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arXiv 1507.02679astro-ph.GAastro-ph.CO
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一个z=8.68的明亮星系的莱曼α辐射:星系核作为宇宙再电离示踪物的意义

Lyman-alpha Emission from a Luminous z=8.68 Galaxy: Implications for Galaxies as Tracers of Cosmic Reionization

Adi Zitrin, Ivo Labbe, Sirio Belli, Rychard Bouwens, Richard S. Ellis, Guido Roberts-Borsani, Daniel P. Stark, Pascal A. Oesch, Renske Smit

摘要:

我们报告了在凯克天文台使用MOSFIRE摄谱仪在明亮的星系EGSY-2008532660(以下简称EGSY 8 p7)中发现的莱曼α发射(Ly $α$)。首先由Roberts-Borsani等人(2015)报道,它被选择用于光谱观测,因为它的光度红移($z_{phot}=8.57^{+0.22}_{-0.43}$),表观亮度(H $_{160}=25.26\pm0.09$)和红色斯皮策/IRAC [3.6]-[4.5]颜色指示[4.5]带中的强氧发射污染。总积分的$\sim$ 4.3小时,我们的数据揭示了在$\simeq$ 11776的发射线,我们认为这可能是在红移$z_{spec}=8.683^{+0.001}_{-0.004}$的Ly $α$,在良好的协议与测光估计。在两个晚上使用不同的狭缝取向独立地检测到该线,其检测意义为$\sim7.5σ$。一个重叠的天际线有助于显着的不确定性的总线通量,虽然检测到的线的意义是强大的各种天际线掩蔽程序。通过直接相加和高斯拟合,我们估计95%置信范围为1.0--2.5 $\times10^{-17}$ erg s $^{-1}$ cm $^{-2}$,对应于17--42 mm的静息帧等效宽度。EGSY 8 p7是迄今为止通过光谱确认的最遥远的星系,也是EGS领域中第三个发光源,超过了$z_{phot}\gtrsim7.5$,在星系际介质被认为是相当中性的时候,可以检测到Ly $α$发射。虽然再电离过程可能是不完整的,我们讨论是否发光的光源与突出的IRAC颜色过剩可能窝藏更难的电离光谱比占主导地位的微弱人口,从而创造早期的电离气泡。对这些明亮光源的进一步光谱跟踪有望对星系的早期形成有重要的了解。

英文摘要:

We report the discovery of Lyman-alpha emission (Ly$α$) in the bright galaxy EGSY-2008532660 (hereafter EGSY8p7) using the MOSFIRE spectrograph at the Keck Observatory. First reported by Roberts-Borsani et al. (2015), it was selected for spectroscopic observations because of its photometric redshift ($z_{phot}=8.57^{+0.22}_{-0.43}$), apparent brightness (H$_{160}=25.26\pm0.09$) and red Spitzer/IRAC [3.6]-[4.5] color indicative of contamination by strong oxygen emission in the [4.5] band. With a total integration of $\sim$4.3 hours, our data reveal an emission line at $\simeq$11776 Å which we argue is likely Ly$α$ at a redshift $z_{spec}=8.683^{+0.001}_{-0.004}$, in good agreement with the photometric estimate. The line was detected independently on two nights using different slit orientations and its detection significance is $\sim7.5σ$. An overlapping skyline contributes significantly to the uncertainty on the total line flux although the significance of the detected line is robust to a variety of skyline-masking procedures. By direct addition and a Gaussian fit, we estimate a 95\% confidence range of 1.0--2.5$\times10^{-17}$ erg s$^{-1}$ cm$^{-2}$, corresponding to a rest-frame equivalent width of 17--42 Å. EGSY8p7 is the most distant galaxy confirmed spectroscopically to date, and the third luminous source in the EGS field beyond $z_{phot}\gtrsim7.5$ with detectable Ly$α$ emission viewed at a time when the intergalactic medium is believed to be fairly neutral. Although the reionization process was probably patchy, we discuss whether luminous sources with prominent IRAC color excesses may harbor harder ionizing spectra than the dominant fainter population thereby creating earlier ionized bubbles. Further spectroscopic follow-up of such bright sources promises important insight into the early formation of galaxies.

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