The GALAH Survey: chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and<i>Gaia</i>eDR3

Buder, Sven; Lind, Karin; Ness, Melissa; Feuillet, Diane; Horta, Danny; Monty, Stephanie; Buck, Tobias; Nordlander, Thomas; Bland-Hawthorn, Joss; Casey, Andrew R.; Silva, Gayandhi M. De; D’Orazi, V.; Freeman, K. C.; Hayden, Michael R.; Kos, Janez; Martell, Sarah L.; Lewis, Geraint F.; Lin, Jane; Schlesinger, Katharine J.; Sharma, Sanjib; Simpson, Jeffrey D.; Stello, Dennis; Zucker, D. B.; Zwitter, T.; Ciucă, Ioana; Horner, Jonathan; Ting, Yuan-Sen; Wyse, Rosemary F. Ġ.

doi:10.1093/mnras/stab3504

Cited by 68 publications

(55 citation statements)

References 196 publications

(368 reference statements)

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“…The angular momentum restriction ensures we are not including stars on more prograde/retrograde orbits. We find that by selecting the GES substructure in this manner, we obtain a sample of stars with highly radial (J 𝑅 ∼1x10 3 kpc kms −1 ) and therefore highly eccentric (𝑒∼0.9) orbits, in agreement with selections employed in previous studies to identify this halo substructure (e.g., Mackereth & Bovy 2020;Naidu et al 2020;Feuillet et al 2021;Buder et al 2022). The final GES sample is comprised of 2,353 stars.…”

Section: Gaia-enceladus/sausagesupporting

confidence: 81%

“…Sagittarius dSph, Ibata et al 1994;Helmi stream, Helmi et al 1999), the identification of accretion events early in the life of the Milky Way has proven difficult due to phase-mixing. A possible solution to this conundrum resides in the use of additional information, typically in the form of detailed chemistry and/or ages (e.g., Nissen & Schuster 2010;Hawkins et al 2015;Hayes et al 2018;Haywood et al 2018;Mackereth et al 2019;Das et al 2020;Montalbán et al 2020;Horta et al 2021a;Hasselquist et al 2021;Buder et al 2022;Carrillo et al 2022).…”

Section: Introductionmentioning

confidence: 99%

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The chemical characterisation of halo substructure in the Milky Way based on APOGEE

Horta¹,

Schiavon²,

Mackereth³

et al. 2022

Preprint

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Galactic haloes in a Λ-Cold Dark Matter (ΛCDM) universe are predicted to host today a swarm of debris resulting from cannibalised dwarf galaxies that have been accreted via the process of hierarchical mass assembly. The chemo-dynamical information recorded in the Galactic stellar populations associated with such systems helps elucidate their nature, placing constraints on the mass assembly history of the Milky Way. Using data from the APOGEE and Gaia surveys, we examine APOGEE targets belonging to the following substructures in the stellar halo: Heracles, Gaia-Enceladus/Sausage (GES), Sagittarius dSph, the Helmi stream, Sequoia, Thamnos, Aleph, LMS-1, Arjuna, I'itoi, Nyx, Icarus, and Pontus. We examine the distributions of all substructures in chemical space, considering the abundances of elements sampling various nucleosynthetic pathways. Our main findings include: i) the chemical properties of GES, Heracles, the Helmi stream, Sequoia, Thamnos, LMS-1, Arjuna, and I'itoi match qualitatively those of dwarf satellites of the Milky Way, such as the Sagittarius dSph; ii) the abundance pattern of the recently discovered inner Galaxy substructure Heracles differs statistically from that of populations formed in situ. Heracles also differs chemically from all other substructures; iii) the abundance patterns of Sequoia (selected in various ways), Arjuna, LMS-1, and I'itoi are indistinguishable from that of GES, indicating a possible common origin; iv) the abundance patterns of the Helmi stream and Thamnos substructures are different from all other halo substructures; v) the chemical properties of Nyx and Aleph are very similar to those of disc stars, implying that these substructures likely have an in situ origin.

