Microlensing Optical Depth and Event Rate toward the Galactic Bulge from 8 yr of OGLE-IV Observations
Microlensing Optical Depth and Event Rate toward the Galactic Bulge from 8 yr of OGLE-IV Observations
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8 年 OGLE-IV 观测中银河核球的微透镜光学深度和事件率
DOI：
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发表时间：
2019
影响因子：
8.7
通讯作者：
P. Iwanek
中科院分区：
文献类型：
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作者：
P. Mróz;A. Udalski;J. Skowron;M. Szymański;I. Soszyński;Ł. Wyrzykowski;P. Pietrukowicz;S. Kozłowski;R. Poleski;K. Ulaczyk;K. Rybicki;P. Iwanek
观测到的引力微透镜事件的数量和性质取决于恒星和其他紧致物体沿视线的分布和运动学。特别是，对微透镜光学深度和银河凸出的事件率的精确测量，使对银河系竞争模型的严格测试成为可能。先前的估计，基于几百个事件的样本，给出了比银河系模型预期的更大的值，并且很难与银河系结构的其他限制相协调。在这里，我们利用光学引力透镜实验（OGLE）对银河系凸起的长期光度观测，选择了8000个引力微透镜事件的均匀样本。我们创建了银河系凸起的最大和最精确的微透镜光学深度和事件速率图。新的地图缓和了之前的测量和银河系模型之间的紧张关系。它们与早期一些基于明亮恒星的计算一致，并且比基于“全源”微透镜事件样本的其他估计系统地小约30%。这种差异是由对源星群的仔细估计造成的。新的地图与基于银河系贝桑顿模型的预测非常吻合。除了测试银河系模型之外，我们的地图可能还有许多其他应用，例如测量初始质量函数或限制银河系中心的暗物质含量。新地图还将通过修改预期的事件数量，为未来太空微透镜实验的规划提供信息。
The number and properties of observed gravitational microlensing events depend on the distribution and kinematics of stars and other compact objects along the line of sight. In particular, precise measurements of the microlensing optical depth and event rate toward the Galactic bulge enable strict tests of competing models of the Milky Way. Previous estimates, based on samples of up to a few hundred events, gave larger values than expected from the Galactic models and were difficult to reconcile with other constraints on the Galactic structure. Here we used long-term photometric observations of the Galactic bulge by the Optical Gravitational Lensing Experiment (OGLE) to select a homogeneous sample of 8000 gravitational microlensing events. We created the largest and most accurate microlensing optical depth and event rate maps of the Galactic bulge. The new maps ease the tension between the previous measurements and Galactic models. They are consistent with some earlier calculations based on bright stars and are systematically ∼30% smaller than the other estimates based on “all-source” samples of microlensing events. The difference is caused by the careful estimation of the source star population. The new maps agree well with predictions based on the Besançon model of the Galaxy. Apart from testing the Milky Way models, our maps may have numerous other applications, such as the measurement of the initial mass function or constraining the dark matter content in the Milky Way center. The new maps will also inform the planning of future space-based microlensing experiments by revising the expected number of events.