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Although a high fraction of quasars is predicted to be gravitationally lensed at high redshift comma only one z>5 lensed quasar has been discovered to date (J0439+1634 at z=6.5). Recently we identified a promising candidate of a lensed quasar at z=5.07 comma J0025-0145 comma which would be the second lensed quasar at z>5 if confirmed. A number of observational evidences strongly suggest J0025-0145 being lensed comma including (1) the existence of a foreground lens galaxy comma (2) the ground-based image is extended and is well-fitted by a lensing model comma and (3) the SMBH mass implies an exceptionally high super-Eddington accretion ratio comma which can be explained by lensing magnification. The characteristics of J0025-0145 strongly resemble those of J0439+1634. Our model suggests that J0025-0145 is a compact lens (image separation virgul0.1d_comma) with large magnification (virgul80). HST is needed to confirm the lensing scenario. Because of its high magnification comma J0025-0145 will provide the first chance to study the host galaxy of a faint quasar at z>5 with high S-N and high spatial resolution comma and to probe the SMBH-galaxy co-evolution in a low mass system at high-redshift in great details. We propose ACS-WFC imaging of J0025-0145. We will use F435W to capture the lens galaxy comma and use F606W to measure the lensed quasar images. The proposed observation will be the definitive test of the lensing hypothesis comma and will provide an accurate lensing model which will enable follow-up studies comma especially high S-N JWST and ALMA observations. The proposed observation will be a crucial step towards building a sample of high-redshift lensed quasars comma which is essential to a comprehensive view of high-redshift SMBH population.

尽管理论预测高红移类星体中存在较高比例的引力透镜天体，但截至目前仅发现1颗红移z>5的透镜类星体：红移z=6.5的J0439+1634。近期我们识别出一颗红移z=5.07的透镜类星体候选体J0025-0145，若得到证实，它将成为第二颗红移z>5的透镜类星体。多项观测证据强烈支持J0025-0145为透镜天体，具体包括：(1) 存在前景透镜星系；(2) 地面观测图像呈延展形态，且可通过透镜模型得到良好拟合；(3) 超大质量黑洞（Supermassive Black Hole, SMBH）的质量暗示其拥有极高的超爱丁顿吸积率，该现象可通过透镜放大效应得到合理解释。J0025-0145的观测特征与J0439+1634高度相似。我们的模型显示，J0025-0145属于紧凑透镜系统（图像间距约0.1角秒），且具备约80倍的高放大倍率。需借助哈勃空间望远镜（Hubble Space Telescope, HST）验证该透镜假说。得益于其极高的放大倍率，J0025-0145将为我们提供首次契机：以高信噪比（signal-to-noise, S-N）与高空间分辨率研究红移z>5的暗弱类星体宿主星系，并详细探究高红移低质量系统中超大质量黑洞与星系的共同演化过程。我们申请对J0025-0145开展先进巡天相机广域通道（Advanced Camera for Surveys Wide Field Channel, ACS-WFC）成像观测：使用F435W滤光片拍摄透镜星系，使用F606W滤光片测量透镜类星体的多幅图像。本次申请的观测将最终验证该透镜假说，并得到精确的透镜模型，为后续研究铺平道路，尤其是开展高信噪比的詹姆斯·韦布空间望远镜（James Webb Space Telescope, JWST）与阿塔卡马大型毫米波/亚毫米波阵列（Atacama Large Millimeter/submillimeter Array, ALMA）观测。本次申请的观测将为构建高红移透镜类星体样本迈出关键一步，而该样本对于全面认知高红移超大质量黑洞族群具有至关重要的意义。