Modelling the photometric and morphological evolution of disc galaxies in the cluster environment

Compelling observational evidence indicates that the disc population in galaxy clusters has undergone rapid evolution, transitioning from a dominance of blue spirals to red lenticular galaxies (S0s) over the past ∼7 Gyr. We built a simplified cluster evolutionary model in the standard cosmological framework to constrain the characteristic timescales of this transformation. In our model, all field spirals joining the cluster at various redshifts are subject to ram-pressure stripping (RPS), which removes their gas reservoir leading to the quenching of their star formation on a timescale, t s , and to an (initially) unspecified mechanism that transforms them into S0s on a timescale, t m . We assume that t s and t m are independent and both power-law functions of the galaxy-to-cluster mass ratio, M ★ / M cl . We constrained our model using the observed distribution of spirals and S0s in a colour-mass plane from the OmegaWINGS and EDisCS cluster surveys at z ≃ 0.055 and z ≃ 0.7, respectively. Our best-fit model reproduces the data remarkably well, especially at low redshift, and predicts evolutionary trends for the main morphological fractions in agreement with previous studies. We find typical t s values between 0.1 and 1 Gyr, compatible with previous estimates, supporting RPS as the most efficient quenching mechanisms in clusters. A surprisingly strong anti-correlation between t s and M ★ / M cl is required in order to suppress the formation of red, low-mass spirals at low redshift, which we interpret as being driven by orbit anisotropy. Conversely, t m depends very weakly on M ★ / M cl and has typical values of a few Gyr. The inferred morphological evolution is compatible with that resulting from the ageing of the stellar populations in galaxies that have been abruptly quenched by ram pressure stripping: we confirm spectrophotometric ageing as a key channel for the spiral-to-S0 transition in galaxy clusters, with secular evolution playing a secondary role.