Demography and morphological evolution of red spirals and S0s in groups and clusters

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In this study, we analyse a sample of 4228 galaxies in groups and clusters to understand the morphological changes during their infall into these systems. We introduce a new classification method that combines the second gradient moment (G₂) and Shannon entropy (H) with the T-Type parameter, identifying early, late, and transitional types. Our findings reveal that transitional galaxies, comprising 24 per cent of the sample, predominantly occupy intermediate regions in the projected phase space, suggesting times since infall between 3.6 and 6.5 Gyr. These galaxies, mainly red spirals with enlarged bulges and high metallicities, are prevalent in groups, indicating significant evolutionary activity in systems with M₂₀₀ ≤ 10¹⁴ M_, where 63 per cent of transitional galaxies are located. Our results suggest a two-step evolutionary pathway: disc galaxies develop enhanced bulges and suppressed star formation, evolving into red spirals and subsequently into lenticulars, with metallicity enrichment and structural reconfiguration accompanying this process. These findings provide new insights into how environmental mechanisms drive galaxy evolution.