2024MNRAS.530.3310O

We illuminate the altered evolution of galaxies in clusters compared to central galaxies by tracking galaxies in the IllustrisTNG300 simulation as they enter isolated clusters of mass 10¹³ < M_200,mean/M_⊙ < 10¹⁵ (at z = 0). We demonstrate significant trends in galaxy properties with residence time (time since first infall) and that there is a population of galaxies that remain star forming even many Gyr after their infall. By comparing the properties of galaxies at their infall time to their properties at z = 0, we show how scaling relations, like the stellar-to-halo mass ratio, shift as galaxies live in the cluster environment. Galaxies with a residence time of 10 Gyr increase their stellar-to-halo mass ratio, by around 1 dex. As measurements of the steepest slope of the galaxy cluster number density profile (R_st), frequently used as a proxy for the splashback radius, have been shown to depend strongly on galaxy selection, we show how R_st depends on galaxy residence time. Using galaxies with residence times less than one cluster crossing time (≈5 Gyr) to measure R_st leads to significant offsets relative to using the entire galaxy population. Galaxies must have had the opportunity to 'splash back' to the first caustic to trace out a representative value of R_st, potentially leading to issues for galaxy surveys using ultraviolet-selected galaxies. Our work demonstrates that the evolution of cluster galaxies continues well into their lifetime in the cluster and departs from a typical central galaxy evolutionary path.