Photometric redshifts for active galactic nuclei with LePHARE for the Vera C. Rubin Observatory
Abstract
Active Galactic Nuclei (AGN) play a crucial role in galaxy evolution, but they are a minority of extragalactic sources with diverse Spectral Energy Distributions (SEDs), which depend on their means of selection. Upcoming large-scale surveys such as LSST will identify many AGN, but analysis tools are not optimized for them. The limited number of photometric bands in these surveys impacts the calculation of photometric redshifts for AGN, which are essential for scientific advancement. We use LePHARE to demonstrate the impact that a limited number of bands and erroneous assumptions have on the determination of the photometric redshifts of AGN. We conduct tests on six AGN samples selected using X-ray, radio, infrared, variability, color, and spectroscopic criteria in the COSMOS field, using photometry from HSC-CLAUDS, which is closest in depth and wavelength coverage to LSST. We present the LSST pipeline for LePHARE within the Redshift Assessment Infrastructure Layers (RAIL), facilitating comparison between SED fitting and machine learning algorithms. AGN that appear as point-like sources in optical data will be assigned highly unreliable photometric redshifts if they are processed using galaxy templates. Additionally, shallow all-sky surveys (like eROSITA, WISE, and ZTF) miss many AGN. As a result, these "hidden" AGN are often misidentified as galaxies in public survey data, leading to incorrect photometric redshift. We provide the configurations that are suggested for each type of AGN alongside measures of expected performance as a function of redshift, magnitude, and selection. To facilitate studies with a panchromatic view of AGN, we also release photometric redshifts and posterior distributions for all AGN sources identified in the COSMOS field using the six criteria, based on 28-band photometry.
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BibTeX
@misc{shirley2026photometric,
title = {{Photometric redshifts for active galactic nuclei with LePHARE for the Vera C. Rubin Observatory}},
author = {R. Shirley and M. Salvato and J. Cohen-Tanugi and O. Ilbert and S. Arnouts and R. Ansari and R. Assef and M. Banerji and A. Bongiorno and W. N. Brandt and J. Buchner and J. Comparat and D. Ilić and A. Kovačević and J. Kubica and B. Laloux and O. Lynn and A. Malz and L. Marchetti and C. Mazzucchelli and T. Mkrtchyan and K. Nandra and D. Oldag and C. Ricci and W. Roster and E. Saremi and S. Satheesh-Sheeba and T. Tasnim. Ananna and M. J. Temple and M. Vaccari and A. Viitanen and C. Wolf and Z. Yu and T. Zhang},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2608.30494},
eprint = {2608.30494},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.30494},
}
RIS
TY - UNPB
TI - Photometric redshifts for active galactic nuclei with LePHARE for the Vera C. Rubin Observatory
AU - R. Shirley
AU - M. Salvato
AU - J. Cohen-Tanugi
AU - O. Ilbert
AU - S. Arnouts
AU - R. Ansari
AU - R. Assef
AU - M. Banerji
AU - A. Bongiorno
AU - W. N. Brandt
AU - J. Buchner
AU - J. Comparat
AU - D. Ilić
AU - A. Kovačević
AU - J. Kubica
AU - B. Laloux
AU - O. Lynn
AU - A. Malz
AU - L. Marchetti
AU - C. Mazzucchelli
AU - T. Mkrtchyan
AU - K. Nandra
AU - D. Oldag
AU - C. Ricci
AU - W. Roster
AU - E. Saremi
AU - S. Satheesh-Sheeba
AU - T. Tasnim. Ananna
AU - M. J. Temple
AU - M. Vaccari
AU - A. Viitanen
AU - C. Wolf
AU - Z. Yu
AU - T. Zhang
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2608.30494
UR - https://arxiv.org/abs/2608.30494
AB - Active Galactic Nuclei (AGN) play a crucial role in galaxy evolution, but they are a minority of extragalactic sources with diverse Spectral Energy Distributions (SEDs), which depend on their means of selection. Upcoming large-scale surveys such as LSST will identify many AGN, but analysis tools are not optimized for them. The limited number of photometric bands in these surveys impacts the calculation of photometric redshifts for AGN, which are essential for scientific advancement. We use LePHARE to demonstrate the impact that a limited number of bands and erroneous assumptions have on the determination of the photometric redshifts of AGN. We conduct tests on six AGN samples selected using X-ray, radio, infrared, variability, color, and spectroscopic criteria in the COSMOS field, using photometry from HSC-CLAUDS, which is closest in depth and wavelength coverage to LSST. We present the LSST pipeline for LePHARE within the Redshift Assessment Infrastructure Layers (RAIL), facilitating comparison between SED fitting and machine learning algorithms. AGN that appear as point-like sources in optical data will be assigned highly unreliable photometric redshifts if they are processed using galaxy templates. Additionally, shallow all-sky surveys (like eROSITA, WISE, and ZTF) miss many AGN. As a result, these "hidden" AGN are often misidentified as galaxies in public survey data, leading to incorrect photometric redshift. We provide the configurations that are suggested for each type of AGN alongside measures of expected performance as a function of redshift, magnitude, and selection. To facilitate studies with a panchromatic view of AGN, we also release photometric redshifts and posterior distributions for all AGN sources identified in the COSMOS field using the six criteria, based on 28-band photometry.
ER -