The ionizing properties of two bright Ly a emitters in the Bremer Deep Field reionized bubble at z = 7
The ionizing properties of two bright Ly a emitters in the Bremer Deep Field reionized bubble at z = 7
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布雷默深场再电离气泡中 z = 7 处两个明亮 Ly a 发射体的电离特性
DOI：
10.1051/0004-6361/202243348
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发表时间：
2022
影响因子：
6.5
通讯作者：
Castellano M
中科院分区：
文献类型：
--
作者：
Castellano M
目的研究明亮的Lyα发射星系BDF521和BDF2195 atz= 7.012的电离性质，以限制它们对布雷默深场“电离泡”的形成的贡献。方法我们从深部λX-Shooter观测中获得了4条UV发射线的约束条件(CIVλ1548双线、HeIIλ1640、OIII]λ1660双线和CIII]AGN 1909双线，并将它们与其他高红移天体以及恒星和活动星系核混合发射的模型进行了比较。我们使用这些光谱信息，以及现场可用的光度学，使用光谱光度拟合程序BEAGLE.来约束这两个对象的物理性质。结果我们没有在UV线的预期位置检测到任何显著的发射，具有3σ上限的等效宽度(EW)≲2-7？REST-Frame。根据Lyα和CIII]EWS之间的关联，我们发现这两个天体的CIII]排放比预期的要低。CIV和HeII发射的EW限制排除了∼2 − 3σ意义上的纯活动星系核模板，只有≲贡献40%活动星系核的模型才与观测结果兼容。这两个天体被发现相对年轻(∼20-30Myr)和贫金属(≲0.3Z⊙)，恒星质量只有109m⊙。它们每本征紫外光度的氢电离光子产生率为Log(/Hzerg−1)=2 5.0 2-2 5.2 6，与高红移星系中的典型数值一致，但比强CIII和/或光谱线发射(BDF2 5.6-2 5.7)的Z>； 7星系的测量值低两倍以上。结论这两个≃发射体没有证据表明它们的电离能力高于平均水平，而且在电离光子逃逸比例的现实假设下，它们不能用自己的方法电离周围环境。因此，对电离气泡形成的主要贡献一定是由较暗的伴星系提供的。这些天体的光谱确认将需要詹姆斯·韦伯太空望远镜的能力。
AimsWe investigate the ionizing properties of the pair of bright Lyαemitting galaxies BDF521 and BDF2195 atz= 7.012 in order to constrain their contribution to the formation of the Bremer Deep Field (BDF) ‘reionized bubble’ in which they have been shown to reside.MethodsWe obtain constraints on four UV emission lines (the CIVλ1548 doublet, HeIIλ1640, the OIII]λ1660 doublet, and the CIII]λ1909 doublet) from deep VLT X-shooter observations and compare them to those available for other high-redshift objects, and to models with mixed stellar and active galactic nucleus (AGN) emission. We use this spectroscopic information, together with the photometry available in the field, to constrain the physical properties of the two objects using the spectro-photometric fitting code BEAGLE.ResultsWe do not detect any significant emission at the expected position of the UV lines, with 3σupper limits of equivalent width (EW) ≲2–7 Å rest-frame. We find that the two objects have a lower CIII] emission than expected on the basis of the correlation between the Lyαand CIII] EWs. The EW limits on CIV and HeII emission exclude pure AGN templates at ∼2 − 3σsignificance, and only models with a ≲40% AGN contribution are compatible with the observations. The two objects are found to be relatively young (∼20–30 Myrs) and metal-poor (≲0.3Z⊙), with stellar masses of a few 109M⊙. Their production rate of hydrogen ionizing photons per intrinsic UV luminosity is log( /Hz erg−1) = 25.02–25.26, consistent with values typically found in high-redshift galaxies, but more than twice lower than values measured inz> 7 galaxies with strong CIII] and/or optical line emission (≃25.6–25.7).ConclusionsThe two BDF emitters show no evidence of higher-than-average ionizing capabilities and are not capable of reionizing their surroundings by their own means, under realistic assumptions of the escape fraction of ionizing photons. Therefore, a dominant contribution to the formation of the reionized bubble must have been provided by fainter companion galaxies. The capabilities of theJames WebbSpace Telescope will be needed for spectroscopic confirmation of these objects.