用盖亚研究河外点源的纯天体测量选择
A study of purely astrometric selection of extragalactic point sources with Gaia
摘要：
选择河外点源，如类星体，往往受到显着的选择效应，导致现有的样本有相当复杂的选择功能。我们探讨是否一个纯粹的天体测量选择河外点源，如类星体，是可行的与正在进行的盖亚任务。这样的选择将是有趣的，因为它在目标的颜色方面是无偏的，因此也允许选择恒星序列中的颜色。我们已经分析了总共18个代表性的天空区域，使用GUMS，为欧空局盖亚任务准备的模拟器，无论是在范围内的$12\le G \le 20$马格和$12\le G \le 18$马格。对于每个区域，我们确定的密度显然是固定的恒星源，即盖亚不能测量一个显着的自行的来源。的密度与河外点源，如类星体的密度，以建立一个纯粹的天体测量的选择是可行的天体方向。当瞄准银纬$|b| \ge 30^\mathrm{o}$的区域时，类星体与表面上静止的恒星的比例超过50%，而当朝向两极观测时，类星体的比例上升到大约$\sim80$ %。我们表明，在大约20年的时间里，拟议中的盖亚后续任务的自行将大大改善所有纬度的这些结果。仅从零自行探测类星体，不受任何光谱假设的影响，可能会导致发现新类型的类星体或新类别的河外点源。
英文摘要：
Selection of extragalactic point sources, e.g. QSOs, is often hampered by significant selection effects causing existing samples to have rather complex selection functions. We explore whether a purely astrometric selection of extragalactic point sources, e.g. QSOs, is feasible with the ongoing Gaia mission. Such a selection would be interesting as it would be unbiased in terms of colours of the targets and hence would allow selection also with colours in the stellar sequence. We have analyzed a total of 18 representative regions of the sky by using GUMS, the simulator prepared for ESAs Gaia mission, both in the range of $12\le G \le 20$ mag and $12\le G \le 18$ mag. For each region we determine the density of apparently stationary stellar sources, i.e. sources for which Gaia cannot measure a significant proper motion. The density is contrasted with the density of extragalactic point sources, e.g. QSOs, in order to establish in which celestial directions a pure astrometric selection is feasible. When targeting regions at galactic latitude $|b| \ge 30^\mathrm{o}$ the ratio of QSOs to apparently stationary stars is above 50\% and when observing towards the poles the fraction of QSOs goes up to about $\sim80$\%. We show that the proper motions from the proposed Gaia successor mission in about 20 years would dramatically improve these results at all latitudes. Detection of QSOs solely from zero proper motion, unbiased by any assumptions on spectra, might lead to the discovery of new types of QSOs or new classes of extragalactic point sources.
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