From blue to red spirals: Slow galaxy transformation via ram pressure stripping in TNG-50

Abstract

Late-type galaxies lose gas through ram-pressure stripping (RPS) after falling into a massive halo. Because this mechanism primarily removes the gaseous component while leaving the stellar disk largely undisturbed, it provides a pathway for quenching star formation without immediate morphological transformation. While RPS is well established in galaxy clusters, galaxy evolution in low-mass groups is often attributed to mergers, leaving open the question of whether RPS alone can drive the transition from blue, star-forming spirals to quenched systems in these environments. We use the high-resolution cosmological simulation TNG-50 to investigate the evolution of blue spiral galaxies, after their infall into group-scale halos. We excluded systems undergoing significant mergers, thus isolating the effect of RPS. We find that RPS in low-mass groups (M$_{group}<10^{14.5}$ M$_{\odot}$) can efficiently quench star formation while preserving the stellar disk structure. The transformation is gradual, with quenching timescales $\gtrsim6$ Gyr after infall, longer than the $\sim4$ Gyr typically associated with merger-driven evolution. The resulting galaxies are predominantly red, anemic spirals rather than fully transformed S0 systems, indicating that gas removal alone is insufficient to produce complete morphological transformation. Our results show that RPS in group environments can generate long-lived quenched spirals which might represent an intermediate evolutionary pathway preceding the formation of lenticular galaxies.