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Comparison of microlensing planet distribution with a Galactic model

Presentation #218.06 in the session “Exoplanet Populations: Masses and Microlensing”.

Published onJan 11, 2021
Comparison of microlensing planet distribution with a Galactic model

Gravitational microlensing is almost the only technique that can study the Galactic distribution of planets as a function of distance from the Galactic center. However, the distance can be uniquely determined only when more than two of the three mass-distance relations (the angular Einstein radius, the microlens parallax, and the lens flux) are measured. Out of the three mass-distance relations, the angular Einstein radius is commonly measured for planetary microlensing events, and we might extract some information about the mass or distance from it. In this study, we compare the 30 angular Einstein radius measurements from the planetary sample by Suzuki et al. (2016) with a Galactic model that is commonly used in microlensing analysis. We find a statistically significant excess of the angular Einstein radius values compared to the expectation from the Galactic model when the Einstein radius crossing time tE > ~60 days. This excess might be interpreted as the first certain evidence that planets are less common in the bulge compared to the disk. Another interpretation is that the Galactic model used is too simple. We update our model so that it becomes consistent with the velocity measurements by Gaia to find that the excess still remains. In the talk, I report the detail of the comparison and current status of our analysis.

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