Star-forming and quiescent galaxies in synthetic spectroscopic surveys from cosmological simulations

The populations of star-forming, green valley, and quiescent galaxies, whether predicted from simulations or observed, vary depending on how these are defined and on the tracers used to measure star formation rates. We explore star formation and quiescence of galaxies in 6 largescale cosmological simulations and compare apples-to-apples to observational data. We carefully build synthetic galaxy spectra for all (~3e5) simulated galaxies and (re)measure star formation and quenching indicators. Using this wealth of spectral data, we describe the populations of star-forming and quiescent galaxies in simulations, in synthetic observations, and in observational data, and carefully compare. This allows us to connect the different quenching mechanisms in the simulations to trends in the (mock) observational indicators. Additionally, we combine our observational and theoretical knowledge to provide comparisons and conversions for a number of observational quenching and quiescence indicators.