Probing the Milky Way Halo with RR Lyrae Stars from Gaia Data Release 3

Abstract

The Milky Way (MW) stellar halo, containing debris from past accretion events, serves as a fossil record of hierarchical mass assembly. Due to their distinct properties, RR Lyrae stars (RRLs) serve as excellent tracers for identifying and characterising the halo's substructures. We analysed a sample of 4933 RRLs, for which we calculated the integrals of motion and orbital parameters. We applied the domain-informed novelty detection CLustering in Multiphase Boundaries (CLiMB) framework to identify RRL membership in the MW substructures. We analysed the metallicity distributions of RRLs in major accreted system remnants as a snapshot of their chemical evolutionary status during early epochs. We calculated the weighted mean metallicity ([Fe/H]) and the corresponding standard deviation for Gaia Sausage/Enceladus ([Fe/H] = $-1.57\pm 0.25$ dex), Sequoia ([Fe/H] =$-1.64\pm 0.26$ dex), and the Helmi streams ([Fe/H] = $-1.66\pm 0.19$ dex). The metallicity distribution of RRLs in Thamnos was found to be bimodal, with the metal-poor peak likely representing the genuine accreted Thamnos population ([Fe/H] = $-1.94\pm 0.20$ dex), in agreement with recent works based on spectroscopic abundances. Our analysis shows that the substructures ED-1 and L-RL3 are highly contaminated by thick disc stars. However, the metal-poor tails in their metallicity distributions may be signatures of remnants from small accreted systems. We also identify over-densities of RRLs in correspondence with the recently reported substructures Shiva and Shakti, which we suggest are of in-situ origin. Finally, we applied the RRL-based mass-metallicity relation of galaxies to test the nature of the identified dynamical substructures.

16 pages, 11 figures, accepted for publication in A&A

References in corpus (54)

• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Gaia Data Release 3: Summary of the content and survey properties
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• The mass distribution and gravitational potential of the Milky Way
• The GALAH Survey: Scientific Motivation
• The GALAH+ Survey: Third Data Release
• The Radial Velocity Experiment (RAVE): Fifth Data Release
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• Streams, substructures and the early history of the Milky Way
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• Kraken reveals itself -- the merger history of the Milky Way reconstructed with the E-MOSAICS simulations
• Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy
• From dawn till disk: Milky Way's turbulent youth revealed by the APOGEE+Gaia data
• Gaia Data Release 3: External calibration of BP/RP low-resolution spectroscopic data
• The chemical characterisation of halo substructure in the Milky Way based on APOGEE
• The Fall of a Giant. Chemical evolution of Enceladus, alias the Gaia Sausage
• Origin of the excess of high-energy retrograde stars in the Galactic halo
• Halo Star Streams in the Solar Neighborhood
• The GALAH Survey: Chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and $Gaia$ eDR3
• Elevated r-process enrichment in Gaia Sausage and Sequoia
• The Gaia DR3 view of dynamical substructure in the stellar halo near the Sun
• GASTRO library I: the simulated chemodynamical properties of several GSE-like stellar halos
• A massive mess: When a large dwarf and a Milky Way-like galaxy merge
• Co-formation of the thin and thick discs revealed by APOGEE-DR16 and Gaia-DR2
• The Bulge Radial Velocity Assay for RR Lyrae stars (BRAVA-RR) DR2: a Bimodal Bulge?
• The infrared JHK light curves of RR Lyr
• On the Use of Field RR Lyrae as Galactic Probes. II. A new $\Delta$S calibration to estimate their metallicity
• Photometric metallicity and distance estimates for $\sim$ 136,000 RR Lyrae stars from Gaia DR3
• Stellar halo substructure generated by bar resonances
• Substructure in the stellar halo near the Sun. II. Characterisation of independent structures
• Substructure in the stellar halo near the Sun. I. Data-driven clustering in Integrals of Motion space
• Energy wrinkles and phase-space folds of the last major merger
• Probing the galactic halo with RR Lyrae stars I: The catalog
• High-precision chemical abundances of Galactic building blocks. The distinct chemical abundance sequence of Sequoia
• RR Lyrae From Binary Evolution: Abundant, Young and Metal-Rich
• Discovery of the local counterpart of disc galaxies at z > 4: The oldest thin disc of the Milky Way using Gaia-RVS
• Metallicities from high resolution spectra of 49 RR Lyrae Variables
• VINTERGATAN-GM: The cosmological imprints of early mergers on Milky-Way-mass galaxies
• The 33 M${}_{\odot }$ black hole Gaia BH3 is part of the disrupted ED-2 star cluster
• Metallicity distributions of halo stars: do they trace the Galactic accretion history?
• The GALAH survey: Tracing the Milky Way's formation and evolution through RR Lyrae stars
• Photometric metallicity for 694233 Galactic giant stars from Gaia DR3 synthetic Stromgren photometry. Metallicity distribution functions of halo sub-structures
• Effect of orbital trapping by bar resonances in the local U-V velocity field
• The RR Lyrae Delay-Time Distribution: A Novel Perspective on Models of Old Stellar Populations
• Characterisation of local halo building blocks: Thamnos and Sequoia
• Ironing the folds: The phase space chevrons of a GSE-like merger as a dark matter subhalo detector
• Evidence of Gaia Enceladus experiencing at least two passages around the Milky Way
• How well can we unravel the accreted constituents of the Milky Way stellar halo? A test on cosmological hydrodynamical simulations
• Chronology of our Galaxy from Gaia colour-magnitude diagram fitting (ChronoGal) -- III. Age and metallicity distribution of Gaia-Sausage-Enceladus stars near the Sun
• Dynamical mirages: how bar-induced resonant trapping can mimic substructure clustering in dynamical parameter spaces
• Chemical characterisation of small substructures in the local stellar halo
• The mass-metallicity relation at z>3 down to M_*= 10^4 M_Sun. A local perspective using the metallicity distribution of RR Lyrae stars
• Stellar substructures in the Galactic disc and halo: Properties, origins, and evolution