Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy

Horta, Danny; Schiavon, Ricardo P.; Mackereth, J. Ted; Pfeffer, Joel; Mason, Andrew C.; Kisku, Shobhit; Fragkoudi, Francesca; Prieto, C. Allende; Cunha, Kátia; Hasselquist, Sten; Holtzman, Jon A.; Majewski, Steven R.; Nataf, David M.; O’Connell, R. W.; Schultheis, M.; Smith, Verne V.

doi:10.1093/mnras/staa2987

Cited by 174 publications

(254 citation statements)

References 125 publications

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“…Accreted stars selected via their chemistry (orange) show a large distribution of energies (−1.61 +0.22 −0.26 × 10 5 km 2 s −2 ). Comparing these values with those by Horta et al (2021), who used the same gravitational potential (McMillan 2017) within the same orbit calculation code GALPY (Bovy 2015;Mackereth & Bovy 2018) suggests a non-negligible overlap with the Inner Galaxy Structure (IGS) / Heracles they identified (Horta et al 2021). In a similar manner, we find most members of the GSE (79 per cent) tend to have orbit energies above −1.8 × 10 5 km 2 s −2 .…”

Section: Stellar Kinematics/dynamicssupporting

confidence: 75%

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: Stellar Kinematics/dynamicssupporting

confidence: 75%

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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“…This insight has allowed the unravelling of the assembly history of the Galaxy through its GC population (e.g. Kruijssen et al 2020), and predicted early accretion events which have recently been confirmed with the discovery of its stellar debris (Horta et al 2020a).…”

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confidence: 90%

Linking globular cluster formation at low and high redshift through the age–metallicity relation in E-MOSAICS

Horta

Hughes

Pfeffer

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We set out to compare the age-metallicity relation (AMR) of massive clusters from Magellanic Cloud mass galaxies in the E-MOSAICS suite of numerical cosmological simulations with an amalgamation of observational data of massive clusters in the Large and Small Magellanic Clouds (LMC/SMC). We aim to test if: i) star cluster formation proceeds according to universal physical processes, suggestive of a common formation mechanism for young-massive clusters (YMCs), intermediate-age clusters (IACs), and ancient globular clusters (GCs); ii) massive clusters of all ages trace a continuous AMR; iii) the AMRs of smaller mass galaxies show a shallower relation when compared to more massive galaxies. Our results show that, within the uncertainties, the predicted AMRs of L/SMC-mass galaxies with similar star formation histories to the L/SMC follow the same relation as observations. We also find that the metallicity at which the AMR saturates increases with galaxy mass, which is also found for the field star AMRs. This suggests that relatively low-metallicity clusters can still form in dwarfs galaxies. Given our results, we suggest that ancient GCs share their formation mechanism with IACs and YMCs, in which GCs are the result of a universal process of star cluster formation during the early episodes of star formation in their host galaxies.

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“…Through careful chemodynamical dissection, the bulge has been found to contain stars that are part of the bar, inner thin, and thick disks, as well as a pressuresupported component (Queiroz et al 2020a). Furthermore, there is evidence that the bulge also contains a remnant of a past accretion event, the inner Galaxy structure (Horta et al 2021). Multiple age studies of the bulge have reported that while the bulge is mainly composed of old stars (∼10 Gyr), it contains a nonnegligible fraction of younger stars (Bensby et al 2013(Bensby et al , 2017Schultheis et al 2017;Bovy et al 2019;Hasselquist et al 2020).…”

Section: Introductionmentioning

confidence: 99%

A2A: 21 000 bulge stars from the ARGOS survey with stellar parameters on the APOGEE scale

Wylie

Gerhard

Ness

et al. 2021

A&A

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Aims. Spectroscopic surveys have by now collectively observed tens of thousands of stars in the bulge of our Galaxy. However, each of these surveys had unique observing and data processing strategies that led to distinct stellar parameter and abundance scales. Because of this, stellar samples from different surveys cannot be directly combined. Methods. Here we use the data-driven method, The Cannon, to bring 21 000 stars from the ARGOS bulge survey, including 10 000 red clump stars, onto the parameter and abundance scales of the cross-Galactic survey, APOGEE, obtaining rms precisions of 0.10 dex, 0.07 dex, 74 K, and 0.18 dex for [Fe/H], [Mg/Fe], Teff, and log(g), respectively. The re-calibrated ARGOS survey – which we refer to as the A2A survey – is combined with the APOGEE survey to investigate the abundance structure of the Galactic bulge. Results. We find X-shaped [Fe/H] and [Mg/Fe] distributions in the bulge that are more pinched than the bulge density, a signature of its disk origin. The mean abundance along the major axis of the bar varies such that the stars are more [Fe/H]-poor and [Mg/Fe]-rich near the Galactic centre than in the outer bulge and the long bar region. The vertical [Fe/H] and [Mg/Fe] gradients vary between the inner bulge and the long bar, with the inner bulge showing a flattening near the plane that is absent in the long bar. The [Fe/H] − [Mg/Fe] distribution shows two main maxima, an ‘[Fe/H]-poor [Mg/Fe]- rich’ maximum and an ‘[Fe/H]-rich [Mg/Fe]-poor’ maximum, that vary in strength with position in the bulge. In particular, the outer long bar close to the Galactic plane is dominated by super-solar [Fe/H], [Mg/Fe]-normal stars. Stars composing the [Fe/H]-rich maximum show little kinematic dependence on [Fe/H], but for lower [Fe/H] the rotation and dispersion of the bulge increase slowly. Stars with [Fe/H] < −1 dex have a very different kinematic structure than stars with higher [Fe/H]. Conclusions. Comparing with recent models for the Galactic boxy-peanut bulge, the abundance gradients and distribution, and the relation between [Fe/H] and kinematics suggests that the stars comprising each maximum have separate disk origins with the ‘[Fe/H]-poor [Mg/Fe]-rich’ stars originating from a thicker disk than the ‘[Fe/H]-rich [Mg/Fe]-poor’ stars.

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Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy

Cited by 174 publications

References 125 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

Linking globular cluster formation at low and high redshift through the age–metallicity relation in E-MOSAICS

A2A: 21 000 bulge stars from the ARGOS survey with stellar parameters on the APOGEE scale

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