Quiescent Galaxies at z > 2 from CAPERS spectroscopy and their Number densities
Abstract
Recent JWST observations have revealed an overabundance of quiescent galaxies at high redshift. Photometric methods, such as photometry-derived sSFRs, UVJ colors, and synthetic ugis 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 at 2 ≤ z ≤ 4 from the CANDELS-Area Prism Epoch of Reionization Survey (CAPERS). They are selected with M∗ > 109.5 M⊙ and a specific star formation rate below 20% of the inverse cosmic age. These galaxies formed 50% of their stellar mass at z ∼ 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 at 2 ≤ z ≤ 5. The resulting number densities exceed the predictions of most current galaxy-formation simulations at 2<z<4, with the largest discrepancy at M∗ ≥ 1010.5 M⊙. This discrepancy suggests that current cosmological models may not assemble and quench massive galaxies sufficiently early or efficiently.
Related
- PANORAMIC: The Dawn of Massive Quiescent Galaxies. I. Number Density and Cosmic Variance from 1000 arcmin ² NIRCam Imaging
- Caught Napping by JWST UNCOVER+MegaScience: Constraining bursty star formation histories and number densities of mini-quenched galaxies at redshifts 4-7
- Evolution of the morphology-density and morphology-mass relations of quiescent galaxies at 0.5 {2}lt;z<$ 2.5 in the COSMOS-Web survey
- The Role of Environment in Shaping the Assembly Timelines of Massive Quiescent Galaxies at Cosmic Noon
- The Stellar Populations of Two Quiescent Low Surface Brightness Dwarf Galaxies in Low Density Environments
BibTeX
@misc{shen2026quiescent,
title = {{Quiescent Galaxies at $z > 2$ from CAPERS spectroscopy and their Number densities}},
author = {Lu Shen and Weida Hu and Casey Papovich and Justin Cole and Mark Dickinson and Pablo Arrabal Haro and Anthony J. Taylor and Adam C. Carnall and Ángel Chandro-Gómez and Yingjie Cheng and Nikko J. Cleri and James S. Dunlop and Carter Flayhart and Steven L. Finkelstein and Mauro Giavalisco and Michaela Hirschmann and Eric F. Jiménez-Andrade and Jeyhan S. Kartaltepe and Claudia D. P. Lagos and Ho-Hin Leung and Arianna S. Long and Ray A. Lucas and Eric J. Murphy and Lorenzo Napolitano and Pablo G. Pérez-González and Raymond C. Simons and Struan D Stevenson and Elizabeth Taylor and Xin Wang and L. Y. Aaron Yung and Jorge A. Zavala},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.20931},
eprint = {2609.20931},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.20931},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Quiescent Galaxies at z > 2 from CAPERS spectroscopy and their Number densities
AU - Lu Shen
AU - Weida Hu
AU - Casey Papovich
AU - Justin Cole
AU - Mark Dickinson
AU - Pablo Arrabal Haro
AU - Anthony J. Taylor
AU - Adam C. Carnall
AU - Ángel Chandro-Gómez
AU - Yingjie Cheng
AU - Nikko J. Cleri
AU - James S. Dunlop
AU - Carter Flayhart
AU - Steven L. Finkelstein
AU - Mauro Giavalisco
AU - Michaela Hirschmann
AU - Eric F. Jiménez-Andrade
AU - Jeyhan S. Kartaltepe
AU - Claudia D. P. Lagos
AU - Ho-Hin Leung
AU - Arianna S. Long
AU - Ray A. Lucas
AU - Eric J. Murphy
AU - Lorenzo Napolitano
AU - Pablo G. Pérez-González
AU - Raymond C. Simons
AU - Struan D Stevenson
AU - Elizabeth Taylor
AU - Xin Wang
AU - L. Y. Aaron Yung
AU - Jorge A. Zavala
PY - 2026
DA - 2026/09/17
PB - arXiv
DO - 10.48550/arxiv.2609.20931
UR - https://arxiv.org/abs/2609.20931
AB - Recent JWST observations have revealed an overabundance of quiescent galaxies at high redshift. Photometric methods, such as photometry-derived sSFRs, UVJ colors, and synthetic ugi_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 at 2 ≤ z ≤ 4 from the CANDELS-Area Prism Epoch of Reionization Survey (CAPERS). They are selected with M_∗ > 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 at z ∼ 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 at 2 ≤ z ≤ 5. The resulting number densities exceed the predictions of most current galaxy-formation simulations at 2<z<4, with the largest discrepancy at M_∗ ≥ 10^10.5 M_⊙. This discrepancy suggests that current cosmological models may not assemble and quench massive galaxies sufficiently early or efficiently.
ER -