[论文解读] The FENIKS Survey: Spectroscopic Confirmation of Massive Quiescent Galaxies at z ~ 3-5

Jacqueline Antwi-Danso, Casey Papovich+14 more|arXiv (Cornell University)|Jul 18, 2023

Astronomy and Astrophysical Research被引用 8

一句话总结

作者基于 Keck/MOSFIRE 光谱确认来自 FENIKS 调查的三个人们质稳态星系（其中一个在 z=3.757 为确定，另外两个在 z=3.336 和 z=4.673 呈不确定）以及一个 AGN 在 z=3.594，结果对早期大质量星系的年龄与祖先有意义。

ABSTRACT

The measured ages of massive, quiescent galaxies at $z\sim 3-4$ imply that massive galaxies quench as early as $z\sim 6$. While the number of spectroscopic confirmations of quiescent galaxies at $z < 3$ has increased over the years, there are only a handful at $z > 3.5$. We report spectroscopic redshifts of one secure ($z=3.757$) and two tentative ($z = 3.336$, $z=4.673$) massive ($\log(M_\ast/M_\odot) > 10.3$) quiescent galaxies with 11 hours of Keck/MOSFIRE $K$-band observations. Our candidates were selected from the FENIKS survey, which uses deep Gemini/Flamingos-2 $K_b$ $K_r$ imaging optimized for increased sensitivity to the characteristic red colors of galaxies at $z > 3$ with strong Balmer/4000 Å breaks. The rest-frame $UVJ$ and $(ugi)_s$ colors of 3/4 quiescent candidates are consistent with $1-2$ Gyr old stellar populations. This places these galaxies as the oldest objects at these redshifts, and challenges the notion that quiescent galaxies at $z > 3$ are all recently-quenched, "post-starburst" galaxies. Our spectroscopy shows that the other quiescent-galaxy candidate is a broad-line AGN ($z = 3.594$) with strong, redshifted $Hβ$+[O III] emission with a velocity offset $>1000$ km/s, indicative of a powerful outflow. The star-formation history of our highest redshift candidate suggests that its progenitor was already in place by $z \sim 7-11$, reaching $\sim$ 10$^{11} M_{\odot}$ by $z \simeq 8$. These observations reveal the limit of what is possible with deep near-infrared photometry and targeted spectroscopy from the ground and demonstrate that secure spectroscopic confirmation of quiescent galaxies at $z > 4$ is only feasible with JWST.

研究动机与目标

• 以稳健方式约束早期宇宙中最巨大的星系的形成与抑制的研究动机。
• 获取来自 FENIKS 选择的 z>3 大质量稳态星系候选对象的光谱红移。
• 表征恒星族群、静止系颜色和恒星形成历史，以评估年龄与祖先。

提出的方法

• 使用深层 Gemini/Flamingos-2 K 波段分割成像（Kb 与 Kr）来选择具有强 Balmer/4000 Å 转折的高-z 稳态候选对象。
• 获取 11 小时 Keck/MOSFIRE K 波段光谱，检测来自 z>3.3 的连续谱与吸收线（以及 AGN 的发射线）。
• 使用 slit stars 做大气校正，进行最佳加权的一维光谱提取与通量校准。
• 用 eazy-py 与 Bagpipes 拟合光度测量，推导光度学红移、光度学红移和恒星群参数。
• 联合拟合光度测量和光谱，使用 Bagpipes，采用九参数模型，包括双幂律型星形成历史、金属丰度、尘埃及发射线。
• 使用 slinefit 独立地通过吸收特征与线比估计光谱中的红移。

Figure 1: 11 ′′ $\times$ 11 ′′ image stamps and photometric redshift solutions for our four $\log(M_{\ast}/M_{\odot})>10$ quiescent candidates and broad-line AGN. The $K$ -band images are convolved to match a PSF with FWHM=1.05 ′′ . The faintest candidates have markers next to them to distinguish th

实验结果

研究问题

• RQ1 在当前地基近红外设施下，是否能够通过光谱确认 z>3 的大质量稳态星系？
• RQ2 这些高-z 稳态系统的年龄、恒星质量、星形成历史与静止系颜色是什么？
• RQ3 有多少候选对象实际是稳态星系、而不是 AGN 或星形成星系，且在 z>4 时地基探测存在哪些偏差？
• RQ4 这些系统对其祖先与形成时段（如 z~7-11）的含义是什么？

主要发现

• 三个稳态星系候选对象的光谱红移得到确认：其中一个在 z=3.757，另外两个在 z=3.336 和 z=4.673 为不确定。
• 其中一个候选对象是 z=3.594 的宽线型 AGN，具强烈的红移 Hβ + [O III] 发射，指示强烈的流出。
• 3/4 的稳态候选对象的原始帧 UVJ 及 (ugi)s 颜色与 1–2 Gyr 的恒星族群相一致。
• 最高红移候选对象的星形成史表明其祖先在 z~7–11 时已建立，至 z~10 达到约 10^11 M⊙。
• 这些结果突显了地基近红外深度光度与光谱确认 z>4 的极限，强调 JWST 对于 z>4 光谱的必要性。
• 研究强调并非所有 z>3 的稳态星系都是最近熄灭的后爆发星，而是在这一纪元内可能是较早的族群。

Figure 2: From left to right: 11-hour MOSFIRE spectra, redshift probability distribution, and false-color images of our candidates. The spectra are arranged in order of increasing redshift. For display purposes, we smoothed the 2D spectra with a 0.7 ′′ FWHM Gaussian in the spatial direction . Note t