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Section: Gaia-enceladus/sausagesupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

The chemical characterisation of halo substructure in the Milky Way based on APOGEE

Horta¹,

Schiavon²,

Mackereth³

et al. 2022

Preprint

Self Cite

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“…The accreted component in FB20 D2 has a mean net zero rotational velocity, similarly to what is measured for the GSE (e.g. Belokurov et al 2018;Helmi et al 2018;Buder et al 2022), but model FB80 D2, which has the same satellite orbit, shows a slight retrograde net motion. This is also the case for models with dwarf D1, with the stronger feedback leading to the most retrograde realisation of the GSE.…”

Section: The Accreted Starssupporting

confidence: 59%

GASTRO library I: the simulated chemodynamical properties of several GSE-like stellar halos

Amarante,

Debattista,

Silva

et al. 2022

Preprint

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The Milky Way stellar halo contains relics of ancient mergers that tell the story of our Galaxy's formation. Some of them are identified due to their similarity in energy, actions and chemistry, referred to as the "chemodynamical space", and are often attributed to distinct merger events. It is also known that our Galaxy went through a significant merger event that shaped the local stellar halo during its first Gyr. Previous studies using N -body only and cosmological hydrodynamical simulations have shown that such single massive merger can produce several "signatures" in the chemodynamical space, which can potentially be misinterpreted as distinct merger events. Motivated by these, in this work we use a subset of the GASTRO library which consists of several SPH+N -body models of single accretion event in a Milky Way-like galaxy. Here, we study models with orbital properties similar to the main merger event of our Galaxy and explore the implications to known stellar halo substructures. We find that: i. supernova feedback efficiency influences the satellite's structure and orbital evolution, resulting in distinct chemodynamical features for models with the same initial conditions, ii. very retrograde high energy stars are the most metal-poor of the accreted dwarf galaxy and could be misinterpreted as a distinct merger iii. the most bound stars are more metal-rich in our models, the opposite of what is observed in the Milky Way, suggesting a secondary massive merger, and finally iv. our models can reconcile other known substructures to an unique progenitor.

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“…This is especially promising as Das et al (2020) showed that using this combination of abundances, their sample of accreted stars have older ages (see their Figure 7) and kinematics (see their Figure 8) similar to accreted stars in the literature (e.g., Belokurov et al 2018). Whether selecting dynamically or chemically gives a cleaner or different sample of accreted stars is worth exploring and has been the subject of the work from Buder et al (2022). Using GALAH DR3 data and the combination of [Na/Fe] and [Mg/Mn], the authors found that their GES sample from a chemical selection overlaps with 29% of a pure dynamicallyselected sample, as suggested by Feuillet et al (2021).…”

Section: Accreted Stars Selectionmentioning

confidence: 92%

The detailed chemical abundance patterns of accreted halo stars from the optical to infrared

Carrillo,

Hawkins,

Jofré

et al. 2022

Preprint

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Understanding the assembly of our Galaxy requires us to also characterize the systems that helped build it. In this work, we accomplish this by exploring the chemistry of accreted halo stars from the Gaia-Enceladus/Gaia-Sausage (GES) selected in the infrared from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) Data Release 16. We use high resolution optical spectra for 62 GES stars to measure abundances in 20 elements spanning the 𝛼, Fe-peak, light, odd-Z, and notably, the neutron-capture groups of elements to understand their trends in the context of and in contrast to the Milky Way and other stellar populations. Using these derived abundances we find that the optical and the infrared abundances agree to within 0.15 dex except for O, Co, Na, Cu, and Ce. These stars have enhanced neutroncapture abundance trends compared to the Milky Way, and their [Eu/Mg] and neutron-capture abundance ratios (e.g., [Y/Eu], [Ba/Eu], [Zr/Ba], [La/Ba], and [Nd/Ba]) point to r-process enhancement and a delay in s-process enrichment. Their [𝛼/Fe] trend is lower than the Milky Way trend for [Fe/H]>-1.5 dex, similar to previous studies of GES stars and consistent with the picture that these stars formed in a system with a lower rate of star formation. This is further supported by their depleted abundances in Ni, Na, and Cu abundances, again, similar to previous studies of low-𝛼 stars with accreted origins.

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

Cited by 68 publications

References 196 publications

The chemical characterisation of halo substructure in the Milky Way based on APOGEE

The chemical characterisation of halo substructure in the Milky Way based on APOGEE

GASTRO library I: the simulated chemodynamical properties of several GSE-like stellar halos

The detailed chemical abundance patterns of accreted halo stars from the optical to infrared

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