Microlensing Predictions: Impact of Galactic Disc Dynamical Models

30 Oct 2020  ·  Hongjing Yang, Shude Mao, Weicheng Zang, Xiangyu Zhang ·

Galactic model plays an important role in the microlensing field, not only for analyses of individual events but also for statistics of the ensemble of events. However, the Galactic models used in the field varies, and some are unrealistically simplified. Here we tested three Galactic disc dynamic models, the first is a simple standard model that was widely used in this field, whereas the other two are more realistic taking into account the radial dependence of the velocity dispersion, and in the last model, the asymmetric drift. We found that for a typical lens mass $M_L=0.5M_\odot$, the more accurate dynamical models predict $\sim41\%$ or $\sim27\%$ less long-timescale events ($t_{\rm E}>300$ days) and $\sim 1\%$ and $\sim 12\%$ more short-timescale events ($t_{\rm E}<3$ days) than the standard model. Moreover, large Einstein radius ($\theta_{\rm E}>1$ mas) and large microlensing parallax ($\pi_{\rm E}>0.3$) events are expected to be more common. The more advanced models also have an impact on the total microlensing event rate. This result will also to some degree affect the Bayesian analysis of individual events, so we recommend that modelers should be more careful when choosing the Galactic model. Additionally, we find the asymptotic power-law behaviors in both $\theta_{\rm E}$ and $\pi_{\rm E}$ distributions, and we provide a simple model to understand them.

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Astrophysics of Galaxies Earth and Planetary Astrophysics Solar and Stellar Astrophysics