A study on the multicolour evolution of Red Sequence galaxy populations: insights from hydrodynamical simulations and semi-analytical models

Abstract: By means of our own cosmological-hydrodynamical simulation and semi-analytical model we studied galaxy population properties in clusters and groups, spanning over 10 different bands from UV to NIR, and their evolution since redshift z=2. We compare our results in terms of galaxy red/blue fractions and luminous-to-faint ratio (LFR) on the Red Sequence (RS) with recent observational data reaching beyond z=1.5. Different selection criteria were tested in order to retrieve galaxies belonging to the RS: either by their quiescence degree measured from their specific SFR ("Dead Sequence"), or by their position in a colour-colour plane which is also a function of sSFR. In both cases, the colour cut and the limiting magnitude threshold were let evolving with redshift, in order to follow the natural shift of the characteristic luminosity in the LF. We find that the Butcher-Oemler effect is wavelength-dependent, with the fraction of blue galaxies increasing steeper in optical colours than in NIR. Besides, only when applying a lower limit in terms of fixed absolute magnitude, a steep BO effect can be reproduced, while the blue fraction results less evolving when selecting samples by stellar mass or an evolving magnitude limit. We then find that also the RS-LFR behaviour, highly debated in the literature, is strongly dependent on the galaxy selection function: in particular its very mild evolution recovered when measured in terms of stellar mass, is in agreement with values reported for some of the highest redshift confirmed (proto)clusters. As to differences through environments, we find that normal groups and (to a lesser extent) cluster outskirts present the highest values of both star forming fraction and LFR at low z, while fossil groups and cluster cores the lowest: this separation among groups begins after z~0.5, while earlier all group star forming properties are undistinguishable.