A search for z= 7.3 Lyα emitters behind gravitationally lensing clusters
A search for z= 7.3 Lyα emitters behind gravitationally lensing clusters
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搜索引力透镜簇后面的 z= 7.3 Lyα 发射器
DOI：
10.1111/j.1365-2966.2012.21091.x
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发表时间：
2012
影响因子：
4.8
通讯作者：
K. Ota
中科院分区：
文献类型：
--
作者：
K. Abe J. Kameda;M. Miura;Y. Obayashi;T. Kajita;K. Okumura;竹内 努;K. Ota
利用Subaru望远镜Suprime-Cam和窄带滤光片NB 1006（λ c = 1005 nm，半高宽约21 nm）对两个引力透镜星系团阿贝尔2390和CL 0024背后的z= 7.3的Lyα发射体（LAEs）进行了探测。Suprime-Cam的全耗尽CCD对λ 1 μm处的z λ 7 Lyα发射敏感，结合透镜团的放大作用，可能成为探测微弱远距离LAE的有力工具。利用哈勃太空望远镜和斯皮策太空望远镜拍摄的NB 1006和深光学到中红外图像，我们研究了星团后面是否存在与z= 7.3 LAEs颜色一致的物体。我们无法探测到任何非透镜Lyα线通量极限F Lyα = 6.9× 10− 18 erg s− 1 cm− 2的LAE。利用文献中的几种z= 7 Lyα光度函数（LF），估算并比较了8 m级地基望远镜在透镜巡天和空白视场巡天观测中z = 7$ LAEs的期望探测数。考虑到LF的陡峭的亮端斜率，当检测器视场（FOV）与大质量透镜簇的角范围相当时，成像簇在检测z λ 7 LAE方面比成像空白场更有效。然而，增益预计是适度的，最多为2倍，并且可能更少，这取决于所采用的LF。因此，透镜测量的主要优点仍然是深度的增加，而不一定是探测效率的增加。对于大得多的探测器，透镜效应变得可以忽略不计，并且LAE探测的效率与仪器FOV成比例。我们还研究了先前在阿贝尔2390中探测到的三个z-107 z-dropout星系候选者的NB 1006图像，发现它们都没有在NB 1006中探测到。其中两个与先前研究的预测一致，即它们将处于较低的红移。另一个的光度红移为z = 7.3，如果我们假设它在z= 7.3处，则无透镜的Lyα线通量将非常微弱：F Lyα< 4.4× 10− 18 erg s− 1 cm− 2（1σ上限）或相等的宽度。它的Lyα发射可能会被中性氢所衰减，因为最近的研究表明，莱曼破裂星系中显示出强Lyα发射的比例在z = 7时低于z = 6时。
Abstract We searched for z= 7.3 Lyα emitters (LAEs) behind two gravitationally lensing clusters, Abell 2390 and CL 0024, using the Subaru Telescope Suprime-Cam and a narrow-band filter NB1006 (λ c∼ 1005 nm and full width at half-maximum of about 21 nm). The combination of the fully depleted CCDs of the Suprime-Cam, sensitive to z∼ 7 Lyα emission at∼ 1 μm, and the magnification by the lensing clusters can be potentially a powerful tool to detect faint distant LAEs. Using the NB1006 and deep optical to mid-infrared images of the clusters taken with the Hubble Space Telescope and Spitzer Space Telescope, we investigated if there exist objects consistent with the colour of z= 7.3 LAEs behind the clusters. We could not detect any LAEs to the unlensed Lyα line flux limit of F Lyα≃ 6.9× 10− 18 erg s− 1 cm− 2. Using several z= 7 Lyα luminosity functions (LFs) from the literature, we estimated and compared the expected detection numbers of z∼ 7$ LAEs in lensing and blank field surveys in the case of using an 8-m class ground-based telescope. Given the steep bright-end slope of the LFs, when the detector field of view (FOV) is comparable to the angular extent of a massive lensing cluster, imaging cluster (s) is (are) more efficient in detecting z∼ 7 LAEs than imaging a blank field. However, the gain is expected to be modest, a factor of 2 at most and likely much less depending on the adopted LFs. The main advantage of lensing survey, therefore, remains the gain in depth and not necessarily in detection efficiency. For much larger detectors, the lensing effect becomes negligible and the efficiency of LAE detection is proportional to the instrumental FOV. We also investigated the NB1006 images of the three z∼ 7 z-dropout galaxy candidates previously detected in Abell 2390 and found that none of them is detected in NB1006. Two of them are consistent with the predictions from previous studies that they would be at lower redshifts. The other one has a photometric redshift of z≃ 7.3, and if we assume that it is at z= 7.3, the unlensed Lyα line flux would be very faint: F Lyα< 4.4× 10− 18 erg s− 1 cm− 2 (1σ upper limit) or equivalent width of Å. Its Lyα emission might be attenuated by neutral hydrogen, as recent studies show that the fraction of Lyman break galaxies displaying strong Lyα emission is lower at z∼ 7 than at z≲ 6.