J/A+A/708/A363 The completeness of the QUBRICS Survey (Porru+, 2026)
Estimating the completeness of the QUBRICS survey with 3501 quasi-stellar object
redshifts from Gaia DR3 spectra.
Porru M., Cristiani S., Guarneri F., Calderone G., Grazian A., Boutsia K.,
Trost A., D'Odorico V., Cupani G., Marques C.M.J., Chiti Tegli F.,
Fontanot F.
<Astron. Astrophys. 708, A363 (2026)>
=2026A&A...708A.363P 2026A&A...708A.363P (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; QSOs ; Redshifts ; Optical
Keywords: methods: data analysis - methods: statistical -
astronomical databases: miscellaneous - surveys - quasars: general
Abstract:
Quasi-Stellar Objects (QSOs) are essential for investigating the
structure and evolution of the Universe. Historically, their
identification has been concentrated in the northern hemisphere,
primarily due to the sky coverage of major astronomical surveys. The
QUBRICS (QUasars as BRIght beacons for Cosmology in the Southern
hemisphere) survey, started in 2019 to address this asymmetry, has
identified more than 1300 new bright (i<19.5) high-redshift (2.5<z<6)
QSOs in the southern sky. This study aims to quantify, using an
independent QSO sample, the completeness and recall of the QUBRICS QSO
selection methods, based on XGB (eXtreme Gradient Boosting) and PRF
(Probabilistic Random Forest), since completeness is a fundamental
metric for ensuring the statistical robustness of QSO-based
cosmological investigations. A subset (G<18.25, |b|>25deg, negligible
parallax and proper motion) of Gaia DR3 sources with low-resolution
spectra was analyzed, obtaining a sample of 3501 QSOs.To determine how
many QSOs were correctly identified as candidates, we crossmatched
this independent sample with the datasets used for selection: 894 QSOs
with z>2.5 fell within the XGB dataset footprint, of which 152 were
unclassified and thus eligible for completeness testing. Similarly,
675 QSOs with z>2.5 were within the PRF dataset footprint, including
69 unclassified objects. The XGB correctly identified as candidates
136 (89%) of the 152 QSOs with z>2.5 present in the XGB dataset as
unclassified objects.The PRF correctly identified as candidates 46
(66%) of the 69 QSOs with z>2.5 present in the PRF dataset as
unclassified objects.These findings confirm the high efficiency of the
QUBRICS selection methods (recall=89%) and provide the completeness
estimate for spectroscopically confirmed QSOs (82%), necessary for
cosmological studies using QUBRICS data. This work also provides
reliable redshifts for 1223 new QSOs (median redshift z=2.1 and
magnitude G=17.8), that will help improve the performance of future
selections.
Description:
We present the entire sample of 3501 QSOs identified with our method
(table1.dat), with the spectroscopic redshift zQUG measured from the
Gaia DR3 spectra.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 68 3501 QSOs identified from Gaia DR3 spectra
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See also:
I/355 : Gaia DR3 Main Source catalog (Gaia Collaboration, 2022)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 I8 --- Qid QUBRICS unique identifier
10- 28 I19 --- GaiaDR3 Gaia DR3 unique source identifier
30- 31 I2 h RAh Gaia DR3 Right Ascension (ICRS) at Ep=2000
33- 34 I2 min RAm Gaia DR3 Right Ascension (ICRS) at Ep=2000
36- 40 F5.2 s RAs Gaia DR3 Right Ascension (ICRS) at Ep=2000
42 A1 --- DE- Gaia DR3 Declination (ICRS) at Ep=2000
43- 44 I2 deg DEd Gaia DR3 Declination (ICRS) at Ep=2000
46- 47 I2 arcmin DEm Gaia DR3 Declination (ICRS) at Ep=2000
49- 52 F4.1 arcsec DEs Gaia DR3 Declination (ICRS) at Ep=2000
54- 60 F7.4 mag Gmag Gaia DR3 G magnitude
62 I1 --- QOP Spectrum quality rating
64- 68 F5.3 --- zQUG Spectroscopic redshift
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Acknowledgements:
From Matteo Porru, matteo.porru(at)inaf.it
QUBRICS project team
License: CC-BY-4.0 [see https://spdx.org/licenses/]
(End) Patricia Vannier [CDS] 09-Mar-2026