Targeting cluster galaxies for the 4MOST CHANCES Low-z sub-survey with photometric redshifts

¹ Departamento de Astronomía, Universidad de La Serena Avda. Raúl Bitrán 1305 La Serena, Chile
² Departamento de Física, Universidad Técnica Federico Santa María Avenida España 1680 Valparaíso, Chile
³ Instituto de Astronomía y Ciencias Planetarias (INCT), Universidad de Atacama Copayapu 485 Copiapó, Chile
⁴ Millennium Nucleus for Galaxies (MINGAL) Valparaíso, Chile
⁵ Centro Brasileiro de Pesquisas Físicas Rua Dr. Xavier Sigaud 150 22290-180 Rio de Janeiro RJ, Brazil
⁶ Departamento de Astronomia, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão 1226, Cidade Universitária São Paulo 05508-090, Brazil
⁷ Institute of Astronomy, University of Cambridge Madingley Road Cambridge CB3 0HA, United Kingdom
⁸ Institute of Astrophysics, Facultad de Ciencias Exactas, Universidad Andrés Bello Sede Concepción Talcahuano, Chile
⁹ Department of Physics, University of Helsinki Gustaf Hällströminkatu 2 00560 Helsinki, Finland
¹⁰ Instituto de Astrofísica de La Plata, CONICET-UNLP Paseo del Bosque s/n B1900FWA La Plata, Argentina
¹¹ Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata Paseo del Bosque s/n B1900FWA La Plata, Argentina
¹² INAF – Osservatorio Astronomico di Capodimonte Salita Moiariello 16 80131 Napoli, Italy
¹³ Instituto de Física, Pontificia Universidad Católica de Valparaíso Casilla 4059 Valparaíso, Chile
¹⁴ Departamento de Física Teórica y del Cosmos, Edificio Mecenas, Campus Fuentenueva, Universidad de Granada E-18071 Granada, Spain
¹⁵ Instituto Universitario Carlos I de Física Teórica y Computacional, Universidad de Granada 18071 Granada, Spain
¹⁶ Instituto de Física y Astronomía, Universidad de Valparaíso Avda. Gran Bretaña 1111 Valparaíso, Chile
¹⁷ School of Physics & Astronomy, University of Nottingham Nottingham NG7 2RD, UK
¹⁸ Valongo Observatory, Federal University of Rio de Janeiro, Ladeira do Pedro Antônio 43 Saúde CEP 20080-090 Rio de Janeiro RJ, Brazil
¹⁹ Departamento de Astronomía, Universidad de Chile Casilla 36-D Santiago, Chile
²⁰ School of Physics and Astronomy, University of Birmingham Birmingham B15 2TT, UK
²¹ Departamento de Física y Astronomía, Instituto de Astrofísica, Universidad Andres Bello Fernandez Concha 700 Las Condes Santiago 7591538, Chile
²² INAF-Osservatorio Astronomico di Padova Vicolo dell’Osservatorio 5 35136 Padova, Italy
²³ European Southern Observatory, Science Operations Alonso de Cordova 3107 Vitacura 19001 Santiago, Chile
²⁴ Cerro Tololo Inter-American Observatory, NSF’s National Optical-Infrared Astronomy Research Laboratory Casilla 603 La Serena, Chile
²⁵ Instituto Nacional de Pesquisas Espaciais (INPE/MCTI), Av. dos Astronautas 1758 São José dos Campos SP, Brazil
²⁶ Center for Theoretical Physics, Polish Academy of Sciences al. Lotników 32/46 02-668 Warsaw, Poland
²⁷ Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS Beijing 100101, China
²⁸ Key Laboratory of Optical Astronomy, NAOC street20A Datun Road Chaoyang District Beijing 100101, China
²⁹ Laboratório Nacional de Astrofísica (LNA), Rua dos Estados Unidos 154, Bairro das Nações 37504-364 Itajubá MG, Brazil
³⁰ Universidade Federal de Santa Catarina, Campus Universitário Reitor João David Ferreira Lima Florianópolis 88040-900, Brazil
³¹ Observatório Nacional / MCTIC Rua General José Cristino 77 Rio de Janeiro RJ 20921-400, Brazil
³² Departamento de Física Matemática, Instituto de Física, Universidade de São Paulo, SP Rua do Matão 1371 São Paulo, Brazil
³³ Escola Politecnica, Universidade de São Paulo, Av. Prof. Luciano Gualberto, travessa do politecnico 380 São Paulo 05508-010, Brazil
³⁴ Rubin Observatory Project Office 950 N. Cherry Ave Tucson 85719, USA
³⁵ Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University Grudziadzka 5 PL-87-100 Toruń, Poland
³⁶ Univ. Lyon1, Ens de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon (CRAL) UMR5574 F-69230 Saint-Genis-Laval, France
³⁷ Universidade do Vale do Paraíba, Av. Shishima Hifumi 2911 São José dos Campos 12244-000 SP, Brazil
³⁸ Universidade Estadual de Feira de Santana, Departamento de Física Feira de Santana BA 44.036-900, Brazil
³⁹ The Observatories of the Carnegie Institution for Science 813 Santa Barbara St Pasadena CA 91101, USA

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Received: 8 August 2025
Accepted: 12 October 2025

Abstract

Context. The evolution of galaxies is shaped by both internal processes and their external environments. Galaxy clusters and their surroundings provide ideal laboratories to study these effects, particularly with respect to mechanisms such as quenching and morphological transformation. The Chilean Cluster galaxy Evolution Survey (CHANCES) Low-z sub-survey is part of the CHileAN Cluster galaxy Evolution Survey, a 4MOST community survey designed to uncover the relationship between the formation and evolution of galaxies and hierarchical structure formation as it happens, through deep and wide multi-object spectroscopy.

Aims. We present the target selection strategy followed to select galaxy cluster candidate members for the CHANCES Low-z sub-survey. The selection was focussed in and around 50 clusters and two superclusters at z < 0.07, out to (5 × R₂₀₀) and down to m_r = 20.4.

Methods. Combining public photometric redshift estimates from the DESI Legacy Imaging Survey and T80S/S-PLUS iDR5 with custom photometric redshifts, we were able to identify likely galaxy cluster candidate members, whose photometric redshifts were consistent with being located at the known redshift of the cluster. We measured the average deviations of their photometric redshifts with respect to the spectroscopic redshift measurements, σ_NMAD. We tested various selection parameters to maximise completeness, while maintaining purity.

Results. We successfully compiled our CHANCES-low-redshift catalogues, split into three different sub-surveys: Low-z bright (m_r < 18.5), Low-z faint (18.5 ≤ m_r < 20.4), and Low-z faint supplementary. To do so, we selected ≳500 000 galaxy cluster candidate members and included confirmed spectroscopic galaxy cluster members, from which we expect to obtain 4MOST low-resolution (R ∼ 6500) spectra for ∼320 000 galaxies.

Conclusions. The CHANCES Low-z target catalogues form a statistically robust sample for spectroscopic follow-up, enabling studies of galaxy evolution and environmental effects in nearby cluster and supercluster environments.