J/A+A/706/A195 Pristine survey. XXVIII. (Viswanathan+, 2026)
The Pristine survey. XXVIII. Journey to the Galactic outskirts.
Mapping the outer halo red giant stars down to the very metal-poor end.
Viswanathan A., Bystroem A., Starkenburg E., Foppen A., Straat J.,
Montelius M., Sestito F., Venn K.A., Navarrete C., Matsuno T., Martin N.F.,
Thomas G.F., Ardern-Arentsen A., Battaglia G., Fouesneau M., Navarro J.,
Vitali S.
<Astron. Astrophys. 706, A195 (2026)>
=2026A&A...706A.195V 2026A&A...706A.195V (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Stars, distances ; Extinction ; Radial velocities ;
Optical ; Abundances, [Fe/H]
Keywords: methods: data analysis - Galaxy: formation - Galaxy: halo -
Galaxy: kinematics and dynamics - Galaxy: stellar content -
Galaxy: structure
Abstract:
The outer Galactic halo remains relatively unexplored, particularly
regarding its metallicity distribution, merger debris, and the
population of very and extremely metal-poor ([Fe/H]←2.5) stars.
Using photometric metallicities from the Pristine survey data release
1 (PDR1) and Pristine- synthetic (PGS) catalogue and DR3 astrometry,
we constructed well-characterised samples of bright (G<17.6) red
giant branch (RGB) stars in the outer halo. With accurate distances,
these samples enable studies of the halo's metallicity distribution,
accreted debris, and very metal-poor (VMP) substructures beyond 40
kpc.
We selected giants by excluding stars with reliable parallaxes in
brightness ranges where dwarfs are measurable. Purity and completeness
were validated against the Pristine spectroscopic training set.
Distances were derived using BaSTI isochrone fitting combined with
Pristine metallicity estimates.
The photometric distances reach ∼100kpc (PDR1) and ∼70kpc (PGS),
with typical uncertainties of 12% and scatter up to 20-40% compared to
parallax- and StarHorse-based distances. The PDR1 sample provides a
nearly unbiased metallicity-distance view, while the PGS sample
offers an all-sky map, especially at the very metal-poor end. Using
PDR1-giants, we traced the halo metallicity distribution function out
to 101 kpc, fitting a three-component Gaussian mixture model. The most
metal-poor component becomes increasingly dominant with distance, as
beyond 50kpc, 40-50% of the stars are very metal-poor ([Fe/H]←2.0).
With added radial velocities, we identified metallicity trends in
integrals-of-motion space and investigated accreted debris. The PGS
sample reveals substructures, including the Pisces Plume, where 41 VMP
stars are linked to the Magellanic stream.
We publish two RGB catalogues: PDR1-giants (180314 stars, with 10096
very metal-poor candidates and 2096 beyond 40kpc) and PGS-giants
(2420898 stars, with 75679 very metal-poor candidates and 267
beyond 40kpc). These catalogues represent extensive resources for
future outer halo studies.
Description:
RGB catalogues: PDR1-giants (180314 stars, with 10096 very metal-poor
candidates and 2096 beyond 40kpc) and PGS-giants (2420898 stars, with
75679 very metal-poor candidates and 267 beyond 40kpc).RGB catalogues:
PDR1-giants (180314 stars, with 10096 very metal-poor candidates and
2096 beyond 40kpc) and PGS-giants (2420,898 stars, with 75679 very
metal-poor candidates and 267 beyond 40kpc).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
rgb-pdr1.dat 378 410812 PDR1-giants (180314 stars, with 10096 very
metal-poor candidates and 2096 beyond 40kpc)
catalog
rgb-pgs.dat 378 6098245 PGS-giants (2420898 stars, with 75679 very
metal-poor candidates and 267 beyond 40kpc)
catalog
--------------------------------------------------------------------------------
See also:
I/354 : StarHorse2, Gaia EDR3 photo-astrometric distances
(Anders+, 2022)
J/A+A/692/A115 : Pristine survey DR1 (Martin+, 2024)
Byte-by-byte Description of file: rgb-pdr1.dat rgb-pgs.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaDR3 Gaia DR3 source (source_id)
21- 40 E20.16 deg RAdeg Gaia DR3 right ascension (ICRS)
at Ep=2016.0 (ra)
42- 63 E22.17 deg DEdeg Gaia DR3 declination (ICRS) at Ep=2016.0(dec)
65- 86 E22.17 mas plx Gaia DR3 offset-corrected parallax (parallax)
88-107 F20.18 mas e_plx Offset-corrected uncertainty on the Gaia DR3
offset-corrected parallax (parallax_error)
109-130 E22.17 mas/yr pmRA Gaia DR3 proper motion in RA direction (pmra)
132-143 F12.10 mas/yr e_pmRA Uncertainty on Gaia DR3 proper motion
in RA direction (pmra_error)
145-166 E22.17 mas/yr pmDE Gaia DR3 proper motion in DE direction (pmdec)
168-179 F12.10 mas/yr e_pmDE Uncertainty on Gaia DR3 proper motion
in DE direction (pmdec_error)
181-199 F19.16 mag G0mag De-reddened Gaia DR3 G magnitude (G_0)
201-219 F19.16 mag BP0mag De-reddened Gaia DR3 BP magnitude (BP_0)
221-239 F19.16 mag RP0mag De-reddened Gaia DR3 RP magnitude (RP_0)
241-262 F22.18 kpc Dist Photometric distance inferrer in this work
(phot_dist)
264-285 F22.19 kpc e_Dist Uncertainty on photometric distance inferrer
in this work (photdistunc)
287-307 E21.17 km/s Vlos ?=-9999 Radial velocity cross-matched with
spectroscopic surveys (v_los)
309-333 F25.18 km/s e_Vlos ?=-9999 Uncertainty in radial velocity
cross-matched with spectroscopic surveys
(vlosunc)
335-356 E22.17 --- [Fe/H] Photometric metallicity derived in the
PDR1/PGCS catalogues (FeH_phot)
358-378 E21.19 --- e_[Fe/H] Measurement uncertainty on the photometric
metallicity derived in the PDR1/PGCS
catalogues (FeHphotunc)
--------------------------------------------------------------------------------
Acknowledgements:
Akshara Viswanathan, astroakshara97(at)gmail.com
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(End) Patricia Vannier [CDS] 02-Jan-2026