Frequencies, chaos, and resonances: A study of orbital parameters of nearby thick-disc and halo stars

Koppelman, Helmer H.; Hagen, Jorrit H. J.; Helmi, Amina

doi:10.1051/0004-6361/202039390

Cited by 14 publications

(17 citation statements)

References 84 publications

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“…Similar to Mg, we see that the accreted stars of the GSE, independent of their selection, are lower in their α-process element abundances than the high-α disc, as already found in previous studies (Venn et al 2004;Nissen & Schuster 2010;Hawkins et al 2015;Hayes et al 2018;Koppelman et al 2019;Mackereth et al 2019;Di Matteo et al 2020;Koppelman, Hagen & Helmi 2021;Matsuno et al 2021;Recio-Blanco et al 2021). We have shown a decreasing separation significance r in Table 1 from Mg to Ca, with exception of the more precisely measured element Ti.…”

Section: Telltale Elements Of Accretion Based On Galah+ Dr3supporting

confidence: 87%

“…Zolotov et al 2010;Buck 2020;Grand et al 2020;Renaud et al 2021a), the estimation of infall scenarios and parameters of the GSE (e.g. Villalobos & Helmi 2008;Koppelman et al 2021;Naidu et al 2021), including the amount and importance of gas-rich and gas-poor mergers (e.g. Fensch et al 2017;Renaud et al 2021b) and telling apart different components of simulated galaxies (e.g.…”

Section: O U T L O O Kmentioning

confidence: 99%

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The GALAH Survey: chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 andGaiaeDR3

Buder

Lind

Ness

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Since the advent of Gaia astrometry, it is possible to identify massive accreted systems within the Galaxy through their unique dynamical signatures. One such system, Gaia-Sausage-Enceladus (GSE), appears to be an early “building block” given its virial mass >1010 M⊙ at infall (z ∼ 1 − 3). In order to separate the progenitor population from the background stars, we investigate its chemical properties with up to 30 element abundances from the GALAH+ Survey Data Release 3 (DR3). To inform our choice of elements for purely chemically selecting accreted stars, we analyse 4164 stars with low-α abundances and halo kinematics. These are most different to the Milky Way stars for abundances of Mg, Si, Na, Al, Mn, Fe, Ni, and Cu. Based on the significance of abundance differences and detection rates, we apply Gaussian mixture models to various element abundance combinations. We find the most populated and least contaminated component, which we confirm to represent GSE, contains 1049 stars selected via [Na/Fe] vs. [Mg/Mn] in GALAH+ DR3. We provide tables of our selections and report the chrono-chemodynamical properties (age, chemistry, and dynamics). Through a previously reported clean dynamical selection of GSE stars, including $30 < \sqrt{J_R / \, \mathrm{kpc\, km\, s^{-1}}} < 55$, we can characterise an unprecedented 24 abundances of this structure with GALAH+ DR3. With our chemical selection we characterise the dynamical properties of the GSE, for example mean $\sqrt{J_R / \, \mathrm{kpc\, km\, s^{-1}}} = 26^{+9}_ {-14}$. We find only $(29\pm 1)\%$ of the GSE stars within the clean dynamical selection region. Our methodology will improve future studies of accreted structures and their importance for the formation of the Milky Way.

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Section: Telltale Elements Of Accretion Based On Galah+ Dr3supporting

confidence: 87%

Section: O U T L O O Kmentioning

confidence: 99%

The GALAH Survey: chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 andGaiaeDR3

Buder

Lind

Ness

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…The underlying (static) Galactic potential can also cause "observable" substructure in the space of orbital parameters. For example, Amarante et al (2020) and Koppelman et al (2021) have shown that the wedges seen in z max -r max space (see e.g. Haywood et al 2018) are related to the transitions between different orbital families associated to resonances and chaotic regions in our galaxy.…”

Section: Introductionmentioning

confidence: 94%

“…We investigate the frequencies of the orbits by using a variation on the cylindrical polar coordinates (namely Poincaré's symplectic polar variables) following Valluri et al (2012) and Koppelman et al (2021). We input the positions and velocities in this coordinate system as complex time series into SuperFreq (Price-Whelan 2015), that numerically calculates the frequencies; Ω z , Ω R , Ω φ .…”

