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arXiv 1504.07686astro-ph.GA
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再电离时期CIII ]发射的初步观测:前沿场星系团Abell 2744中的引力透镜z $\sim7-8$星系团

A Pilot Survey for CIII] Emission in the Reionization Era: Gravitationally-Lensed z$\sim7-8$ Galaxies in the Frontier Fields Cluster Abell 2744

Adi Zitrin, Richard S. Ellis, Sirio Belli, Dan P. Stark

摘要:

我们报告了用凯克的MOSFIRE摄谱仪在哈勃前沿场星团Abell 2744透镜下的7个$z_{phot}\sim7-8$候选者($H\sim27$)样本中搜索CIII] $λλ$ 1907,1909的结果。早期的工作表明,如果$Lyα$($λ$ 1216)可能被中性星系际介质衰减,那么在再电离时代使用CIII]双重态来确认星系的红移是有希望的。这种方法的主要挑战是在没有光谱红移的先进知识的情况下定位CIII]发射的可行性。在H波段的积分时间为5小时,我们达到了$5σ$的中位通量极限(在天际线之间)为$1.5\times10^{-18}$尔格cm $^{-2}$ sec $^{-1}$,但没有发现令人信服的CIII]发射。我们还结合了另外两个CLASH/HFF星系团的初步测量,同样,没有检测到谱线,但这些观测到的深度较小。使用已知的OH发射分布和每个透镜候选者的光度红移似然分布,我们提出了我们的$z\simeq7-8$样本的平均总CIII]静止帧等效宽度的统计上限。对于信噪比为5的情况,我们估计典型的CIII]双峰静止帧等效宽度为$<26\pm5$ π,置信度为95%。虽然与$z\simeq6-7$早期探测到的较亮天体的强度一致,但我们的研究说明了在詹姆斯韦伯太空望远镜发射之前研究更明亮或强透镜的例子的必要性。

英文摘要:

We report results of a search for CIII] $λλ$1907,1909 Å emission using Keck's MOSFIRE spectrograph in a sample of 7 $z_{phot}\sim7-8$ candidates ($H\sim27$) lensed by the Hubble Frontier Field cluster Abell 2744. Earlier work has suggested the promise of using the CIII] doublet for redshift confirmation of galaxies in the reionization era given $Lyα$ ($λ$1216 Å) is likely attenuated by the neutral intergalactic medium. The primary challenge of this approach is the feasibility of locating CIII] emission without advanced knowledge of the spectroscopic redshift. With an integration time of 5 hours in the H-band, we reach a $5σ$ median flux limit (in between the skylines) of $1.5\times10^{-18}$ ergs cm$^{-2}$ sec$^{-1}$ but no convincing CIII] emission was found. We also incorporate preliminary measurements from two other CLASH/HFF clusters in which, similarly, no line was detected, but these were observed to lesser depth. Using the known distribution of OH emission and the photometric redshift likelihood distribution of each lensed candidate, we present statistical upper limits on the mean total CIII] rest-frame equivalent width for our $z\simeq7-8$ sample. For a signal/noise ratio of 5, we estimate the typical CIII] doublet rest-frame equivalent width is, with 95\% confidence, $<26\pm5$ Å. Although consistent with the strength of earlier detections in brighter objects at $z\simeq6-7$, our study illustrates the necessity of studying more luminous or strongly-lensed examples prior to the launch of the James Webb Space Telescope.

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