Star Formation and Morphological Trends in the Antlia Cluster: Probing Environmental Influence out to 5R200

Context. Galaxy evolution in dense environments such as clusters is strongly affected by environmental processes, which can significantly alter both morphology and star formation activity. Studying galaxies over a wide range of clustercentric distances makes it possible to probe how these mechanisms operate across different environmental densities and to investigate pre-processing in the cluster infall regions. The Antlia cluster is particularly interesting due to its proximity and dynamical stage, but it still lacks investigation towards larger radii from the cluster core.
Aims. We investigate how galaxy morphology and star formation rates vary due to environmental effects, extending this analysis out to $5R_{200}$ using Southern Photometric Local Universe Survey (S-PLUS) data.
Methods. We derive star formation rates from Hα emission using the J0660-band of S-PLUS, and Sérsic index using GALFITM, for which we limit our analysis to galaxies with magnitude brighter than $m_r = 16$. Our main analysis focuses on 154 galaxies with spectroscopic redshifts consistent with the Antlia cluster. We split galaxies between early- and late-type systems (ETGs and LTGs, respectively) using a combination of colour $(u - r)$ and Sérsic index, and between quenched and star-forming (QGs and SFGs, respectively). We further explore their environmental dependence using projected phase–space diagrams, substructure, and projected local density.
Results. We find that the Antlia cluster and its infall regions are dominated by SFGs from 1 to $5R_{200}$, whereas within $1R_{200}$ it exhibits a higher fraction of QGs. ETGs and LTGs show similar radial trends to those of QGs and SFGs, respectively. However, within $1R_{200}$, Antlia exhibits approximately the same fraction of ETGs and LTGs. Regarding the local density ($\Sigma_{10}[\text{Mpc}^2]$), QGs dominate regions with $\log(\Sigma_{10}[\text{Mpc}^2]) \gtrsim 1.5$, while LTGs dominate regions with $\log(\Sigma_{10}[\text{Mpc}^2]) \lesssim 1.0$. We also identified substructures extending from the central region to the outskirts of the cluster, including substructures dominated by SFG. Nevertheless, we found that the percentage of SFG within substructures is lower than that of galaxies not associated with substructures up to $5R_{200}$ of the cluster, reinforcing the pre-processing scenario in small groups.
Conclusions. Altogether, the detected substructures indicate that the Antlia cluster is still undergoing mass assembly through group accretion, consistent with Antlia being a dynamically young system.