Star-forming compact groups: Tracing the early evolutionary stages of compact group environments

¹ Departamento de Astronomía, Universidad de La Serena Av. Raúl Bitrán 1305 La Serena, Chile
² Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo, Cidade Universitŕia CEP:05508-900 São Paulo SP, Brazil
³ Departamento de Tecnologías Industriales, Facultad de Ingeniería, Universidad de Talca Los Niches km 1 Curicó, Chile
⁴ Facultad de Ciencias Exactas, Institute of Astrophysics, Universidad Andrés Bello, Sede Concepción Talcahuano 7100 Concepción 4260000, Chile
⁵ Departamento de Física, Universidad Técnica Federico Santa María Avenida España 1600 Valparaíso, Chile
⁶ Instituto de Astrofísica de La Plata, CONICET-UNLP Paseo del Bosque s/n B1900FWA La Plata, Argentina
⁷ Observatório do Valongo/UFRJ, Ladeira do Pedro Antônio 43 Centro Rio de Janeiro RJ 20080-090, Brazil
⁸ Institute of Physics, Federal University of Rio de Janeiro Av. Athos da Silveira Ramos 149 Rio de Janeiro RJ 21941909, Brazil
⁹ Observatório Nacional, Rua General José Cristino, 77 São Cristóvão 20921-400 Rio de Janeiro RJ, Brazil
¹⁰ Departamento de Física, Universidade Federal de Santa Catarina Florianópolis SC 88040-900, Brazil
¹¹ NOAO 950 North Cherry Ave. Tucson AZ 85719, United States
¹² The Observatories of the Carnegie Institution for Science 813 Santa Barbara St Pasadena CA 91101, USA

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

Received: 25 July 2025
Accepted: 13 January 2026

Abstract

Context. In the context of pre-processing – a scenario where galaxies quench their star formation within substructures before falling into clusters – we investigate the impact of environment on the physical and morphological properties of galaxies in compact groups (CGs), focusing specifically on a sample of star-forming CGs (SFCGs).

Aims. Our aim is to characterize the physical and morphological properties of galaxies in SFCGs – analogs to the Blue Infalling Group – and understand how the environment influences their evolution.

Methods. We used photometric techniques to derive stellar masses and star formation rates (SFRs). Morphological parameters were extracted from DECaLS images, and we obtained parametric properties such as the Sérsic index (n) and effective radius (R_e) using GALFITM and non-parametric indices – including Gini, M₂₀, and asymmetry – from the same data. These indicators allowed us to classify galaxies into E/S0/Sa, Sb/Sc/Ir, and merger types. All measurements were compared to a control sample of field galaxies to assess environmental effects.

Results. We find no significant differences in n and R_e between SFCG and field galaxies, in contrast to results for other CG samples. However, SFCG galaxies exhibit higher specific SFRs than field counterparts. About 16% of SFCG galaxies show merger features and elevated asymmetry. These mergers also present enhanced SFRs compared to both other SFCG types and the field.

Conclusions. We propose that SFCGs represent an earlier evolutionary phase of CGs, supported by their lower velocity dispersions and moderate crossing times in addition to the observed SFR enhancement and absence of pronounced morphological transformation. Galaxy mergers in this phase appear to enhance, rather than suppress, star formation.