J/A+A/708/A384 Milky Way halo Gaia DR3 RR Lyrae stars (Muraveva+, 2026)
Probing the Milky Way halo with RR Lyrae stars from Gaia Data Release 3.
Muraveva T., Monti L., Massari D., De Leo M., Garofalo A., Clementini G.,
Ceccarelli E., Michelucci U.
<Astron. Astrophys. 708, A384 (2026)>
=2026A&A...708A.384M 2026A&A...708A.384M (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, variable ; Proper motions ;
Abundances, [Fe/H] ; Optical
Keywords: techniques: photometric - stars: abundances -
stars: variables: RR Lyrae - Galaxy: halo
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 sub-structures.
Thanks to the advent of Gaia Data Release 3 (DR3), which includes
high-precision positions, parallaxes, proper motions, and radial
velocities, along with the identification and characterisation of
thousands of RRLs, it has become possible to study the distribution,
kinematics, and metallicity of RRLs in the various dynamical
sub-structures with unprecedented detail.
Our primary goal is to identify and characterise the dynamical
sub-structures of the MW halo using RRLs from Gaia DR3. Methods. 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 sub-structures. We then
used newly calibrated photometric metallicities available in the
literature to study the metallicity distributions of RRLs in different
sub-structures.
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±0.25dex), Sequoia
([Fe/H]=-1.64±0.26dex), and the Helmi streams
([Fe/H]=-1.66±0.19dex). The metallicity distribution of RRLs in
Thamnos was found to be bimodal, with the metal-poor peak likely
representing the genuine (i.e. true) accreted Thamnos population
([Fe/H]=-1.94±0.20dex), in agreement with recent works based on
spectroscopic abundances. Our analysis shows that the sub-structures
ED-1 and L-RL3 are highly contaminated by thick-disc stars. However,
the metal-poor tails in their metallicity distributions might be
signatures of remnants from small accreted systems. We also identified
some over-densities of RRLs in correspondence with the recently
reported sub-structures Shiva and Shakti, which we suggest are of an
in situ origin. Finally, we applied the RRL-based mass-metallicity
relation of galaxies to test the nature of the identified dynamical
sub-structures.
Description:
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 sub-structures.
We then analysed the metallicity distributions of RRLs in major
accreted system remnants as a snapshot of their chemical evolutionary
status during early epochs.
Parameters of the 4933 RR Lyrae stars in the reference sample.
Column (1) Gaia DR3 identification number; (2) and (3) Coordinates;
(4) and (5) Proper motions; (6) Angular momentum along the Z-axis; (7)
Total energy; (8) Component of angular momentum perpendicular to Lz;
(9) Eccentricity; (10) and (11) Photometric metallicities and their
corresponding uncertainties; (12) The sub-structure to which the star
is assigned by the CLiMB algorithm.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 112 4933 Parameters of the 4933 RR Lyrae stars in the
reference sample
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR3 Gaia DR3 source identifier
21- 28 F8.4 deg RAdeg Right Ascension (ICRS) at Ep=2016.0
30- 37 F8.4 deg DEdeg Declination (ICRS) at Ep=2016.0
39- 47 F9.4 mas/yr pmRA Proper motion in right ascension direction
49- 57 F9.4 mas/yr pmDE Proper motion in declination direction
59- 65 F7.1 kpc.km/s Lz Angular momentum along the Z-axis
67- 75 F9.1 km2/s2 E Total energy
77- 82 F6.1 kpc.km/s Lperp Component of angular momentum perpendicular
to Lz
84- 87 F4.2 --- ecc Eccentricity
89- 93 F5.2 [-] [Fe/H] ?=- Photometric metallicity
95- 98 F4.2 [-] e_[Fe/H] ?=- Uncertainty of the photometric
metallicity
100-112 A13 --- Substruc Name of the sub-structure
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Acknowledgements:
Tatiana Muraveva, tatiana.muraveva(at)inaf.it
License: CC-BY-4.0
(End) Tatiana Muraveva [INAF - OAS Bologna], Patricia Vannier [CDS] 22-Apr-2026