Ironing the folds: the phase space chevrons of a GSE-like merger as a dark matter subhalo detector

Y., Davies, Elliot; Vasiliev, Eugene; Belokurov, Vasily; Evans, N. W.; M., Dillamore, Adam

doi:10.1093/mnras/stac3581

Cited by 6 publications

(2 citation statements)

References 78 publications

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“…However, the interpretation of these numerous recent discoveries can be extremely challenging. In fact, numerical simulations of a major merger between a MW-like galaxy and a GES-like progenitor have revealed that remnants from the same merging event can result in overdensities at various locations in the space defined by the IoM, which could be mistaken for independent substructures (Koppelman et al 2020;Amarante et al 2022;Belokurov et al 2023;Davies et al 2023). On the other hand, relics with different origin may significantly overlap in the IoM space (Helmi & de Zeeuw 2000;Naidu et al 2020;Lövdal et al 2022;Dodd et al 2023) and unrelated sources can drastically contaminate samples of candidate members of a given substructure selected kinematically (Buder et al 2022;Rey et al 2023).…”

Section: Introductionmentioning

confidence: 99%

A Walk on the Retrograde Side (WRS) project

Ceccarelli,

Massari,

Mucciarelli

et al. 2024

A&A

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Relics of ancient accretion events experienced by the Milky Way are predominantly located within the stellar halo of our Galaxy. However, debris from different objects display overlapping distributions in dynamical spaces, making it extremely challenging to properly disentangle their contribution to the build-up of the Galaxy. To shed light on this chaotic context, we initiated a program aimed at the homogeneous chemical tagging of the local halo of the Milky Way, focusing on the component in retrograde motion, since this is expected to host a large fraction of stars accreted from past mergers. The A Walk on the Retrograde Side (WRS) project targets retrograde halo stars in the solar neighborhood with accurate $6$D phase space information available, measuring the precise chemical abundance of several chemical elements from high-resolution spectroscopy. In this first paper, we present the project and the analysis of high-resolution spectra obtained with UVES at VLT and at LBT for $186$ stars. We obtained accurate radial velocity and chemical abundances for several elements for all the target stars. In particular, we focus on the chemical composition of a specific subset of substructures that have been dynamically identified in the literature. Our study reveals that two among the more recently discovered structures in the retrograde halo, namely, Antaeus / L-RL$64$ and ED-$3$, have identical chemical patterns and similar integrals of motion, suggesting a common origin. In turn, the abundance patterns of this unified system differ from that of Gaia-Enceladus, confirming that it is an independent structure. Finally, Sequoia exhibits a different chemistry with respect to that of Gaia-Enceladus at $ Fe/H < -1.5$ dex, showcasing an excess of stars with lower Mg and Ca in the common metallicity range.

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Section: Introductionmentioning

confidence: 99%

A Walk on the Retrograde Side (WRS) project

Ceccarelli,

Massari,

Mucciarelli

et al. 2024

A&A

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“…A recent study using local halo stars from the Gaia Data Release 3 (DR3) Radial Velocity Spectrometer (RVS) survey revealed that stars likely belonging to the GSE form several thin chevron-like overdensities in the r − v r diagram (Belokurov et al 2023). Further simulations showed that stars in the chevron-like shells conserve similar orbits of unique average energy, and the overdensities in r − v r space correspond to the bumps of stars in energy distribution (Davies et al 2023b;Belokurov et al 2023). However, their star sample is constrained to the local stellar halo, and some of the overdensities do not show an overall morphology.…”

Section: Introductionmentioning

confidence: 99%

Detection of Multiple Phase Space Overdensities of GSE Stars by Orbit Integration

Zhao

Chang

et al. 2023

ApJ

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In N-body simulations, nearly radial mergers can form shell-like overdensities in the sky position and phase space (r − v r ) due to the combination of dynamical friction and tidal stripping. The merger event of Gaia-Sausage-Enceladus (GSE) has provided a unique opportunity to study the shells in the phase space. To search for them, we integrate the orbits of 5949 GSE-related halo K giants from the LAMOST survey and record their positions at all time intervals in the r − v r diagram. After the subtraction of a smoothed background, we find six significant and complete thin chevron-like overdensities. The apocenters r apo of stars in the six chevrons are around 6.75, 12.75, 18.75, 25.25, 27.25, and 30.25 kpc. These chevrons reveal the multiple pileups of GSE stars at different apocenters. The application of a different Milky Way mass M vir will change the opening angles of these chevrons, while leaving their apocenters almost unchanged. By comparing with a recent study of the phase space overdensities of local halo stars from the Gaia Radial Velocity Spectrometer survey, our results are more inclined to a medium M vir of 1012 M ⊙. The application of a nonaxisymmetric Galactic potential with a steadily rotating bar has a blurring effect on the appearance of these chevron-like overdensities, especially for the chevrons with r apo > 20 kpc.

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Stellar halo substructure generated by bar resonances

Belokurov

Evans

et al. 2023

Monthly Notices of the Royal Astronomical Society

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Using data from the Gaia satellite’s Radial Velocity Spectrometer Data Release 3 (RVS, DR3), we find a new and robust feature in the phase space distribution of halo stars. It is a prominent ridge at constant energy and with angular momentum Lz > 0. We run test particle simulations of a stellar halo-like distribution of particles in a realistic Milky Way potential with a rotating bar. We observe similar structures generated in the simulations from the trapping of particles in resonances with the bar, particularly at the corotation resonance. Many of the orbits trapped at the resonances are halo-like, with large vertical excursions from the disc. The location of the observed structure in energy space is consistent with a bar pattern speed in the range Ωb ≈ 35 − 40 km s−1 kpc−1. Overall, the effect of the resonances is to give the inner stellar halo a mild, net spin in the direction of the bar’s rotation. As the distribution of the angular momentum becomes asymmetric, a population of stars with positive mean Lz and low vertical action is created. The variation of the average rotational velocity of the simulated stellar halo with radius is similar to the behaviour of metal-poor stars in data from the APOGEE survey. Though the effects of bar resonances have long been known in the Galactic disc, this is strong evidence that the bar can drive changes even in the diffuse and extended stellar halo through its resonances.

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Ironing the folds: the phase space chevrons of a GSE-like merger as a dark matter subhalo detector

Cited by 6 publications

References 78 publications

A Walk on the Retrograde Side (WRS) project

A Walk on the Retrograde Side (WRS) project

Detection of Multiple Phase Space Overdensities of GSE Stars by Orbit Integration

Stellar halo substructure generated by bar resonances

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