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The oldest stars in the Milky Way (born in the first few billion years) are expected to have a high density in the inner few kpc, spatially overlapping with the Galactic bulge. We use spectroscopic data from the Pristine Inner Galaxy Survey (PIGS) to study the dynamical properties of ancient, metal-poor inner Galaxy stars. We compute distances using starhorse , and orbital properties in a barred Galactic potential. With this paper, we release the spectroscopic AAT/PIGS catalogue (13 235 stars). We find that most PIGS stars have orbits typical for a pressure-supported population. The fraction of stars confined to the inner Galaxy decreases with decreasing metallicity, but many very metal-poor stars (VMP; [Fe/H] <−2.0) stay confined (⁠|$\sim 60~{{\ \rm per \, cent}}$| stay within 5 kpc). The azimuthal velocity vϕ also decreases between [Fe/H] = −1.0 and −2.0, but is constant for VMP stars (at ∼+40 km s−1). The carbon-enhanced metal-poor (CEMP) stars in PIGS appear to have similar orbital properties compared to normal VMP stars. Our results suggest a possible transition between two spheroidal components – a more metal-rich, more concentrated, faster rotating component, and a more metal-poor, more extended and slower/non-rotating component. We propose that the former may be connected to pre-disc in-situ stars (or those born in large building blocks), whereas the latter may be dominated by contributions from smaller galaxies. This is an exciting era where large metal-poor samples, such as in this work (as well as upcoming surveys, e.g. 4MOST), shed light on the earliest evolution of our Galaxy. [ABSTRACT FROM AUTHOR]

Using N -body simulations, we demonstrate that satellite dwarf galaxy pairs which undergo significant mixing (∼6 Gyr) can have their respective most bound particles separated great distances upon subsequently merging with a more massive host. This may provide an explanation as to the origin of the complex globular cluster NGC 2419, which is found within the tail of the Sagittarius dwarf spheroidal galaxy, yet separated from its central remnant by over 100 kpc. Dynamical investigations could support the chemical evidence which already points to the NGC 2419 being a nuclear star cluster. Motivated by the distinct nature of NGC 2419, we run a suite of simulations whereby an initial pre-infall merger of two satellites is followed by a post-infall merger of the remnant into a Milky Way-like host potential. We present a striking example from our suite in this work, in which this separation is reproduced by the most bound particles of the two pre-infall satellites. Additionally, this double merger scenario can induce unusual on-sky features in the tidal debris of the post-infall merger, such as clouds, overdensities, and potentially new arms that could resemble the bifurcation observed in Sagittarius. [ABSTRACT FROM AUTHOR]

In this study we combine asteroseismic, spectroscopic, and kinematic information to perform a detailed analysis of a sample of 16 stars from the Kepler field. Our selection focuses on stars that appear to contradict Galactic chemical evolution models: young and α-rich, old and metal-rich, as well as other targets with unclear classification in past surveys. Kinematics are derived from Gaia DR3 parallaxes and proper motions, and high-resolution spectra from HIRES/Keck are used to calculate chemical abundances for over 20 elements. This information is used to perform careful checks on asteroseismic masses and ages derived via grid-based modelling. Among the seven stars previously classified as young and α-rich, only one seems to be an unambiguously older object masking its true age. We confirm the existence of two very old (≥11 Gyr), super metal-rich (≥0.1 dex) giants. These two stars have regular thin disc chemistry and in-plane solar circle orbits that fit well in the picture of radial migration via the churning mechanism. The alternative explanation that these stars have younger ages would require mass-loss rates that strongly increase with increasing metallicity. Finally, we suggest further investigations to explore the suitability of Zn as a chemical clock in red giants. [ABSTRACT FROM AUTHOR]

In this work, we combine information from solar-like oscillations, high-resolution spectroscopy, and Gaia astrometry to derive stellar ages, chemical abundances, and kinematics for a group of seven metal-poor red giants and characterize them in a multidimensional chrono-chemo-dynamical space. Chemical abundance ratios were derived through classical spectroscopic analysis employing 1D LTE atmospheres on Keck/HIRES spectra. Stellar ages, masses, and radii were calculated with grid-based modelling, taking advantage of availability of asteroseismic information from Kepler. The dynamical properties were determined with galpy using Gaia EDR3 astrometric solutions. Our results suggest that underestimated parallax errors make the effect of Gaia parallaxes more important than different choices of model grid or – in the case of stars ascending the red giant branch – mass-loss prescription. Two of the stars in this study are identified as potentially evolved halo blue stragglers. Four objects are likely members of the accreted Milky Way halo, and their possible relationship with known accretion events is discussed. [ABSTRACT FROM AUTHOR]

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 |$\gt 10^{10}\, \mathrm{M_\odot }$| 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] versus [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 |$30 \lt \sqrt{J_R / \, \mathrm{kpc\, km\, s^{-1}}} \lt 55$|⁠ , we can characterize an unprecedented 24 abundances of this structure with GALAH+ DR3. With our chemical selection we characterize the dynamical properties of the GSE, for example mean |$\sqrt{J_R / \, \mathrm{kpc\, km\, s^{-1}}} =$| |$26_{-14}^{+9}$|⁠. We find only |$(29\pm 1){{\ \rm per\ cent}}$| 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. [ABSTRACT FROM AUTHOR]