Star-forming compact groups: Tracing the early evolutionary stages of compact group environments
Ortiz-Gómez S., Torres-Flores S., Monachesi A., Montaguth G. P., Véliz Astudillo S., Mendes de Oliveira C., Olave-Rojas D. E., Lima-Dias C., Demarco R., Pallero D., Lopes A. R., Cortesi A., Telles E., Kanaan A., Ribeiro T., Schoenell W
TL;DR
The paper investigates whether star-forming compact groups (SFCGs) represent an early, pre-processing stage of compact groups by comparing their physical and morphological properties to a mass- and redshift-matched field sample. Through parametric (GALFITM) and non-parametric morphologies, plus photometric masses and UV-based SFRs, the study finds that SFCGs have elevated SFRs and sSFRs at fixed mass, while their Sérsic indices and effective radii show limited environmental differences. Approximately 16% of SFCG galaxies exhibit merger features, and these mergers display enhanced star formation, suggesting interaction-driven SF in this early CG phase. The results support a scenario where pre-processing begins with star-formation enhancement and mild morphological evolution, enabling SFCGs to serve as a valuable snapshot of CG assembly and evolution requiring follow-up spectroscopy and HI studies.
Abstract
In the context of pre-processing -- a scenario in which 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 Compact Groups (SFCGs). Our aim is to characterize the physical and morphological properties of galaxies in SFCGs, analogues of the Blue Infalling Group, and to understand how the environment influences their evolution. We use photometric techniques to derive stellar masses and star formation rates (SFRs). Morphological parameters are extracted from DECaLS images, obtaining parametric properties such as the Sérsic index ($n$) and effective radius ($R_{\mathrm{e}}$) using GALFITM, as well as non-parametric indices -- including the Gini coefficient, $M_{20}$, and asymmetry -- from the same data. These indicators allow us to classify galaxies into E/S0/Sa, Sb/Sc/Ir, and merger types. All measurements are compared to a control sample of field galaxies to assess environmental effects. We find no significant differences in $n$ and $R_{\mathrm{e}}$ between SFCG and field galaxies, in contrast to results reported for other CG samples. However, SFCG galaxies exhibit higher specific star formation rates (sSFRs) than their field counterparts. Approximately $16\%$ of SFCG galaxies show merger features and elevated asymmetry. These mergers also present enhanced SFRs compared to both other SFCG types and the field population. 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 the absence of pronounced morphological transformation. Galaxy mergers in this phase appear to enhance, rather than suppress, star formation.