The Lyman continuum escape fraction of galaxies at z = 3.3 in the VUDS-LBC/COSMOS field
The Lyman continuum escape fraction of galaxies at z = 3.3 in the VUDS-LBC/COSMOS field
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VUDS-LBC/COSMOS 场中 z = 3.3 处星系的莱曼连续逃逸分数
DOI：
10.1051/0004-6361/201526396
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
et al.
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文献类型：
--
作者：
Grazian;A.;et al.
背景从高红移星系逃逸到星际介质的电离莱曼连续通量是理解再电离时代所涉及的物理过程的一个基本量。然而，从观测的角度来看，直接探测高红移的高红移电离光子对于主要位于−~3星系的星系是可行的。目的我们研究了Z~3.3的恒星形成星系样本，以寻找从星系晕中逃逸的莱曼连续谱电离光子的可能的探测。方法我们利用LBT望远镜的主焦相机LBC获得的宇宙场的深紫外光成像，以及VIMOS超深探测获得的光谱红移目录来建立一个包括45个星系的样本，这些星系位于Z~3.3，L>；0.5L∗。我们获得了光谱红移在3.27<；z<；3.40的星系的深部LBC图像(星等极限U~29.7ATS/N=1)。在这些红移中，热波段对非电离1500？静止帧光度进行采样，而U波段对912？莱曼边缘附近的静止帧光谱区域进行采样。它们的通量比与统计剔除视线上星系间介质吸收后的电离逃逸分数有关。结果10个星系的一个小样本明显地显示出>；28%的逃逸分数，但对其性质的详细分析表明，除了U波段的两个边缘探测(S/N~2)外，其他8个星系都最有可能受到靠近高纬目标的低红移入侵者的紫外线通量的污染。来自清洁样品堆积的平均逸出分数被限制在2%以内。这些结果支持高红移、相对明亮(L≥0.5L∗)的恒星形成星系不能单独维持宇宙星际介质在Z~3的电离水平。只有红移较高、亮度较低的恒星形成星系(L(≪L∗))才可能是宇宙再电离的主要贡献者。在高红移的活动星系核群体中，可以发现电离源，寻找较弱的源。
ContextThe ionizing Lyman continuum flux escaping from high-redshift galaxies into the intergalactic medium is a fundamental quantity to understand the physical processes involved in the reionization epoch. However, from an observational point of view, direct detections of HI ionizing photons at high redshifts are feasible for galaxies mainly in the intervalz~ 3−4.AimsWe have investigated a sample of star-forming galaxies atz~ 3.3 to search for possible detections of Lyman continuum ionizing photons escaping from galaxy halos.MethodsWe used deep ultraviolet (UV) imaging in the COSMOS field, obtained with the prime focus camera LBC at the LBT telescope, along with a catalogue of spectroscopic redshifts obtained by the VIMOS Ultra Deep Survey (VUDS) to build a sample of 45 galaxies atz~ 3.3 withL> 0.5L∗. We obtained deep LBC images of galaxies with spectroscopic redshifts in the interval 3.27 <z< 3.40 both in theR- and deepU-bands (magnitude limitU~ 29.7 atS/N= 1). At these redshifts, theR-band samples the non-ionizing 1500 Å rest-frame luminosity and theU-band samples the rest-frame spectral region just short-ward of the Lyman edge at 912 Å. Their flux ratio is related to the ionizing escape fraction after statistical removal of the absorption by the intergalactic medium along the line of sight.ResultsA subsample of ten galaxies apparently shows escape fractions >28%, but a detailed analysis of their properties reveals that, with the exception of two marginal detections (S/N~ 2) in theU-band, all the other eight galaxies are most likely contaminated by the UV flux of low-redshift interlopers located close (in angular position) to the high-ztargets. The average escape fraction derived from the stacking of the cleaned sample was constrained tofescrel< 2%. The implied hydrogen photoionization rate is a factor two lower than that needed to keep the intergalactic medium ionized atz~ 3, as observed in the Lyman-αforest of high-zquasar spectra or by the proximity effect.ConclusionsThese results support a scenario where high redshift, relatively bright (L≥ 0.5L∗) star-forming galaxies alone are unable to sustain the level of ionization observed in the cosmic intergalactic medium atz~ 3. Star-forming galaxies at higher redshift and at fainter luminosities (L≪L∗) can only be major contributors to the reionization of the Universe if their physical properties are subject to rapid changes fromz~ 3 toz~ 6–10. Alternatively, ionizing sources could be discovered looking for fainter sources among the active galactic nuclei population at high redshift.
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