On the Use of Field RR Lyrae as Galactic Probes -- VIII. Early Formation of the Galactic Spheroid

2026/01/23 by G. Bono, V. F. Braga, M. Fabrizio +54 · 1 voice
Physics and Astronomy · #astro-ph.GA

paper · pdf · doi:10.3847/1538-4357/ae2c60

Abstract

We introduce a new photometric catalog of RR Lyrae variables (RRLs, ∼300,000) mainly based on data available in public datasets. We also present the largest and most homogeneous spectroscopic dataset of RRLs and Blue Horizontal Branch [BHB] stars ever collected. This includes radial velocity measurements (∼16,000) and iron abundances (ΔS method for 8,140 RRLs, plus 547 from literature). Elemental abundances based on high-resolution spectra are provided for 487 RRLs and 64 BHB stars. We identified candidate RRLs associated to the main Galactic components and their iron distribution function (IDF) becomes more metal-rich when moving from the Halo ([Fe/H]=-1.56) to the Thick (TCD; [Fe/H]=-1.47) and Thin (TND; [Fe/H]=-0.73) disk. Furthermore, Halo RRLs and RRLs in retrograde orbits are α-enhanced ([α/Fe]=0.27, σ=0.18), while TCD RRLs are either α-enhanced ([Fe/H]≤-1.0) or α-poor ([Fe/H]>-1.0), and TND RRLs are mainly α-poor ([α/Fe]=-0.01, σ=0.20). We also identified RRLs associated to the main stellar streams (Gaia-Sausage-Enceladus [GSE]; Sequoia, Helmi, Sagittarius) and we found that their IDFs are quite similar to Halo RRLs. However, GSE RRLs lack the metal-poor/metal-rich tails and their α-element distribution is quite compact. The iron radial gradient in Galactocentric distance for TND, TCD and Halo RRLs is negative and it decreases from -0.026, to -0.010, and to -0.002 dex/kpc. The iron radial gradient based on dry Halo (Halo without substructures) RRLs is, within the errors, equal to the global Halo. We also found a strong similarity between iron and [α/Fe] radial gradients of Milky Way RRLs and M31 globular clusters throughout the full range of galactocentric distances covered by the two samples.

