Quenched fractions in the IllustrisTNG simulations: comparison with observations and other theoretical models

We make an in-depth comparison of the IllustrisTNG cosmological simulations with observed quenched fractions of central and satellite galaxies, for M-stars = 10(9-12) M-circle dot at 0 <= z <= 3. We show how measurement choices [aperture, quenched definition, and star formation rate (SFR) indicator time-scale], as well as sample selection issues (projection effects, satellite/central misclassification, and host mass distribution sampling), impact this comparison. The quenched definition produces differences of up to 70 (30) percentage points for centrals (satellites) above similar to 10(10.5) M-circle dot. At z greater than or similar to 2, a larger aperture within which SFR is measured suppresses the quenched fractions by up to similar to 50 percentage points. Proper consideration of the stellar and host mass distributions is crucial: Naive comparisons to volume-limited samples from simulations lead to misinterpretation of the quenched fractions as a function of redshift by up to 20 percentage points. Including observational uncertainties to theoretical values of M-stars and SFR changes the quenched fraction values and their trend and/or slope with mass. Taking projected rather than three-dimensional distances for satellites decreases the quenched fractions by up to 10 percent. TNG produces quenched fractions for both centrals and satellites broadly consistent with observations and predicts up to similar to 80 (90) percent of quenched centrals at z = 0 (z = 2), in line with recent observations, and higher than other theoretical models. The quantitative agreement of TNG and Sloan Digital Sky Survey for satellite quenched fractions in groups and clusters depends strongly on the galaxy and host mass range. Our mock comparison highlights the importance of properly accounting for observational effects and biases.

Automated summary

Comparing IllustrisTNG cosmological simulations with observed quenched fractions of galaxies reveals significant impact from measurement choices and sample selection. Proper consideration of stellar and host mass distributions is crucial, and incorporating observational uncertainties changes quenched fraction values and trends.