The probabilistic random forest applied to the QUBRICS survey: improving the selection of high-redshift quasars with synthetic data

Abstract

Several recent works have focused on the search for bright, high-z quasars (QSOs) in the South. Among them, the QUasars as BRIght beacons for Cosmology in the Southern hemisphere (QUBRICS) survey has now delivered hundreds of new spectroscopically confirmed QSOs selected by means of machine learning algorithms. Building upon the results obtained by introducing the probabilistic random forest (PRF) for the QUBRICS selection, we explore in this work the feasibility of training the algorithm on synthetic data to improve the completeness in the higher redshift bins. We also compare the performances of the algorithm if colours are used as primary features instead of magnitudes. We generate synthetic data based on a composite QSO spectral energy distribution. We first train the PRF to identify QSOs among stars and galaxies, then separate high-z quasar from low-z contaminants. We apply the algorithm on an updated dataset, based on SkyMapper DR3, combined with Gaia eDR3, 2MASS and WISE magnitudes. We find that employing colours as features slightly improves the results with respect to the algorithm trained on magnitude data. Adding synthetic data to the training set provides significantly better results with respect to the PRF trained only on spectroscopically confirmed QSOs. We estimate, on a testing dataset, a completeness of ~86% and a contamination of ~36%. Finally, 207 PRF-selected candidates were observed: 149/207 turned out to be genuine QSOs with z > 2.5, 41 with z < 2.5, 3 galaxies and 14 stars. The result confirms the ability of the PRF to select high-z quasars in large datasets.

arXiv comment18 pages, 15 figures. Accepted for publication (MNRAS). Removed a source from the catalogue due to uncertain classification (a star, QID = 1016233)

References in corpus (37)

• Array Programming with NumPy
• Astropy: A Community Python Package for Astronomy
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• The 2dF Galaxy Redshift Survey: Spectra and redshifts
• Composite Quasar Spectra From the Sloan Digital Sky Survey
• Spectral Energy Distributions and Multiwavelength Selection of Type 1 Quasars
• The 6dF Galaxy Survey: Final Redshift Release (DR3) and Southern Large-Scale Structures
• Spectroscopic Target Selection in the Sloan Digital Sky Survey: The Quasar Sample
• An ultra-luminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30
• The Sloan Digital Sky Survey Quasar Catalog: Sixteenth Data Release
• An updated analytic model for the attenuation by the intergalactic medium
• Precision measures of the primordial abundance of deuterium
• Cosmic dynamics in the era of Extremely Large Telescopes
• Evolution of the AGN UV luminosity function from redshift 7.5
• Dusty Structure Around Type-I Active Galactic Nuclei: Clumpy Torus Narrow Line Region and Near-Nucleus Hot Dust
• Dark Energy Survey Year 3 Results: Photometric Data Set for Cosmology
• Probabilistic Random Forest: A machine learning algorithm for noisy datasets
• Mean Spectral Energy Distributions and Bolometric Corrections for Luminous Quasars
• On the relative Contribution of high-redshift Galaxies and Active Galactic Nuclei to Reionization
• The Rise of Active Galactic Nuclei in the GAlaxy Evolution and Assembly semi-analytic model
• Fundamental physics with ESPRESSO: Precise limit on variations in the fine-structure constant towards the bright quasar HE 0515$-$4414
• Discovery of the most metal-poor damped Lyman-alpha system
• A new era of fine structure constant measurements at high redshift
• 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
• Photometric selection and redshifts for quasars in the Kilo-Degree Survey Data Release 4
• Finding the brightest cosmic beacons in the Southern Hemisphere
• The spectroscopic follow-up of the QUBRICS bright quasar survey
• 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
• Random Forests as a viable method to select and discover high redshift quasars
• The Extremely Luminous Quasar Survey in the Pan-STARRS 1 Footprint (PS-ELQS)
• Ultra-luminous quasars at redshift $z>4.5$ from SkyMapper
• The Luminosity Function of bright QSOs at z~4 and implications for the cosmic ionizing background
• The Probabilistic Random Forest applied to the selection of quasar candidates in the QUBRICS Survey
• Broadband spectral energy distributions of SDSS-selected quasars and of their host galaxies: intense activity at the onset of AGN feedback
• Matched photometric catalogs of GALEX UV sources with Gaia DR2 and SDSS DR14 databases (GUVmatch)

Cited by in corpus (2)

• Spectroscopy of QUBRICS quasar candidates: 1672 new redshifts and a Golden Sample for the Sandage Test of the Redshift Drift
• Estimating the completeness of the QUBRICS Survey with 3501 QSO redshifts from Gaia DR3 spectra