Section: Frequency Analysismentioning

confidence: 99%

Substructures, Resonances and debris streams

Dodd,

Helmi,

Koppelman

2021

Preprint

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Context. The local stellar halo of the Milky Way contains the debris from several past accretion events.Aims. Here we study in detail the structure and properties of nearby debris associated with the Helmi streams, originally identified as an overdensity in integrals of motion space. Methods. We use 6D phase-space information from Gaia EDR3 combined with spectroscopic surveys, and we analyse the orbits and frequencies of the stars in the streams using various Galactic potentials. Results. We find that the streams are split into substructures in integrals of motion space, most notably into two clumps in angular momentum space. The clumps have consistent metallicity distributions and stellar populations, supporting a common progeny. In all the realistic Galactic potentials explored, the Helmi streams stars are on different orbital families and spread across multiple resonances. For example, ∼ 40% of the streams stars populate the Ω z : Ω R ∼ 1:2 resonance tightly, while the remainder depict a more diffuse distribution close to Ω z /Ω R ∼ 0.7. At the same time, the reason for the substructure in angular momentum space appears to be due to a Ω z : Ω φ resonance close to the 1:1. There is also substructure in velocity space which can be related to the presence of these multiple resonances. Conclusions. Our findings suggest that the structure of the Galactic potential leaves a clear imprint on the properties of phase-mixed debris streams, and as a consequence, that these are more complex than considered thus far. It is however not clear why the particular resonances identified are populated as observed.

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“…Based on these astrometry data of stars in Gaia catalog combined with spectroscopic catalogs, the MW's new dynamical maps have been drawn (e.g. Helmi et al 2018;Belokurov et al 2018;Myeong et al 2018a,b;Beane et al 2019;Hagen et al 2019;Anguiano et al 2020;Cordoni et al 2021;Koppelman et al 2021), and new aspects of the MW's formation and evolution history have been revealed (e.g. Antoja et al 2018;Sestito et al 2019;Wyse 2019).…”

Section: Introductionmentioning

confidence: 99%

The global structure of the Milky Way's stellar halo based on the orbits of local metal-poor stars

Sato,

Chiba

2021

Preprint

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We analyze the global structure of the Milky Way (MW)'s stellar halo including its dominant subcomponent, Gaia-Sausage-Enceladus (GSE). The method to reconstruct the global distribution of this old stellar component is to employ the superposition of the orbits covering over the large MW's space, where each of the orbit-weighting factor is assigned following the probability that the star is located at its currently observed position. The selected local, metal-poor sample with [Fe/H] < −1 using Gaia EDR3 and SDSS DR16 shows that the global shape of the halo is systematically rounder at all radii in more metal-poor ranges, such that an axial ratio, q, is nearly 1 for [Fe/H] < −2.2 and ∼ 0.7 for −1.4 < [Fe/H] < −1.0. It is also found that a halo in relatively metal-rich range of [Fe/H] > −1.8 actually shows a boxy/peanut-like shape, suggesting a major merger event. The distribution of azimuthal velocities shows a disk-like flattened structure at −1.4 < [Fe/H] < −1.0, which is thought to be the metal-weak thick disk. For the subsample of stars showing GSE-like kinematics and at [Fe/H] > −1.8, its global density distribution is more spherical with q ∼ 0.9 than the general halo sample, having an outer ridge at r ∼ 20 kpc. This spherical shape is consistent with the feature of accreted halo components and the ridge suggests that the orbit of GSE's progenitor has an apocenter of ∼ 20 kpc. Implications for the formation of the stellar halo are also presented.

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Frequencies, chaos, and resonances: A study of orbital parameters of nearby thick-disc and halo stars

Cited by 14 publications

References 84 publications

The GALAH Survey: chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 andGaiaeDR3

The GALAH Survey: chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 andGaiaeDR3

Substructures, Resonances and debris streams

The global structure of the Milky Way's stellar halo based on the orbits of local metal-poor stars

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