Some of the leading simulations of the star formation process in galaxies don't reflect the mix of star forming galaxies and galaxies that are passive and not forming many new stars that is observed, while some of the less popular simulations do. This suggests that the errant simulations are missing some important principle.
The specific star formation rate function at different mass scales and quenching: A comparison between cosmological models and SDSS
We present the eddington bias corrected Specific Star Formation Rate Function (sSFRF) at different stellar mass scales from a sub-sample of the Sloan Digital Sky Survey Data Release DR7 (SDSS), which is considered complete both in terms of stellar mass () and star formation rate (SFR). The above enable us to study qualitatively and quantitatively quenching, the distribution of passive/star-forming galaxies and perform comparisons with the predictions from state-of-the-art cosmological models, within the same and SFR limits. We find that at the low mass end ( ) the sSFRF is mostly dominated by star-forming objects. However, moving to the two more massive bins ( and ) a bi-modality with two peaks emerges. One peak represents the star-forming population, while the other describes a rising passive population. The bi-modal form of the sSFRFs is not reproduced by a range of cosmological simulations (e.g. Illustris, EAGLE, Mufasa, IllustrisTNG) which instead generate mostly the star-forming population, while a bi-modality emerges in others (e.g. L-Galaxies, Shark, Simba). Our findings reflect the need for the employed quenching schemes in state-of-the-art models to be reconsidered, involving prescriptions that allow "quenched galaxies" to retain a small level of SF activity (sSFR - ) and generate an adequate passive population/bi-modality even at intermediate masses ( ).