Cluster-green galaxy correlations: Where do these galaxies live?

¹ Instituto de Astronomía Teórica y Experimental, CONICET – UNC, Laprida 854, X5000BGR, Córdoba, Argentina
² Facultad de Matemática, Astronomía, Física y Computación, Universidad Nacional de Córdoba, Av. Medina Allende s/n, X5000HUA, Córdoba, Argentina
³ Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, X5000BGR, Córdoba, Argentina

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

Received: 24 July 2025
Accepted: 20 April 2026

Abstract

Context. Green valley (GV) galaxies are thought to represent a transitional population between star-forming and quiescent systems. However, their spatial distribution relative to galaxy systems, such as galaxy groups and clusters, remains unclear, particularly in relation to the large-scale environmental influence on galaxy quenching.

Aims. We aim to determine whether GV galaxies preferentially inhabit specific environments within galaxy systems, and to explore the physical nature of their location on the outskirts of massive haloes.

Methods. We analysed the spatial distribution of GV galaxies using the cluster–galaxy cross-correlation function, based on two datasets: the hydrodynamical simulation Illustris TNG300-1 and observational data from the Sloan Digital Sky Survey (SDSS DR18), cross-matched with the MPA–JHU DR7 catalogue. Galaxy systems with log(M₂₀₀/M_⊙)≥13.5 are used as cluster centres, while galaxies classified as blue, green, or red, based on their location in the (u − r) versus stellar mass diagram, serve as tracers for the correlation analysis.

Results. In TNG, GV galaxies show an increasing relative fraction with cluster-centric distance, peaking on the outskirts, particularly for low-mass galaxies and haloes. In some cases, the GV fraction exceeds that of red galaxies. SDSS data reveal qualitatively similar, but weaker trends, with the GV fraction remaining below that of red galaxies at all scales. Most GV galaxies on the outskirts are satellites bound to the central FoF group, consistent with a backsplash or infall origin. Mock catalogues built from TNG and matched to SDSS selection functions reproduce the observational signal, indicating that projection effects drive the differences between datasets.

Conclusions. GV galaxies preferentially reside on the outskirts of galaxy systems as satellites bound to the central halo, supporting a scenario in which they are transitioning objects influenced by environmental quenching.