Dynamically Tagged Groups of Very Metal-poor Halo Stars from the HK and Hamburg/ESO Surveys

Abstract

We analyze the dynamical properties of $\sim$1500 very metal-poor (VMP; [Fe/H] $\lesssim -2.0$) halo stars, based primarily on medium-resolution spectroscopic data from the HK and Hamburg/ESO surveys. These data, collected over the past thirty years, are supplemented by a number of calibration stars and other small samples, along with astrometric information from $Gaia$ DR2. We apply a clustering algorithm to the 4-D energy-action space of the sample, and identify a set of 38 Dynamically Tagged Groups (DTGs), containing between 5 and 30 member stars. Many of these DTGs can be associated with previously known prominent substructures such as $Gaia$-Sausage/Enceladus (GSE), Sequoia, the Helmi Stream (HStr), and Thamnos. Others are associated with previously identified smaller dynamical groups of stars and streams. We identify 10 new DTGs as well, many of which have strongly retrograde orbits. We also investigate possible connections between our DTGs and $\sim$300 individual $r$-process-enhanced (RPE) stars from a recent literature compilation. We find that several of these objects have similar dynamical properties to GSE (5), the HStr (4), Sequoia (1), and Rg5 (1), indicating that their progenitors might have been important sources of RPE stars in the Galaxy. Additionally, a number of our newly identified DTGs are shown to be associated with at least two RPE stars each (DTG-2: 3, DTG-7: 2; DTG-27: 2). Taken as a whole, these results are consistent with ultra-faint and/or dwarf spheroidal galaxies as birth environments in which $r$-process nucleosynthesis took place, and then were disrupted by the Milky Way.

Accepted for ApJ. Tables 5 and 6 available in the online journal. Minor typos fixed and references updated to match published version

References in corpus (41)

• The NumPy array: a structure for efficient numerical computation
• The Gaia mission
• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• The mass distribution and gravitational potential of the Milky Way
• Two Stellar Components in the Halo of the Milky Way
• Nucleosynthetic signatures of the first stars
• The SEGUE Stellar Parameter Pipeline. I. Description and Initial Validation Tests
• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars
• Streams, substructures and the early history of the Milky Way
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances
• The SEGUE Stellar Parameter Pipeline. II. Validation with Galactic Globular and Open Clusters
• Kraken reveals itself -- the merger history of the Milky Way reconstructed with the E-MOSAICS simulations
• The stellar halo of the Galaxy
• The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars
• Bright Metal-Poor Stars from the Hamburg/ESO Survey. I. Selection and Follow-up Observations from 329 Fields
• The LAMOST Stellar Parameter Pipeline at Peking University --- LSP3
• Disentangling the Galactic Halo with APOGEE: I. Chemical and Kinematical Investigation of Distinct Metal-Poor Populations
• New Extremely Metal-Poor Stars in the Galactic Halo
• An R-process enhanced star in the dwarf galaxy Tucana III
• A box full of chocolates: The rich structure of the nearby stellar halo revealed by Gaia and RAVE
• Halo Substructure in the SDSS-Gaia Catalogue : Streams and Clumps
• The SkyMapper-Gaia RVS view of the Gaia-Enceladus-Sausage -- an investigation of the metallicity and mass of the Milky Way's last major merger
• The $R$-Process Alliance: Fourth Data Release from the Search for $r$-Process-Enhanced Stars in the Galactic Halo
• Timing the Early Assembly of the Milky Way with the H3 Survey
• Origin of the excess of high-energy retrograde stars in the Galactic halo
• A Sequoia in the Garden: FSR 1758 - Dwarf Galaxy or Giant Globular Cluster?
• A Low-Mass Stellar-Debris Stream Associated with a Globular Cluster Pair in the Halo
• The Pristine survey X: a large population of low-metallicity stars permeates the Galactic disk
• Population Studies. XIII. A New Analysis of the Bidelman-MacConnell "Weak-Metal" Stars - Confirmation of Metal-Poor Stars in the Thick Disk of the Galaxy
• The R-process Alliance: First Magellan/MIKE Release from the Southern Search for R-Process-enhanced Stars
• Bright Metal-Poor Stars from the Hamburg/ESO Survey. II. A Chemodynamical Analysis
• Abundances and kinematics of carbon-enhanced metal-poor stars in the Galactic halo*; A new classification scheme based on Sr and Ba
• The tale of the tail -- disentangling the high transverse velocity stars in Gaia DR2
• Chemical Cartography. I. A Carbonicity Map of the Galactic Halo
• The S2 Stream: the shreds of a primitive dwarf galaxy
• Chemical Cartography. II. The Assembly History of the Galactic Stellar Halo Traced by Carbon-Enhanced Metal-Poor Stars
• Dependence of Galactic Halo Kinematics on the Adopted Galactic Potential

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• The R-Process Alliance: Chemo-Dynamically Tagged Groups II. An Extended Sample of Halo $r$-Process-Enhanced Stars
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• Phase-space Properties and Chemistry of the Sagittarius Stellar Stream Down to the Extremely Metal-poor ($[Fe/H]\lesssim -3$) Regime
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• Four-hundred Very Metal-poor Stars Studied with LAMOST and Subaru. III. Dynamically Tagged Groups and Chemodynamical Properties
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• $S^5$: The destruction of a bright dwarf galaxy as revealed by the chemistry of the Indus stellar stream
• Iron-Peak Element Abundances in Warm Very Metal-Poor Stars
• Using Action Space Clustering to Constrain the Accretion History of Milky Way like Galaxies
• On the likelihoods of finding very metal-poor (and old) stars in the Milky Way's disc, bulge, and halo
• Robust Clustering of the Local Milky Way Stellar Kinematic Substructures with Gaia eDR3
• Chemo-dynamics and asteroseismic ages of seven metal-poor red giants from the Kepler field
• The S-PLUS Ultra-Short Survey: first data release
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• Chemodynamical Properties and Ages of Metal-Poor Stars in S-PLUS
• Discovery of a pair of very metal-poor stars enriched in neutron-capture elements: The proto-disk r-II star BPS CS 29529-0089 and the Gaia-Sausage-Enceladus r-I star TYC 9219-2422-1
• A chemodynamical analysis of bright metal-poor stars from the HESP-GOMPA survey -- Indications of a non-prevailing site for light r-process elements
• Combining Astrometry and Elemental Abundances: The Case of the Candidate Pre-Gaia Halo Moving Groups G03-37, G18-39, and G21-22
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