OGLE-III Microlensing Events and the Structure of the Galactic Bulge

TL;DR

This paper presents the largest catalog of microlensing events from OGLE-III, enabling detailed analysis of the Galactic bulge's structure, kinematics, and mass distribution, with implications for understanding the Milky Way's central regions.

Contribution

The study introduces a comprehensive microlensing event catalog using machine learning, and provides new insights into the Galactic bar's orientation and the distribution of lenses in the bulge.

Findings

Good agreement with models of the Galactic bar

Detection of bar tilt signature in microlensing data

Asymmetry in time-scales suggests a different bar orientation or width

Abstract

We present and study the largest and the most comprehensive catalog of microlensing events ever constructed. The sample of standard microlensing events comprises 3718 unique events from years 2001--2009, with 1409 not detected before in real-time by the Early Warning System of the Optical Gravitational Lensing Experiment (OGLE). The search pipeline makes use of Machine Learning algorithms in order to help find rare phenomena among 150 million objects and derive the detection efficiency. Applications of the catalog can be numerous, from analyzing individual events to large statistical studies for the Galactic mass and kinematics distributions and planetary abundances. We derive the maps of the mean Einstein ring crossing time of events spanning 31 sq. deg. toward of the Galactic Center and compare the observed distributions with the most recent models. We find good agreement within the observed region and we see the signature of the tilt of the bar in the microlensing data. However, the asymmetry of the mean time-scales seems to rise more steeply than predictions, indicating either a somewhat different orientation of the bar or a larger bar width. The map for the events with sources in the Galactic bulge shows a dependence of the mean time-scale on the Galactic latitude, signaling an increasing contribution from disk lenses closer to the plane, related with the height of the disk. Our data present a perfect set for comparing and enhancing new models of the central parts of the Milky Way and creating the 3D picture of the Galaxy.