ODIN: Using multiplicity of Lyman-alpha emitters to assess star formation activity in dark matter halos

¹ Instituto de Astronomía Teórica y Experimental (IATE), CONICET-UNC Laprida 854 X500BGR Córdoba, Argentina
² Facultad de Matemática, Astronomía, Física y Computación, Universidad Nacional de Córdoba, Bvd. Medina Allende s/n Ciudad Universitaria X5000HU Córdoba, Argentina
³ Observatorio Astronómico de Córdoba, Universidad Nacional de Córdoba Laprida 854 X5000BGR Córdoba, Argentina
⁴ Department of Physics and Astronomy, Rutgers, the State University of New Jersey Piscataway NJ 08854, USA
⁵ Universidad Andres Bello, Facultad de Ciencias Exactas, Departamento de Fisica y Astronomia, Instituto de Astrofisica, Fernandez Concha 700 Las Condes Santiago RM, Chile
⁶ Department of Physics and Astronomy, Purdue University 525 Northwestern Avenue West Lafayette IN 47906, USA
⁷ Korea Institute for Advanced Study 85 Hoegi-ro Dongdaemun-gu Seoul 02455, Republic of Korea
⁸ Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro Yuseong-gu Daejeon 34055, Republic of Korea
⁹ Department of Astronomy and Astrophysics, The Pennsylvania State University University Park PA 16803, USA
¹⁰ Institute for Gravitation and the Cosmos, The Pennsylvania State University University Park PA 16803, USA
¹¹ Millennium Nucleus for Galaxies (MINGAL), Chile
¹² Astronomy Program, Department of Physics and Astronomy, Seoul National University 1 Gwanak-ro Gwanak-gu Seoul 08826, Republic of Korea
¹³ SNU Astronomy Research Center, Seoul National University 1 Gwanak-ro Gwanak-gu Seoul 08826, Republic of Korea
¹⁴ Australian Astronomical Optics – Macquarie University 105 Delhi Road North Ryde NSW 2113, Australia
¹⁵ Escuela de Ingeniería, Universidad Central de Chile, Avenida Francisco de Aguirre 0405 171-0614 La Serena Coquimbo, Chile
¹⁶ Steward Observatory, University of Arizona 933 North Cherry Avenue Tucson AZ 85721, USA

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Received: 2 September 2025
Accepted: 22 November 2025

Abstract

Aims. We investigate if systems of multiple Lyman-alpha emitters (LAEs) can serve as a proxy for dark matter halo mass, assess how their radiative properties relate to the underlying halo conditions, and explore the physics of star formation activity in LAEs and its relation to possible physically related companions.

Methods. We used data from the One-hundred-deg² DECam Imaging in Narrowbands (ODIN) survey, which targets LAEs in three narrow redshift slices. We identified physically associated LAE multiples in the COSMOS field at z = 2.4, z = 3.1, and z = 4.5, and we used a mock catalog from the IllustrisTNG100 simulation to assess the completeness and contamination affecting the resulting sample of LAE multiples. We then studied their statistical and radiative properties as a function of multiplicity, for which we adopted the term “multiplicity” to refer to the number of physically associated LAEs.

Results. We find a strong correlation between LAE multiplicity and host halo mass in the mocks, with higher multiplicity systems preferentially occupying more massive halos. In both the ODIN and the mock sample, we find indications that the mean Lyα luminosity and UV magnitude of LAEs in multiples increase with multiplicity. The halo-wide LAE surface brightness densities in Lyα and UV increase with multiplicity, reflecting more compact and actively star-forming environments. The close agreement between the model and ODIN-COSMOS observations supports the validity of the Lyα emission model in capturing key physical processes in LAE environments. Finally, a subhalo-based perturbation-induced star formation model reproduces the minimum subhalo mass distribution in simulations at z = 2.4, suggesting that local perturbations–rather than the presence of LAE companions–drive star formation activity in these systems. For the higher redshift samples, neighbor perturbations do not seem to be the main driver that triggers star formation.