标题： 欧几里得预备工作。 第四十九。 利用观测颜色选择活动星系核 显示英文标题

标题： Euclid preparation. XLIX. Selecting active galactic nuclei using observed colours

摘要： 欧几里得任务将使用两种光学和近红外光谱-光度仪器覆盖超过14000个$deg^{2}$，并有望探测到大约一千万个活动星系核（AGN）。 这一独特的数据集将在很大程度上影响我们对星系演化和AGN的理解。 在这项工作中，我们基于欧几里得测光数据或包括辅助测光观测（如鲁宾时空遗产巡天（LSST）的数据以及斯皮策/IRAC已有的观测数据）来确定最佳的AGN颜色选择标准。 分析针对的是未被遮蔽的AGN、被遮蔽的AGN以及复合型（AGN和恒星形成）对象。 我们利用红外选目标的所有红移（SPRITZ）的光谱-光度实现来创建模拟目录，模仿欧几里得宽视场巡天（EWS）和欧几里得深视场巡天（EDS）。 利用这些目录，我们估计了最佳的颜色选择方案，最大化完整性和纯度的调和平均值（F1）。 在两个欧几里得巡天中选择未被遮蔽的AGN仅需欧几里得测光数据即可达到F1=0.22-0.23，如果限制z>0.7，则可以增加至F1=0.43-0.38。 一旦考虑鲁宾/LSST滤镜（u、g、r或z滤镜的组合），这种选择会得到改善，分别使EDS和EWS的F1达到0.84和0.86。 将一个欧几里得颜色与[3.6]-[4.5]颜色相结合（这仅在EDS中可能），可得到F1分数为0.59，比仅使用欧几里得滤镜的结果有所改进，但不如结合欧几里得和LSST的选择。 对于复合型（在8-40$\mu m$范围内$f_{{\rm AGN}}$=0.05-0.65）和被遮蔽的AGN的选择具有挑战性，即使包括辅助数据，F1也小于0.3。 这是由于这些AGN和恒星形成星系在0.3-5$\mu m$波长范围内的宽带谱能量分布相似。 显示英文摘要

摘要： Euclid will cover over 14000 $deg^{2}$ with two optical and near-infrared spectro-photometric instruments, and is expected to detect around ten million active galactic nuclei (AGN). This unique data set will make a considerable impact on our understanding of galaxy evolution and AGN. In this work we identify the best colour selection criteria for AGN, based only on Euclid photometry or including ancillary photometric observations, such as the data that will be available with the Rubin legacy survey of space and time (LSST) and observations already available from Spitzer/IRAC. The analysis is performed for unobscured AGN, obscured AGN, and composite (AGN and star-forming) objects. We make use of the spectro-photometric realisations of infrared-selected targets at all-z (SPRITZ) to create mock catalogues mimicking both the Euclid Wide Survey (EWS) and the Euclid Deep Survey (EDS). Using these catalogues we estimate the best colour selection, maximising the harmonic mean (F1) of completeness and purity. The selection of unobscured AGN in both Euclid surveys is possible with Euclid photometry alone with F1=0.22-0.23, which can increase to F1=0.43-0.38 if we limit at z>0.7. Such selection is improved once the Rubin/LSST filters (a combination of the u, g, r, or z filters) are considered, reaching F1=0.84 and 0.86 for the EDS and EWS, respectively. The combination of a Euclid colour with the [3.6]-[4.5] colour, which is possible only in the EDS, results in an F1-score of 0.59, improving the results using only Euclid filters, but worse than the selection combining Euclid and LSST. The selection of composite ($f_{{\rm AGN}}$=0.05-0.65 at 8-40 $\mu m$) and obscured AGN is challenging, with F1<0.3 even when including ancillary data. This is driven by the similarities between the broad-band spectral energy distribution of these AGN and star-forming galaxies in the wavelength range 0.3-5 $\mu m$.