Spectroscopic Confirmation of a Protocluster at z = 3.37 with a High Fraction of Quiescent Galaxies
Spectroscopic Confirmation of a Protocluster at z = 3.37 with a High Fraction of Quiescent Galaxies
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DOI：
10.3847/1538-4357/ac2b9f
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发表时间：
2021-09
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通讯作者：
I. McConachie;G. Wilson;Ben Forrest;Z. C. Marsan;A. Muzzin;M. Cooper;M. Annunziatella;D. Marchesini;J. Chan;P. Gomez;Mohamed H. Abdullah;P. Saracco;J. Nantais
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作者：
I. McConachie;G. Wilson;Ben Forrest;Z. C. Marsan;A. Muzzin;M. Cooper;M. Annunziatella;D. Marchesini;J. Chan;P. Gomez;Mohamed H. Abdullah;P. Saracco;J. Nantais
我们报告在COSMOS UltraVISTA视场中发现了MAGAZ3NE J095924+022537，这是一个经过光谱确认的原星团，位于z=3.3665−0.0012+0.0009，围绕着一个经过光谱确认的uvj -静态超大质量星系（UMG; M - - - =2.34−0.34+0.23×1011M⊙）。我们提出了38个原星团成员（14个光谱和24个光度），包括UMG。值得注意的是，与之前报道的主要由恒星形成成员组成的原星团相比，我们测量到的静止星系的比例相对于同期场有所增加（73.3−16.9+26.7%，而恒星质量M -≥1011 M⊙的星系为11.6−4.9+7.1%）。这个高淬灭的部分提供了一个引人注目的重要反例，反驳了在z >2的原星团中似乎无处不在的恒星形成星系，并表明原星团在早期宇宙中以多种进化状态存在。我们讨论了我们可能观察到的“早期质量淬火”或非经典“环境淬火”的可能性。我们还发现了MAGAZ3NE J100028+023349，这是第二个光谱确认的原星团，其红移值非常相似，为z=3.3801−0.0281+0.0213。我们总共提出了20个原星团成员，其中12个是光度学的，8个是光谱学的，包括一个星暴后的UMG （M - - - =2.95−0.20+0.21×1011M⊙）。原星团MAGAZ3NE J0959和MAGAZ3NE J1000在天空中相隔18英尺（35个移动的Mpc），这与对这个时期“彗发”型星团祖先大小的模拟预测非常吻合。这两个umg极有可能是在红移较低的大质量虚拟化星团中看到的最亮星团星系的祖先。
We report the discovery of MAGAZ3NE J095924+022537, a spectroscopically confirmed protocluster at z=3.3665−0.0012+0.0009 around a spectroscopically confirmed UVJ-quiescent ultramassive galaxy (UMG; M⋆=2.34−0.34+0.23×1011M⊙ ) in the COSMOS UltraVISTA field. We present a total of 38 protocluster members (14 spectroscopic and 24 photometric), including the UMG. Notably, and in marked contrast to protoclusters previously reported at this epoch that have been found to contain predominantly star-forming members, we measure an elevated fraction of quiescent galaxies relative to the coeval field ( 73.3−16.9+26.7% versus 11.6−4.9+7.1% for galaxies with stellar mass M ⋆ ≥ 1011 M ⊙). This high quenched fraction provides a striking and important counterexample to the seeming ubiquitousness of star-forming galaxies in protoclusters at z > 2 and suggests, rather, that protoclusters exist in a diversity of evolutionary states in the early universe. We discuss the possibility that we might be observing either “early mass quenching” or nonclassical “environmental quenching.” We also present the discovery of MAGAZ3NE J100028+023349, a second spectroscopically confirmed protocluster, at a very similar redshift of z=3.3801−0.0281+0.0213 . We present a total of 20 protocluster members, 12 of which are photometric and eight spectroscopic including a poststarburst UMG ( M⋆=2.95−0.20+0.21×1011M⊙ ). Protoclusters MAGAZ3NE J0959 and MAGAZ3NE J1000 are separated by 18′ on the sky (35 comoving Mpc), in good agreement with predictions from simulations for the size of “Coma”-type cluster progenitors at this epoch. It is highly likely that the two UMGs are the progenitors of Brightest Cluster Galaxies seen in massive virialized clusters at lower redshift.