CLAS+: A large catalog of Changing-Look AGN candidates selected through S-PLUS narrow-band photometry
Year: 2026
Type: preprint
Abstract: Changing-look active galactic nuclei (CLAGN) exhibit rapid spectral transitions on timescales of months to years, challenging standard AGN unification models and providing unique insight into accretion-disk variability and obscuration processes. Despite their scientific importance, systematic searches for CLAGN remain limited by the scarcity of multi-epoch spectroscopy and the difficulty of constructing large samples efficiently. We introduce CLAS+, a catalog constructed by comparing synthetic photometry derived from DESI DR1 and SDSS DR17 spectra with contemporaneous narrow-band imaging from the S-PLUS survey. Applying our pipeline to a parent sample of 98,139 quasars, we select high-confidence CLAGN candidates above a threshold of reduced chi-squared $χ_r^2 > 15$. We identify 3,554 strong CLAGN candidates, corresponding to 3.6\% of the parent sample. This selected fraction is conditional on the adopted criterion and should not be interpreted as an intrinsic CLAGN occurrence rate. Cross-matching with existing CLAGN compilations shows that CLAS+ identifies a large population of previously unreported high-priority candidates (3,481). Among the spectroscopic--photometric comparisons with reliable temporal classification, 40\% are classified as photometric turn-on, 41\% as intermediate, and 19\% as turn-off. We also find an apparent redshift dependence in the relative fractions, with photometric turn-on candidates becoming more common at higher redshifts within the CLAS+ selected sample. Therefore, narrow-band photometry provides a powerful and efficient alternative to purely spectroscopic searches for identifying CLAGN candidates at scale. CLAS+ substantially expands the known CLAGN candidate population and provides a valuable target list for future spectroscopic follow-up and time-domain studies with facilities such as Rubin/LSST.
Source: arXiv (Cornell University)
Institutions: Universidade de São Paulo, National Observatory, Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional de Córdoba, Instituto de Astronomía Teórica y Experimental, Argentine National Observatory, International Gemini Observatory, Universidad Andrés Bello, Universidade Federal de Santa Catarina
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, U.S. Department of Energy, National Aeronautics and Space Administration, Alfred P. Sloan Foundation, Princeton University, Ohio State University, University of Washington, Johns Hopkins University, University of Pittsburgh, Case Western Reserve University, Drexel University, Universität Basel, University of Portsmouth, New Mexico State University, Fundação de Amparo à Pesquisa do Estado de São Paulo, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Chinese Academy of Sciences, Conselho Nacional de Desenvolvimento Científico e Tecnológico, Max-Planck-Gesellschaft, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Financiadora de Estudos e Projetos, Universidade Federal de Santa Catarina, Universidade Federal de Sergipe, Agencia Nacional de Investigación y Desarrollo, Max-Planck-Institut für Astronomie, U.S. Naval Observatory, Fermilab, Los Alamos National Laboratory
OpenAlex ID: W7208730352