Estimating the completeness of the QUBRICS Survey with 3501 QSO redshifts from Gaia DR3 spectra

Abstract

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 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. We aim 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 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 its dataset as unclassified objects. The PRF correctly identified as candidates 46 (66%) of the 69 QSOs with z>2.5 present in its 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.

14 pages, 9 figures, accepted for publication in Astronomy & Astrophysics; abstract abridged

References in corpus (26)

• Gaia Data Release 3: Summary of the content and survey properties
• Initial Performance of the NEOWISE Reactivation Mission
• Euclid. I. Overview of the Euclid mission
• The Sloan Digital Sky Survey Quasar Catalog: Sixteenth Data Release
• The Early Data Release of the Dark Energy Spectroscopic Instrument
• The Dark Energy Survey Data Release 2
• The CatWISE2020 Catalog
• Hydrogen reionisation ends by $z=5.3$: Lyman-$\alpha$ optical depth measured by the XQR-30 sample
• Cosmic dynamics in the era of Extremely Large Telescopes
• The High Latitude Spectroscopic Survey on the Nancy Grace Roman Space Telescope
• Internal calibration of Gaia BP/RP low-resolution spectra
• Fundamental physics with ESPRESSO: Precise limit on variations in the fine-structure constant towards the bright quasar HE 0515$-$4414
• The Extremely Luminous Quasar Survey in the Sloan Digital Sky Survey footprint. III. The South Galactic Cap Sample and the Quasar Luminosity Function at Cosmic Noon
• DESI z >~ 5 Quasar Survey. I. A First Sample of 400 New Quasars at z ~ 4.7-6.6
• The Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) Quasar Survey: Quasar Properties from Data Release Six to Nine
• The space density of ultra-luminous QSOs at the end of reionization epoch by the QUBRICS Survey and the AGN contribution to the hydrogen ionizing background
• The spectroscopic follow-up of the QUBRICS bright quasar survey
• UNCOVERing the contribution of black holes to reionization in the JWST era
• The Luminosity Function of bright QSOs at z~4 and implications for the cosmic ionizing background
• Ultra-luminous quasars at redshift $z>4.5$ from SkyMapper
• Spectroscopy of QUBRICS quasar candidates: 1672 new redshifts and a Golden Sample for the Sandage Test of the Redshift Drift
• The Probabilistic Random Forest applied to the selection of quasar candidates in the QUBRICS Survey
• Eddington accreting Black Holes in the Epoch of Reionization
• The ESPRESSO Redshift Drift Experiment I -- High-resolution spectra of the Lyman-$\alpha$ forest of QSO J052915.80-435152.0
• The probabilistic random forest applied to the QUBRICS survey: improving the selection of high-redshift quasars with synthetic data
• A comparison of cosmological models with high-redshift quasars