Subaru/Suprime-Cam窄带成像探测z~3恒星形成星系的莱曼连续谱
Detections of Lyman Continuum from Star-forming Galaxies at z~3 Through Subaru/Suprime-Cam Narrow-band Imaging
摘要：
了解来自年轻恒星形成星系的电离光子的数量对于理解再电离过程特别重要。在这里，我们报告了斯巴鲁/Suprime-Cam深度成像观测的SSA 22原星系团区域在z=3.09的初步结果，使用一个特殊的窄带滤波器，以最佳跟踪莱曼连续区（LyC）从星系在z~3。Suprime-Cam独特的宽视场使我们能够搜索来自198个星系（73个Lyman break星系（LBG）和125个Ly-alpha发射体（LAE））的电离光子，光谱测量的红移z~3.1。我们从7个LBG以及10个LAE候选者中检测到LyC。一些检测到的星系显示出显着的空间偏移的LyC从非电离紫外线辐射。对于一些LBG的观测到的非电离紫外线LyC通量密度比小于预期的值从人口合成模型与标准的萨尔彼得初始质量函数（IMF）与中度尘埃衰减（这是建议从观测到的紫外线斜率），即使我们假设非常透明的IGM沿这些对象的视线。这意味着一个本质上更蓝的光谱能量分布，例如，由一个头重脚轻的IMF，这些LBG。观测到的7个LBG的非电离UV与LyC的通量密度比范围为2.4至23.8，中位数为6.6。如果它们真的在z~3.1处，则所检测到的LAE的观测通量密度比甚至小于LBG。我们发现，检测到的LBG的通量密度比的中值表明，它们的逃逸分数很可能高于4%，如果LyC逃逸是各向同性的。结果表明，z~3处原星系团中的某些LBG的逃逸分数明显高于以往研究的z~1处星系的逃逸分数。
英文摘要：
Knowing the amount of ionizing photons from young star-forming galaxies is of particular importance to understanding the reionization process. Here we report initial results of Subaru/Suprime-Cam deep imaging observation of the SSA22 proto-cluster region at z=3.09, using a special narrow-band filter to optimally trace Lyman continuum (LyC) from galaxies at z~3. The unique wide field-of-view of Suprime-Cam enabled us to search for ionizing photons from 198 galaxies (73 Lyman break galaxies (LBGs) and 125 Ly-alpha emitters (LAEs)) with spectroscopically measured redshifts z~3.1. We detected LyC from 7 LBGs, as well as from 10 LAE candidates. Some of the detected galaxies show significant spatial offsets of LyC from non-ionizing UV emission. For some LBGs the observed non-ionizing UV to LyC flux density ratios are smaller than values expected from population synthesis models with a standard Salpeter initial mass function (IMF) with moderate dust attenuation (which is suggested from the observed UV slopes), even if we assume very transparent IGM along the sightlines of these objects. This implies an intrinsically bluer spectral energy distribution, e.g, that produced by a top-heavy IMF, for these LBGs. The observed flux desity ratios of non-ionizing UV to LyC of 7 detected LBGs range from 2.4 to 23.8 and the median is 6.6. The observed flux density ratios of the detected LAEs are even smaller than LBGs, if they are truly at z~3.1. We find that the median value of the flux density ratio for the deteced LBGs suggest that their escape fractions is likely to be higher than 4%, if the LyC escape is isotropic. The results imply that some of the LBGs in the proto-cluster at z~3 have the escape fraction significantly higher than that of galaxies (in a general field) at z~1 studied previously.
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