Investigating the growing population of massive quiescent galaxies at cosmic noon

Abstract

We explore the buildup of quiescent galaxies using a sample of 28,469 massive (𝑀★ ≥ 1011M ) galaxies at redshifts 1.5 < 𝑧 < 3.0, drawn from a 17.5 deg2 area (0.33 Gpc3 comoving volume at these redshifts). This allows for a robust study of the quiescent fraction as a function of mass at 1.5 < 𝑧 < 3.0 with a sample ∼40 times larger at log(𝑀★/M )≥ 11.5 than previous studies. We derive the quiescent fraction using three methods: specific star-formation rate, distance from the main sequence, and UVJ color-color selection. All three methods give similar values at 1.5 < 𝑧 < 2.0, however the results differ by up to a factor of two at 2.0 < 𝑧 < 3.0. At redshifts 1.5 < 𝑧 < 3.0 the quiescent fraction increases as a function of stellar mass. By 𝑧 = 2, only 3.3 Gyr after the Big Bang, the universe has quenched ∼25% of 𝑀★ = 1011M galaxies and ∼45% of 𝑀★ = 1012M galaxies. We discuss physical mechanisms across a range of epochs and environments that could explain our results. We compare our results with predictions from hydrodynamical simulations SIMBA and IllustrisTNG and semi-analytic models (SAMs) SAG, SAGE, and Galacticus. The quiescent fraction from IllustrisTNG is higher than our empirical result by a factor of 2 − 5, while those from SIMBA and the three SAMs are lower by a factor of 1.5 − 10 at 1.5 < 𝑧 < 3.0.