New constraints on the average escape fraction of Lyman continuum radiation in z~4 galaxies from the VIMOS Ultra Deep Survey (VUDS)
New constraints on the average escape fraction of Lyman continuum radiation in z~4 galaxies from the VIMOS Ultra Deep Survey (VUDS)
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VIMOS 超深巡天 (VUDS) 对 z~4 星系中莱曼连续谱辐射平均逃逸分数的新约束
DOI：
10.1051/0004-6361/201630054
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发表时间：
2016
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影响因子：
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通讯作者：
E. Zucca
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作者：
F. Marchi;L. Pentericci;L. Guaita;B. Ribeiro;M. Castellano;D. Schaerer;N. Hathi;B. Lemaux;A. Grazian;O. Fèvre;B. Garilli;D. Maccagni;R. Amorín;S. Bardelli;P. Cassata;A. Fontana;A. Koekemoer;V. Brun;L. Tasca;R. Thomas;E. Vanzella;G. Zamorani;E. Zucca
确定逃离高红移星系的莱曼连续体（LyC）光子的平均比例对于理解z>6宇宙中的再电离如何进行至关重要。我们想要测量来自钱德拉深场南（CDFS）和COSMOS场的样品源的LyC信号，其中超深VIMOS光谱和多波长哈勃太空望远镜（HST）成像可用。
我们从VIMOS超深巡天（VUDS）数据库中选取了46个星系（$z\sim 4$）的样本，使得VUDS光谱包含LyC部分的光谱，即静息帧范围$880-910\AA$。利用HST成像的优势，我们采用了仔细的清洁程序，并排除了所有显示附近不同颜色团块的源，这些团块可能是低红移的闯入者。在这个过程之后，样本减少到33个星系。我们测量了所有单个源的电离通量（LyC在$895\AA$）和非电离辐射（$\sim 1500 \AA$）之间的比率。我们还得到了所有源的归一化叠加谱。假设内在平均值$L_{\nu}(1470)/L_{\nu}(895)$为3，我们估计个体和平均相对逃逸分数。我们没有检测到来自任何单个源的电离辐射，尽管我们确定了一个可能的LyC发射器具有非常高的Ly $\alpha$等效宽度（EW）。从叠加光谱和假设样品的平均透过率，我们测量相对逃逸分数$f_{esc}^{rel}=0.09\pm0.04$。我们还寻找LyC通量的极限与源性质之间的相关性，并发现LyC通量与ly$\alpha$发射线的EW之间的初步相关性。
我们的结果表明，$V=25-26$恒星形成星系在z $\sim$ 4发射的LyC通量最多是非常温和的，与先前基于宽带和窄带成像的研究的上限一致。
Determining the average fraction of Lyman continuum (LyC) photons escaping high redshift galaxies is essential for understanding how reionization proceeded in the z>6 Universe. We want to measure the LyC signal from a sample of sources in the Chandra Deep Field South (CDFS) and COSMOS fields for which ultra-deep VIMOS spectroscopy as well as multi-wavelength Hubble Space Telescope (HST) imaging are available.
We select a sample of 46 galaxies at $z\sim 4$ from the VIMOS Ultra Deep Survey (VUDS) database, such that the VUDS spectra contain the LyC part of the spectra, that is, the rest-frame range $880-910\AA$. Taking advantage of the HST imaging, we apply a careful cleaning procedure and reject all the sources showing nearby clumps with different colours, that could potentially be lower-redshift interlopers. After this procedure, the sample is reduced to 33 galaxies. We measure the ratio between ionizing flux (LyC at $895\AA$) and non-ionizing emission (at $\sim 1500 \AA$) for all individual sources. We also produce a normalized stacked spectrum of all sources. Assuming an intrinsic average $L_{\nu}(1470)/L_{\nu}(895)$ of 3, we estimate the individual and average relative escape fraction. We do not detect ionizing radiation from any individual source, although we identify a possible LyC emitter with very high Ly$\alpha$ equivalent width (EW). From the stacked spectrum and assuming a mean transmissivity for the sample, we measure a relative escape fraction $f_{esc}^{rel}=0.09\pm0.04$. We also look for correlations between the limits in the LyC flux and source properties and find a tentative correlation between LyC flux and the EW of the Ly$\alpha$ emission line.
Our results imply that the LyC flux emitted by $V=25-26$ star-forming galaxies at z$\sim$4 is at most very modest, in agreement with previous upper limits from studies based on broad and narrow band imaging.