摘要
Recent JWST observations have revealed an overabundance of quiescent galaxies at high redshift. Photometric methods, such as photometry-derived sSFRs,UVJcolors, and syntheticugi_(s)colors, are commonly used to identify quiescent galaxies, but their completeness and purity remain poorly constrained. Here we present a spectroscopically selected sample of 19 quiescent galaxies at2 ≤ z ≤ 4from the CANDELS-Area Prism Epoch of Reionization Survey (CAPERS). They are selected withM_(∗) > 10^(9.5) M_(⊙)and a specific star formation rate below 20% of the inverse cosmic age. These galaxies formed 50% of their stellar mass atz ∼ 3.0 –4.6 and quenched rapidly on timescales of∼0.1 –0.2 Gyr. These quenching timescales are comparable to those of other high-redshift QGs but shorter than those at lower redshift. Using the spectroscopic sample as a benchmark, we assess commonly adopted photometric QG selection methods. We find completeness of 63–89% and purities of only 40–63%, with strong emission-line galaxies constituting the dominant source of contamination. Applying completeness and purity corrections calibrated from the spectroscopic sample, we measure the number density of quiescent galaxies at2 ≤ z ≤ 5 . The resulting number densities exceed the predictions of most current galaxy-formation simulations at2<z<4 , with the largest discrepancy atM_(∗) ≥ 10^(10.5) M_(⊙) . This discrepancy suggests that current cosmological models may not assemble and quench massive galaxies sufficiently early or efficiently.