Measuring the Probabilistic Photometric Redshifts of X-ray Quasars Based on the Quantile Regression of Ensembles of Decision Trees

• Published in: Astronomy letters Vol. 44; no. 12; pp. 735 - 753
• Main Authors: Meshcheryakov, A. V., Glazkova, V. V., Gerasimov, S. V., Mashechkin, I. V.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.12.2018; Springer Nature B.V
• Subjects: Algorithms; Astronomy; Astrophysics and Astroparticles; Confidence intervals; Decision trees; Distribution functions; Empirical analysis; Machine learning; Observations and Techniques; Outliers (statistics); Photometry; Physics; Physics and Astronomy; Probability distribution; Probability distribution functions; Quasars; Red shift; Regression analysis; Sky surveys (astronomy); Statistical analysis; ART-XC; XMM-Newton; ROSAT; GALEX; 2MASS; SRG; random forest; machine learning; WISE; FIRST; photometric redshifts; eRosita; gradient boosting; decision trees; SDSS; quantile regression; UKIDSS; quasars
• ISSN: 1063-7737; 1562-6873
• DOI: 10.1134/S1063773718120058

We present empirical machine learning algorithms for measuring the probabilistic photometric redshifts (photo-z) of X-ray quasars based on the quantile regression of ensembles of decision trees. Relying on the data of present-day photometric sky surveys (e.g., SDSS, GALEX, WISE, UKIDSS, 2MASS, FIRST), the proposed methods allow one to make high-quality photo-z point predictions for extragalactic objects, to estimate the confidence intervals, and to reconstruct the full probability distribution functions for all predictions. The quality of photo-z predictions has been tested on samples of X-ray quasars from the 1RASS and 3XMM DR7 surveys, which have spectroscopic redshift measurements in the SDSS DR14Q catalog. The proposed approaches have shown the following accuracy (the metrics are the normalized median absolute deviation σNMAD and the percentage of outliers n >0.15 ): σ NMAD , n >0.15 = 0.043, 12% (SDSS + WISE), 0.037, 8% (SDSS + WISE + GALEX) and 0.032, 8.6% (SDSS + WISE + GALEX + UKIDSS) on the RASS sample; σ NMAD , n >0.15 = 0.054, 13% (SDSS + WISE), 0.045, 7.6% (SDSS + WISE + GALEX), and 0.037, 6.6% (SDSS + WISE + GALEX + UKIDSS) on the 3XMM sample. The presented photo-z algorithms will become an important tool for analyzing the multi-wavelength data on X-ray quasars in the forthcoming Spectrum–Roentgen–Gamma sky survey.