Too dense to go through: the role of low-mass clusters in the pre-processing of satellite galaxies.

We study the evolution of satellite galaxies in clusters of the c-eagle simulations, a suite of 30 high-resolution cosmological hydrodynamical zoom-in simulations based on the eagle code. We find that the majority of galaxies that are quenched at z  = 0 (≳80 |${{\ \rm per\ cent}}$|⁠) reached this state in a dense environment (log₁₀M₂₀₀[M_⊙] ≥13.5). At low redshift, regardless of the final cluster mass, galaxies appear to reach their quenching state in low-mass clusters. Moreover, galaxies quenched inside the cluster that they reside in at z  = 0 are the dominant population in low-mass clusters, while galaxies quenched in a different halo dominate in the most massive clusters. When looking at clusters at z > 0.5, their in situ quenched population dominates at all cluster masses. This suggests that galaxies are quenched inside the first cluster they fall into. After galaxies cross the cluster's r ₂₀₀ they rapidly become quenched (≲1 Gyr). Just a small fraction of galaxies (⁠|$\lesssim 15{{\ \rm per\ cent}}$|⁠) is capable of retaining their gas for a longer period of time, but after 4 Gyr, almost all galaxies are quenched. This phenomenon is related to ram pressure stripping and is produced when the density of the intracluster medium reaches a threshold of |$\rho _{\rm ICM}\, \sim 3 \times 10 ^{-5}$| n_H (cm⁻³). These results suggest that galaxies start a rapid-quenching phase shortly after their first infall inside r ₂₀₀ and that, by the time they reach r ₅₀₀, most of them are already quenched. [ABSTRACT FROM AUTHOR]