Citations

• Rare Find: Discovery and chemo-dynamical properties of two s-process enhanced RR Lyrae stars
• Early Co-formation of the Milky Way's Thin and Thick Disks at Redshift z > 2
• Origin of the system of globular clusters in the Milky Way -- Gaia eDR3 edition
• The elderly among the oldest: new evidence for extremely metal-poor RR Lyrae stars
• Metallicity of RR Lyrae stars from the Gaia Data Release 3 catalogue computed with Machine Learning algorithms
• Gaia Data Release 3
• RR Lyrae and Type II Cepheid Variables in Globular Clusters: Optical and Infrared Properties
• Metallicities from high resolution spectra of 49 RR Lyrae Variables
• SDSS-IV MaNGA: Radial Gradients in Stellar Population Properties of Early-Type and Late-Type Galaxies
• The Massive M31 Cluster G1: Detailed Chemical Abundances from Integrated Light Spectroscopy
• Gaia Early Data Release 3: The astrometric solution
• On the Use of Field RR Lyrae as Galactic Probes. II. A New ΔS Calibration to Estimate Their Metallicity*
• Elemental Abundances in M31: Properties of the Inner Stellar Halo
• On the Metamorphosis of the Bailey diagram for RR Lyrae stars
• The Sixth Data Release of the Radial Velocity Experiment (RAVE) -- I: Survey Description, Spectra and Radial Velocities
• Streams, substructures and the early history of the Milky Way
• The Sixth Data Release of the Radial Velocity Experiment (RAVE) -- II: Stellar Atmospheric Parameters, Chemical Abundances and Distances
• Probing the galactic halo with RR Lyrae stars I: The catalog
• An all-sky proper motion map of the Sagittarius stream using Gaia DR2
• Local RR Lyrae Stars: native and alien
• The Metallicity Gradient and Complex Formation History of the Outermost Halo of the Milky Way
• Standard Galactic Field RR Lyrae II: A Gaia DR2 calibration of the period-Wesenheit-metallicity relation
• Dependence of Galactic Halo Kinematics on the Adopted Galactic Potential
• Resolving the Metallicity Distribution of the Stellar Halo with the H3 Survey
• Elemental Abundances in M31: A Comparative Analysis of Iron and Alpha Element Abundances in the Outer Disk, Giant Stellar Stream, and Inner Halo of M31
• Elemental Abundances in M31: First Alpha and Iron Abundance Measurements in M31's Giant Stellar Stream
• On the use of field RR Lyrae as Galactic probes: I. The Oosterhoff dichotomy based on fundamental variables
• Mapping the Stellar Halo with the H3 Spectroscopic Survey
• Infrared K_s-band Photometry of Field RR Lyrae Variable Stars
• Chemical Compositions of Field and Globular Cluster RR~Lyrae Stars: II. omega Centauri
• The Zwicky Transient Facility: Surveys and Scheduler
• Multiplicity of Galactic Cepheids and RR Lyrae stars from Gaia DR2 - I. Binarity from proper motion anomaly
• Multiplicity of Galactic Cepheids and RR Lyrae stars from Gaia DR2 -- II. Resolved common proper motion pairs
• The ASAS-SN Catalog of Variable Stars III: Variables in the Southern TESS Continuous Viewing Zone
• New Near-Infrared JHK_s light-curve templates for RR Lyrae variables
• The Zwicky Transient Facility: System Overview, Performance, and First Results
• Characterization and history of the Helmi streams with Gaia DR2
• 2D chemical evolution model: the impact of galactic disc asymmetries on azimuthal chemical abundance variations
• On a new method to estimate distance, reddening and metallicity of RR Lyrae stars using optical/near-infrared (B,V,I,J,H,K) mean magnitudes: ω Centauri as a first test case
• Mean proper motions, space orbits and velocity dispersion profiles of Galactic globular clusters derived from Gaia DR2 data
• The outer halo globular cluster system of M31 - III. Relationship to the stellar halo
• Vertical waves in the solar neighbourhood in Gaia DR2
• The shape of the Galactic halo with Gaia DR2 RR Lyrae. Anatomy of an ancient major merger
• Proper motions and dynamics of the Milky Way globular cluster system from Gaia DR2
• Chemical Compositions of Field and Globular Cluster RR Lyrae Stars: I. NGC 3201
• Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole
• Metallicity and Kinematics of the Galactic halo from the LAMOST sample stars
• Gaia Data Release 2: Specific characterisation and validation of all-sky Cepheids and RR Lyrae stars
• The Auriga Stellar Haloes: Connecting stellar population properties with accretion and merging history
• A Near-infrared RR Lyrae census along the southern Galactic plane: the Milky Way's stellar fossil brought to light
• Orbital decomposition of CALIFA spiral galaxies
• The RRC Stars: Chemical Abundances and Envelope Kinematics
• The UKIRT Hemisphere Survey: Definition and J-band Data Release
• The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the Extended Baryon Oscillation Spectroscopic Survey and from the Second Phase of the Apache Point Observatory Galactic Evolution Experiment
• Migration and kinematics in growing disc galaxies with thin and thick discs
• The structural evolution of galaxies with both thin and thick discs
• Weak Galactic Halo--Fornax dSph Connection from RR Lyrae Stars
• Spectroscopic Comparison of Metal-Rich RRab Stars of the Galactic Field with Their Metal-Poor Counterparts
• Chemical trends in the Galactic Halo with APOGEE data
• On the RR Lyrae stars in globulars: IV. ω Centauri Optical UBVRI Photometry
• Red giants observed by CoRoT and APOGEE: The evolution of the Milky Way's radial metallicity gradient
• The mass distribution and gravitational potential of the Milky Way
