来自CAPERS光谱的$z > 2$静止星系及其数密度
Quiescent Galaxies at $z > 2$ from CAPERS spectroscopy and their Number densities
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中文总结 AI 辅助
基于CAPERS光谱选出19个z=2-4静止星系，评估光度选择法完备度63-89%、纯净度40-63%，修正后数密度高于模拟预测，暗示模型对高红移大质量星系形成与熄灭不足。
中文摘要 AI 辅助
最近的JWST观测揭示了高红移处静止星系的数量过剩。光度方法，如基于测光得出的恒星形成率比（sSFR）、$UVJ$颜色和合成$ugi_s$颜色，常用于识别静止星系，但其完备性和纯净度仍缺乏严格约束。在此，我们展示了来自CANDELS区域棱镜再电离纪元巡天（CAPERS）的光谱选出的19个静止星系样本，红移范围为$2 \leq z \leq 4$。这些星系的选择条件为恒星质量$M_\ast > 10^{9.5} M_\odot$且恒星形成率比低于宇宙年龄倒数的20%。这些星系在$z \sim 3.0$--4.6时形成了其恒星质量的50%，并在约0.1--0.2 Gyr的时间尺度上迅速熄灭。这些熄灭时间尺度与其他高红移静止星系相当，但短于较低红移的静止星系。以该光谱样本为基准，我们评估了常用的光度静止星系选择方法。我们发现完备度为63--89%，纯净度仅为40--63%，其中强发射线星系是主要的污染源。应用基于光谱样本校准的完备度和纯净度修正，我们测量了$2 \leq z \leq 5$范围内静止星系的数密度。得到的数密度在$2<z<4$时超过了大多数当前星系形成模拟的预测，在$M_\ast \geq 10^{10.5} M_\odot$处差异最大。这一差异表明，当前的宇宙学模型可能未能足够早或足够有效地组装和熄灭大质量星系。
英文摘要
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 $2 \leq z \leq 4$ from the CANDELS-Area Prism Epoch of Reionization Survey (CAPERS). They are selected with $M_\ast > 10^{9.5} M_\odot$ and a specific star formation rate below 20% of the inverse cosmic age. These galaxies formed 50% of their stellar mass at $z \sim 3.0$--4.6 and quenched rapidly on timescales of $\sim0.1$--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 $2 \leq z \leq 5$. The resulting number densities exceed the predictions of most current galaxy-formation simulations at $2<z<4$, with the largest discrepancy at $M_\ast \geq 10^{10.5} M_\odot$. This discrepancy suggests that current cosmological models may not assemble and quench massive galaxies sufficiently early or efficiently.
发表机构
- Texas A&M University（德克萨斯农工大学）
- George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University（乔治·P和辛西娅·伍兹基础物理与天文学研究所，德克萨斯农工大学）
- NSF NOIRLab（美国国家科学基金会NOIR天文台）
- Center for Space Sciences and Technology, UMBC（UMBC空间科学与技术中心）
- Astrophysics Science Division, NASA Goddard Space Flight Center（NASA戈达德太空飞行中心天体物理学科学部）
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