千度巡天的第四次数据发布：1000平方度以上的ugri成像和九波段光学-红外测光
The fourth data release of the Kilo-Degree Survey: ugri imaging and nine-band optical-IR photometry over 1000 square degrees
摘要：
Kilo-Degree Survey（KiDS）是一项正在进行的光学宽视场成像调查，使用VLT巡天望远镜上的OmegaCAM相机，专门用于测量星系和大尺度结构的弱引力透镜。完成后，它将包括1350平方度的四个过滤器（ugri）成像。在这里，我们介绍了第四次公开数据发布，该数据发布覆盖的天空面积比第三次数据发布覆盖的天空面积增加了一倍多。我们还包括孔径匹配ZYJHKs测光从我们的合作伙伴海盗调查的VISTA望远镜的测光目录。我们说明了数据的质量和描述目录的内容。两个专用管道用于产生光学数据。Astro-WISE信息系统用于产生四个测量波段的共同添加图像，而使用theli管道对r波段图像进行单独缩减，以提供适合于核心弱透镜科学案例的源目录。使用最新版本的管道，对本次数据发布的所有数据进行了重新简化。维京测光是通过对来自VISTA爪印的维京数据进行再还原，对theli源进行强制测光而获得的。详细描述了相对于早期版本对管道的修改。测光校准到盖亚DR 2 G波段使用恒星轨迹回归。在此数据发布中，共有1006平方度的调查瓦片与堆叠的ugri图像，伴随着权重图，面具和单波段源列表。我们还提供了一个多波段目录的基础上，r-波段检测，包括均匀化测光和光度红移，为整个数据集。平均极限星等（2”孔径中的5 σ）分别为24.23、25.12、25.02、23.68，平均r波段视宁度为0.70”。
英文摘要：
The Kilo-Degree Survey (KiDS) is an ongoing optical wide-field imaging survey with the OmegaCAM camera at the VLT Survey Telescope, specifically designed for measuring weak gravitational lensing by galaxies and large-scale structure. When completed it will consist of 1350 square degrees imaged in four filters (ugri). Here we present the fourth public data release which more than doubles the area of sky covered by data release 3. We also include aperture-matched ZYJHKs photometry from our partner VIKING survey on the VISTA telescope in the photometry catalogue. We illustrate the data quality and describe the catalogue content. Two dedicated pipelines are used for the production of the optical data. The Astro-WISE information system is used for the production of co-added images in the four survey bands, while a separate reduction of the r-band images using the theli pipeline is used to provide a source catalogue suitable for the core weak lensing science case. All data have been re-reduced for this data release using the latest versions of the pipelines. The VIKING photometry is obtained as forced photometry on the theli sources, using a re-reduction of the VIKING data that starts from the VISTA pawprints. Modifications to the pipelines with respect to earlier releases are described in detail. The photometry is calibrated to the Gaia DR2 G band using stellar locus regression. In this data release a total of 1006 square-degree survey tiles with stacked ugri images are made available, accompanied by weight maps, masks, and single-band source lists. We also provide a multi-band catalogue based on r-band detections, including homogenized photometry and photometric redshifts, for the whole dataset. Mean limiting magnitudes (5 sigma in a 2" aperture) are 24.23, 25.12, 25.02, 23.68 in ugri, respectively, and the mean r-band seeing is 0.70".
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