• Probing the early chemical evolution of the Sculptor dSph with purely old stellar tracers
• Panchromatic Hubble Andromeda Treasury XII. Mapping Stellar Metallicity Distributions in M31
• The Carina Project. VIII. The α-element abundances
• Discovery of ∼ 9,000 new RR Lyrae in the Southern Catalina Surveys
• Formation of In Situ Stellar Haloes in Milky Way-Mass Galaxies
• Integrated Light Chemical Tagging Analyses of Seven M31 Outer Halo Globular Clusters from the Pan-Andromeda Archaeological Survey
• Chemical abundances of solar neighborhood RR Lyrae stars
• galpy: A Python Library for Galactic Dynamics
• Spectroscopic Signatures of Extra-Tidal Stars Around the Globular Clusters NGC 6656 (M22), NGC 3201 and NGC 1851 from RAVE
• The Identification of RR Lyrae and Delta Scuti Stars from Variable GALEX Ultraviolet Sources
• An optimized Method to Identify RR Lyrae stars in the SDSS X Pan-STARRS1 Overlapping Area Using a Bayesian Generative Technique
• A comprehensive view of the Virgo Stellar Stream
• Mid-infrared PL relations for Globular Cluster RR Lyrae
• The Radial Velocity Experiment (RAVE): Fifth Data Release
• Stellar haloes in Milky-Way mass galaxies: From the inner to the outer haloes
• Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the Solar neighbourhood
• The Chemical Evolution of the Milky Way: the Three Infall Model
• RR Lyrae variables: visual and infrared luminosities, intrinsic colours, and kinematics
• Streams in the Aquarius stellar haloes
• Modelling the chemical evolution of the Galaxy halo
• The QUEST RR Lyrae Survey: III. The Low Galactic Latitude Catalogue
• A spectroscopic survey of Andromeda's Western Shelf
• Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS II. The complete high resolution extinction map and implications for Bulge studies
• The Kinematic Properties of BHB and RR Lyrae stars towards the Anticentre and the North Galactic Pole: The Transition between the Inner and the Outer Halo
• Global structure and kinematics of stellar haloes in cosmological hydrodynamic simulations
• The Chemical Compositions of Variable Field Horizontal Branch Stars: RR Lyrae Stars
• Exploring the Variable Sky with LINEAR. I. Photometric Recalibration with SDSS
• Orbital Eccentricity Distribution of Solar-Neighbour Halo Stars
• Fourier analysis of non-Blazhko ab-type RR Lyrae stars observed with the Kepler space telescope
• Cosmological simulations of the formation of the stellar haloes around disc galaxies
• Star Clusters in M31: II. Old Cluster Metallicities and Ages from Hectospec Data
• First stars XIII. Two extremely metal-poor RR Lyrae stars?
• On the alleged duality of the Galactic halo
• The Chemical Compositions of Non-Variable Red and Blue Field Horizontal Branch Stars
• THE WIDE-FIELD INFRARED SURVEY EXPLORER (WISE): MISSION DESCRIPTION AND INITIAL ON-ORBIT PERFORMANCE
• Quantifying the uncertainties of chemical evolution studies. II. Stellar yields
• Two distinct halo populations in the solar neighborhood. Evidence from stellar abundance ratios and kinematics
• Intrinsic iron spread and a new metallicity scale for Globular Clusters
• Riding the Spiral Waves: Implications of Stellar Migration for the Properties of Galactic Disks
• The Period-Luminosity Relation of RR Lyrae Stars in the SDSS Photometric System
• The Galaxy and its stellar halo: insights on their formation from a hybrid cosmological approach
• The Milky Way Tomography with SDSS: II. Stellar Metallicity
• The UKIDSS Galactic Plane Survey
• THE SEGUE STELLAR PARAMETER PIPELINE. I. DESCRIPTION AND COMPARISON OF INDIVIDUAL METHODS
• RR Lyrae stars in Galactic globular clusters. VI. The Period-Amplitude relation
• Two stellar components in the halo of the Milky Way
• Stellar Kinematics in the Complicated Inner Spheroid of M31: Discovery of Substructure along the Southeastern Minor Axis and Its Relationship to the Giant Southern Stream
• Kinematic Structure in the Galactic Halo at the North Galactic Pole: RR Lyrae and BHB Stars show different kinematics
• Cosmic stellar relics in the Galactic halo
• The Detailed Star Formation History in the Spheroid, Outer Disk, and Tidal Stream of the Andromeda Galaxy
• The Radial Velocity Experiment (RAVE): first data release
• Analysis of RR Lyrae Stars in the Northern Sky Variability Survey
• The Two Micron All Sky Survey (2MASS)
• Tracing Galaxy Formation with Stellar Halos I: Methods
• TheGALEXUltraviolet Variability Catalog
• Galactic Metallicity Gradients Derived from a Sample of OB Stars
• The Metal Content of the Bulge Globular Cluster NGC 6528
• Candidate RR Lyrae Stars Found in Sloan Digital Sky Survey Commissioning Data
• ROTSE All Sky Surveys for Variable Stars I: Test Fields
• Debris streams in the solar neighbourhood as relicts from the formation of the Milky Way
• Metal Rich RR Lyrae Variables: II. The Pulsational Scenario
• A Catalog of Parameters for Globular Clusters in the Milky Way
• The Chemical Evolution of the Galaxy: the two-infall model
• Metal Rich RR Lyrae Variables: I. The Evolutionary Scenario
• Compositions of halo clusters and the formation of the galactic halo
• Evidence from the motions of old stars that the Galaxy collapsed.

Discussions

• On the Use of Field RR Lyrae as Galactic Probes -- Early Formation of the Galactic Spheroid: arxiv.org/abs/2601.16523 -> RR Lyrae variables as beacons to investigate the early formation of the Milky W [bsky, 0 points, 0 comments]

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