the galaxies themselves, we find multiple examples of stellar discs whose angular momentum (AM) axes change orientation at rapid rates of ∼ 60 degrees Gyr −1 . By calculating the orbital angular momentum axes of the satellites before they are accreted, we show that there is a tendency for the disc's AM to become more aligned with this axis after the merger. We also investigate the origin of in situ retrograde stars, analogous to the 'Splash' in the Milky Way. Tracing them back to earlier snapshots, we demonstrate that they were often disrupted onto their extreme orbits by multiple early mergers. We also find that the total mass of these stars outside the central regions positively correlates with the total accreted stellar mass. Finally, we conduct a brief investigation into whether bars form soon after the mergers. In a few galaxies we find a bar-like feature whose emergence coincides with a significant merger.

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Section: Disc Flippingsupporting

confidence: 92%

Section: Disc Flippingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

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Merger-induced galaxy transformations in the ARTEMIS simulations

Dillamore,

Belokurov,

Font

et al. 2021

Preprint

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“…In spite of that, later models, like those of Gibbons et al (2014), Dierickx & Loeb (2017) or Fardal et al (2019), use mostly spherical models with different radial profiles. Recently, though, Vasiliev et al (2021, hereafter V21) proposed instead a twisted halo that transitions from prolate in the outer parts to oblate in the inner parts (see Shao et al 2021, although they find it oblate in the outer parts) which, once combined with the effect of the infalling massive Large Magellanic Cloud (LMC), produces an excellent agreement with the Gaia second data release (DR2). It is important to point out, however, that all these models are based mostly on fits to the younger part of the stream (dominated by the material stripped at the penultimate pericentre), which has less constraining power than the material stripped at the antepenultimate pericentre (i.e., 2Gyr ago), and completely neglect the presence of the bifurcations whose origins remain a mystery.…”

Section: Introductionmentioning

confidence: 93%

The Sagittarius stream in Gaia eDR3 and the origin of the bifurcations

Ramos,

Antoja,

Yuan

et al. 2021

Preprint

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Context. The Sagittarius dwarf spheroidal (Sgr) is a dissolving galaxy being tidally disrupted by the Milky Way (MW). Its stellar stream still poses serious modelling challenges, which hinders our ability to use it effectively as a prospective probe of the MW gravitational potential at large radii. Aims. Our goal is to construct the largest and most stringent sample of stars in the stream with which we can advance our understanding of the Sgr-MW interaction, focusing on the characterisation of the bifurcations. Methods. We improve on previous methods based on the use of the wavelet transform to systematically search for the kinematic signature of the Sgr stream throughout the whole sky in the Gaia data. We then refine our selection via the use of a clustering algorithm on the statistical properties of the colour-magnitude diagrams. Results. Our final sample contains more than 700k candidate stars, 3x larger than previous Gaia samples. With it, we have been able to detect the bifurcation of the stream in both the northern and southern hemispheres, requiring four branches (two bright and two faint) to fully describe this system. We present the detailed proper motion distribution of the trailing arm as a function of the angular coordinate along the stream showing, for the first time, the presence of a sharp edge (on the side of the small proper motions) beyond which there are no Sgr stars. We also characterise the correlation between kinematics and distance. Finally, the chemical analysis of our sample shows a significant difference between the faint and bright branches of the bifurcation. We provide analytical descriptions for the proper motion trends as well as for the sky distribution of the four branches of the stream. Conclusions. Based on our analysis, we interpret the bifurcations as the misaligned overlap of the material stripped at the antepenultimate pericentre (faint branches) with the stars ejected at the penultimate pericentre (bright branch), given that Sgr just went through its perigalacticon. The source of this misalignment is still unknown but we argue that models with some internal rotation in the progenitor -at least during the time of stripping of the stars that are now in the faint branches -are worth exploring.

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“…Bailin & Steinmetz 2005;Shao et al 2016). In particular, based on hydrodynamical simulations the inner halo is expected to be aligned with the Galactic disc, while the orbit of the Sagittarius stream, as well as the disc of satellite galaxies, indicate that the outer halo is perpendicular to the MW disc (Law & Majewski 2010;Vera-Ciro & Helmi 2013;Shao et al 2019a), with the transition between the two halo orientations occurring at an as yet unconstrained distance.…”

Section: Limitations and Future Improvementsmentioning

confidence: 99%

The milky way total mass profile as inferred from Gaia DR2

Cautun

Benítez-Llambay

Deason

et al. 2020

Monthly Notices of the Royal Astronomical Society

Self Cite

301

271

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We determine the Milky Way (MW) mass profile inferred from fitting physically motivated models to the Gaia DR2 Galactic rotation curve and other data. Using various hydrodynamical simulations of MW-mass haloes, we show that the presence of baryons induces a contraction of the dark matter (DM) distribution in the inner regions, r 20 kpc. We provide an analytic expression that relates the baryonic distribution to the change in the DM halo profile. For our galaxy, the contraction increases the enclosed DM halo mass by factors of roughly 1.3, 2 and 4 at radial distances of 20, 8 and 1 kpc, respectively compared to an uncontracted halo. Ignoring this contraction results in systematic biases in the inferred halo mass and concentration. We provide a best-fitting contracted NFW halo model to the MW rotation curve that matches the data very well. The best-fit has a DM halo mass, M DM 200 = 0.99 +0.18 −0.20 ×10 12 M , and concentration before baryon contraction of 8.2 +1.7 −1.5 , which lie close to the median halo mass-concentration relation predicted in ΛCDM. The inferred total mass, M total 200 = 1.12 +0.20 −0.22 × 10 12 M , is in good agreement with recent measurements. The model gives a MW stellar mass of 4.99 +0.34 −0.50 × 10 10 M , of which 60% is contained in the thin stellar disc, with a bulge-to-total ratio of 0.2. We infer that the DM density at the Solar position is ρ DM = 9.0 +0.5 −0.4 × 10 −3 M pc −3 ≡ 0.34 +0.02 −0.02 GeV cm −3 . The rotation curve data can also be fitted with an uncontracted NFW halo model, but with very different DM and stellar parameters. The observations prefer the physically motivated contracted NFW halo, but the measurement uncertainties are too large to rule out the uncontracted NFW halo.

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The twisted dark matter halo of the Milky Way

Cited by 22 publications

References 115 publications

Merger-induced galaxy transformations in the ARTEMIS simulations

Merger-induced galaxy transformations in the ARTEMIS simulations

The Sagittarius stream in Gaia eDR3 and the origin of the bifurcations

The milky way total mass profile as inferred from Gaia DR2

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