Unveiling the small-scale web around galaxies with miniJPAS and DESI

¹ Max-Planck Institute for Astrophysics Karl-Schwarzschild-Str. 1 D-85741 Garching, Germany
² Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa Chiba 277-8583, Japan
³ Donostia International Physics Center (DIPC) Paseo Manuel de Lardizabal 4 20018 Donostia-San Sebastian, Spain
⁴ IKERBASQUE, Basque Foundation for Science E-48013 Bilbao, Spain
⁵ Hamburger Sternwarte, Universität Hamburg Gojenbergsweg 112 D-21029 Hamburg, Germany
⁶ Instituto de Astrofísica de Andalucía (IAA-CSIC) P.O.ox 3004 18080 Granada, Spain
⁷ Tartu Observatory, University of Tartu Observatooriumi 1 61602 Tõravere, Estonia
⁸ Estonian Academy of Sciences Kohtu 6 10130 Tallinn, Estonia
⁹ Departamento de Física Matemática, Instituto de Física, Universidade de São Paulo, Rua do Matão 1371 CEP 05508-090 São Paulo, Brazil
¹⁰ Observatori Astronòmic de la Universitat de València, Ed. Instituts d’Investigació, Parc Científic. C/ Catedrático José Beltrán, n2 46980 Paterna Valencia, Spain
¹¹ Departament d’Astronomia i Astrofísica, Universitat de València 46100 Burjassot, Spain
¹² Departamento de Física, Universidade Federal do Espírito Santo 29075-910 Vitória ES, Brazil
¹³ INAF – Osservatorio Astronomico di Trieste via Tiepolo 11 34131 Trieste, Italy
¹⁴ IFPU – Institute for Fundamental Physics of the Universe via Beirut 2 34151 Trieste, Italy
¹⁵ Observatório Nacional, Rua General José Cristino, 77 São Cristóvão 20921-400 Rio de Janeiro RJ, Brazil
¹⁶ Centro de Estudios de Física del Cosmos de Aragón (CEFCA) Plaza San Juan 1 E–44001 Teruel, Spain
¹⁷ Unidad Asociada CEFCA-IAA, CEFCA, Unidad Asociada al CSIC por el IAA Plaza San Juan 1 44001 Teruel, Spain
¹⁸ Instituto de Astrofísica de Canarias (IAC) C. Vía Láctea 38205 La Laguna Santa Cruz de Tenerife, Spain
¹⁹ Universidad de La Laguna, Avda Francisco Sánchez E-38206 San Cristóbal de La Laguna Tenerife, Spain
²⁰ Universidade de São Paulo, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Rua do Matão 1226 05508-090 São Paulo SP, Brazil
²¹ Instruments4 4121 Pembury Place La Canada Flintridge CA 91011, USA

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Received: 19 June 2025
Accepted: 3 December 2025

Abstract

We present the first statistical observational study detecting filaments in the immediate surroundings of galaxies, i.e. the local web of galaxies. Simulations predict that cold gas, the fuel for star formation, is channeled through filamentary structures into galaxies. Yet, direct observational evidence for this process has been limited by the challenge of mapping the cosmic web at small scales. Using miniJPAS spectro-photometric data combined with spectroscopic DESI redshifts when available, we constructed a high-density observational galaxy sample spanning 0.2 < z < 0.8. Local filaments are detected within a 3 Mpc physical radius of each galaxy with stellar mass M_★ > 10¹⁰ M_⊙ using all nearby galaxies as tracers, combined with a probabilistic adaptation of the DisPerSE algorithm designed to overcome limitations due to photometric redshift uncertainties. Our methodology was tested and validated using mock catalogues built with random forest models applied to a simulated lightcone. Besides recovering the expected increase in galaxy connectivity (defined as the number of filaments attached to a galaxy) with stellar mass, we show that our connectivity measurements agree with 3D reference estimates from the mock galaxies. Thanks to these filament reconstructions, we explore the relation between small-scale connectivity and galaxy star formation rate, finding a mild positive trend which needs to be confirmed by follow-up studies with larger sample sizes. We propose galaxy connectivity to local filaments as a powerful and physically motivated metric of environment, offering new insights into the role of cosmic structure in galaxy evolution.