| 1. |
- Carrillo, I., et al.
(författare)
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Kinematics with GAIA DR2 : The force of a dwarf
- 2019
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 490:1, s. 797-812
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Tidskriftsartikel (refereegranskat)abstract
- We use Gaia DR2 astrometric and line-of-sight velocity information combined with two sets of distances obtained with a Bayesian inference method to study the 3D velocity distribution in the Milky Way disc. We search for variations in all Galactocentric cylindrical velocity components (Vφ, VR, and Vz) with Galactic radius, azimuth, and distance from the disc mid-plane. We confirm recent work showing that bulk vertical motions in the R–z plane are consistent with a combination of breathing and bending modes. In the x–y plane, we show that, although the amplitudes change, the structure produced by these modes is mostly invariant as a function of distance from the plane. Comparing to two different Galactic disc models, we demonstrate that the observed patterns can drastically change in short time intervals, showing the complexity of understanding the origin of vertical perturbations. A strong radial VR gradient was identified in the inner disc, transitioning smoothly from 16 km s−1 kpc−1 at an azimuth of 30◦ < φ < 45◦ ahead of the Sun-Galactic centre line to −16 km s−1 kpc−1 at an azimuth of −45◦ < φ < −30◦ lagging the solar azimuth. We use a simulation with no significant recent mergers to show that exactly the opposite trend is expected from a barred potential, but overestimated distances can flip this trend to match the data. Alternatively, using an N-body simulation of the Sagittarius dwarf–Milky Way interaction, we demonstrate that a major recent perturbation is necessary to reproduce the observations. Such an impact may have strongly perturbed the existing bar or even triggered its formation in the last 1–2 Gyr.
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| 2. |
- Sivertsson, Sofia, et al.
(författare)
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Estimating the local dark matter density in a non-axisymmetric wobbling disc
- 2022
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 511:2, s. 1977-1991
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Tidskriftsartikel (refereegranskat)abstract
- The density of dark matter near the Sun, ρDM, ⊙, is important for experiments hunting for dark matter particles in the laboratory, and for constraining the local shape of the Milky Way’s dark matter halo. Estimates to date have typically assumed that the Milky Way’s stellar disc is axisymmetric and in a steady-state. Yet the Milky Way disc is neither, exhibiting prominent spiral arms and a bar, and vertical and radial oscillations. We assess the impact of these assumptions on determinations of ρDM, ⊙ by applying a free-form, steady-state, Jeans method to two different N-body simulations of Milky Way-like galaxies. In one, the galaxy has experienced an ancient major merger, similar to the hypothesized Gaia–Sausage–Enceladus; in the other, the galaxy is perturbed more recently by the repeated passage and slow merger of a Sagittarius-like dwarf galaxy. We assess the impact of each of the terms in the Jeans–Poisson equations on our ability to correctly extract ρDM, ⊙ from the simulated data. We find that common approximations employed in the literature – axisymmetry and a locally flat rotation curve – can lead to significant systematic errors of up to a factor ∼1.5 in the recovered surface mass density ∼2 kpc above the disc plane, implying a fractional error on ρDM, ⊙ of the order of unity. However, once we add in the tilt term and the rotation curve term in our models, we obtain an unbiased estimate of ρDM, ⊙, consistent with the true value within our 95 per cent confidence intervals for realistic 20 per cent uncertainties on the baryonic surface density of the disc. Other terms – the axial tilt, 2nd Poisson and time-dependent terms – contribute less than 10 per cent to ρDM, ⊙ (given current data) and can be safely neglected for now. In the future, as more data become available, these terms will need to be included in the analysis.
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| 3. |
- Widmark, A., et al.
(författare)
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Weighing the Galactic disk using phase-space spirals II. Most stringent constraints on a thin dark disk using Gaia EDR3
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 653
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Tidskriftsartikel (refereegranskat)abstract
- Using the method that was developed in the first paper of this series, we measured the vertical gravitational potential of the Galactic disk from the time-varying structure of the phase-space spiral, using data from Gaia as well as supplementary radial velocity information from legacy spectroscopic surveys. For eleven independent data samples, we inferred gravitational potentials that were in good agreement, despite the data samples' varied and substantial selection e ffects. Using a model for the baryonic matter densities, we inferred a local halo dark matter density of 0.0085 +/- 0.0039 M(circle dot)pc(-3) = 0.32 +/- 0.15 GeV cm(-3). We were also able to place the most stringent constraint on the surface density of a thin dark disk with a scale height <= 50 pc, corresponding to an upper 95% confidence limit of roughly 5 M(circle dot)pc(-2) (compared to the previous limit of roughly 10 M(circle dot)pc(-2), given the same scale height). For the inferred halo dark matter density and thin dark disk surface density, the statistical uncertainties are dominated by the baryonic model, which potentially could also su ffer from a significant systematic error. With this level of precision, our method is highly competitive with traditional methods that rely on the assumption of a steady state. In a general sense, this illustrates that time-varying dynamical structures are not solely obstacles to dynamical mass measurements, but they can also be regarded as assets containing useful information.
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