The S-PLUS Fornax Project (S+FP): An extragalactic catalog covering ∼5 virial radii around NGC1399 with galaxy properties

¹ Instituto de Astrofísica de La Plata, UNLP-CONICET, Paseo del Bosque s/n, La Plata, B1900FWA, Argentina
² Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, La Plata, B1900FWA, Argentina
³ Departamento de Astronomia, Instituto de Astronomia, Geofísica e Ciências Atmosféricas da USP, Cidade Universitária, 05508-090 São Paulo, SP, Brazil
⁴ Institute of Astrophysics, Facultad de Ciencias Exactas, Universidad Andrés Bello, Sede Concepción, Talcahuano, Chile
⁵ Departamento de Tecnologías Industriales, Facultad de Ingeniería, Universidad de Talca, Los Niches km 1, Curicó, Chile
⁶ International Gemini Observatory/NSF’s National Optical-Infrared Research Laboratory, Casilla 603, La Serena, Chile
⁷ Universidade do Vale do Paraíba, Av. Shishima Hifumi, 2911, São José dos Campos SP 12244-000, Brazil
⁸ Valongo Observatory, Federal University of Rio de Janeiro, Ladeira Pedro Antonio 43, Saude Rio de Janeiro RJ 20080-090, Brazil
⁹ Departamento de Astronomía, Universidad de La Serena, Av. J. Cisternas 1200 N, 1720236 La Serena, Chile
¹⁰ Observatório Nacional, Rua General José Cristino, 77, São Cristóvão, 20921-400 Rio de Janeiro RJ, Brazil
¹¹ Departamento de Física, Universidad Técnica Federico Santa María, Avenida España 1680, Valparaíso, Chile
¹² Millennium Nucleus for Galaxies (MINGAL), Santiago, Chile
¹³ Laboratório Nacional de Astrofísica, Rua Estados Unidos 154, Itajubá 37504-364 MG, Brazil
¹⁴ GMTO Corporation 465 N. Halstead Street, Suite 250 Pasadena, CA 91107, USA
¹⁵ Rubin Observatory Project Office, 950 N. Cherry Ave., Tucson, AZ 85719, USA
¹⁶ Departamento de Física – CFM – Universidade Federal de Santa Catarina, PO BOx 476, 88040-900 Florianópolis, SC, Brazil

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 15 November 2025
Accepted: 28 January 2026

Abstract

Context. Observational extragalactic catalogs over wide sky areas are essential for uncovering the large-scale structure of the Universe. They allow, among other things, cosmological studies and density analyses that impose strong constraints on models of galaxy formation and evolution.

Aims. By taking advantage of the wide field images and the 12 optical bands of the Southern Photometric Local Universe Survey (S-PLUS), we aim to provide a catalog of galaxies located, in projection, toward the Fornax galaxy cluster, within ∼ 5 virial radii in right ascension (RA) and ∼3 virial radii in declination (Dec) around NGC 1399, the dominant galaxy of the cluster. Such a catalog will allow unprecedented large-scale structure studies in that sky region.

Methods. We developed supervised deep-learning algorithms, utilizing neural networks complemented by dimensionality-reduction techniques, to classify and separate spurious objects, stars and galaxies in a photometric catalog previously built for the S-PLUS Fornax Project (S+FP). That catalog was built using a combination of SExtractor configurations optimized for galaxy detection and characterization.

Results. A catalog of 119 580 galaxies was obtained in the direction of the Fornax cluster containing photometric information in the 12 optical bands of S-PLUS complemented with GALEX (UV), VHS-VISTA (NIR), and AllWISE (MIR) data. We estimate photometric redshifts (σ_NMAD ∼ 0.0219) with a lower limit of z_lim ∼ 0.03. Stellar masses, star formation rates (SFRs), and D4000_N index estimates were obtained through a machine-learning approach, by matching S-PLUS photometric data to SDSS spectroscopic data. The completeness of the catalog (72%) was calculated by comparing it with mock catalogs.

Conclusions. Taking into account our z_lim, we were able to identify 119 230 background galaxies and to find 350 candidates to be Fornax members or infalling galaxies, which were not included in our compilation of 1005 galaxies previously reported in the literature. We were also able to classify the galaxies in our catalog as quiescent (43%), star forming (39%), and transition (18%) galaxies. In addition, 181 emission line galaxy (ELG) candidates were identified using the filter J0660. The spatial distribution of the galaxies in our catalog shows projected overdensities that match 158 background clusters identified by eROSITA. This confirms the robustness of our catalog in tracing real structures. In that context, we expect the extragalactic catalog of the S+FP to allow us to better understand the large-scale structure in the direction of the Fornax cluster and to identify the substructures that are feeding Fornax.