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

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, M 20 , 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.