Transient spiral structure and the disc velocity substructure in Gaia DR2

Hunt, Jason A. S.; Hong, Jack; Bovy, Jo; Kawata, Daisuke; Grand, Robert J. J.

doi:10.1093/mnras/sty2532

Cited by 108 publications

(101 citation statements)

References 61 publications

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“…The smooth variation of velocity dispersion as a function of chemistry is a surprising result, given the incredible amount of substructure in velocity space found locally (e.g. Antoja et al 2018;Hunt et al 2018;Quillen et al 2018;Trick et al 2018;Bland-Hawthorn et al 2019). In particular, for the vertical velocity dispersion, no metallicity bin (aside from the most metal-rich stellar populations) crosses another metallicity bin in velocity dispersion as a function of [α/Fe].…”

Section: Discussionmentioning

confidence: 99%

The GALAH survey: chemodynamics of the solar neighbourhood

Hayden

Bland-Hawthorn

Sharma

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We present the chemodynamic structure of the solar neighbourhood using 55 652 stars within a 500 pc volume around the Sun observed by GALAH and with astrometric parameters from Gaia DR2. We measure the velocity dispersion for all three components (vertical, radial, and tangential) and find that it varies smoothly with [Fe/H] and [α/Fe] for each component. The vertical component is especially clean, with $\sigma _{v_z}$ increasing from a low of 10 km s−1 at solar [α/Fe] and [Fe/H] to a high of more than 50 km s−1 for more metal-poor and [α/Fe] enhanced populations. We find no evidence of a large decrease in the velocity dispersion of the highest [α/Fe] populations as claimed in surveys prior to Gaia DR2. The eccentricity distribution for local stars varies most strongly as a function of [α/Fe], where stars with [α/Fe] < 0.1 dex having generally circular orbits (e < 0.15), while the median eccentricity increases rapidly for more [α/Fe] enhanced stellar populations up to e ∼ 0.35. These [α/Fe] enhanced populations have guiding radii consistent with origins in the inner Galaxy. Of the stars with metallicities much higher than the local interstellar medium ([Fe/H] > 0.1 dex), we find that the majority have e < 0.2 and are likely observed in the solar neighbourhood through churning/migration rather than blurring effects, as the epicyclic motion for these stars is not large enough to reach the radii at which they were likely born based on their metallicity.

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Section: Discussionmentioning

confidence: 99%

The GALAH survey: chemodynamics of the solar neighbourhood

Hayden

Bland-Hawthorn

Sharma

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Such deviations can arise from the dynamics of the spiral arms (e.g. Kawata et al 2018;Hunt et al 2018), perturbations to the disc from the Sagittarius and LMC dwarfs (e.g. Gómez et al 2017;Laporte et al 2018), or from departures of the DM halo from equilibrium due to the recent accretion of the LMC (e.g.…”

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

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319

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 trends in the velocity structure relating to this perturbation have also been studied in great detail (e.g. Gaia Collaboration et al 2018b;Hunt et al 2018;Carrillo et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Vertical waves in the solar neighbourhood inGaiaDR2

Bennett

Bovy

2018

Monthly Notices of the Royal Astronomical Society

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370

233

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The vertical distribution of stars in the solar neighbourhood is not in equilibrium but contains a wave signature in both density and velocity space originating from a perturbation. With the discovery of the phase-space spiral in Gaia data release 2, determining the origin of this perturbation has become even more urgent. We develop and test a fast method for calculating the perturbation from a passing satellite on the vertical component of a part of a disc galaxy. This fast method allows us to test a large variety of possible perturbations to the vertical disc very quickly. We apply our method to the range of possible perturbations to the solar neighbourhood stemming from the recent passage of the Sagittarius dwarf galaxy (Sgr), varying its mass, mass profile, and present-day position within their observational uncertainties, and its orbit within different realistic models for the Milky Way's gravitational potential. We find that we are unable to reproduce the observed asymmetry in the vertical number counts and its concomitant breathing mode in velocity space for any plausible combination of Sgr and Milky-Way properties. Both the amplitude and the period of the number-count asymmetry and of the oscillations in the mean vertical velocity produced by the passage of Sgr is in large disagreement with the observations from Gaia DR2. We conclude that Sgr cannot have caused the observed oscillations in the vertical disc or the Gaia phase-space spiral.

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Transient spiral structure and the disc velocity substructure in Gaia DR2

Cited by 108 publications

References 61 publications

The GALAH survey: chemodynamics of the solar neighbourhood

The GALAH survey: chemodynamics of the solar neighbourhood

The milky way total mass profile as inferred from Gaia DR2

Vertical waves in the solar neighbourhood inGaiaDR2

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