Microlensing Events in the Galactic Plane with the Zwicky Transient Facility

Antonio Rodriguez  ✧  The California Institute of Technology (Caltech), CA, USA

The majority of previous efforts to search for gravitational microlensing events have been concentrated towards high-density fields such as the Galactic bulge, avoiding the Galactic plane. Microlensing events in the Galactic plane have the advantage of better constrained relative proper motions and therefore better constrained lens mass estimates, at the expense of a lower optical depth compared to events towards the Galactic bulge. We use the Zwicky Transient Facility (ZTF) Data Release 5 (DR5) compiled from 2018-2021 to survey the Galactic plane. We find a total of 60 candidate microlensing events including three that show a strong microlensing parallax effect. The number of events traces Galactic structure, decreasing exponentially as a function Galactic longitude. On average, we find Einstein timescales of microlensing events to be about three times as long towards the Galactic plane (60 days) compared to those towards the Galactic bulge (20 days). Our results demonstrate that microlensing towards the Galactic plane shows strong promise for characterization of dark objects within the galaxy that no other technique can do at the present time.