VVV Survey Microlensing: The Galactic Latitude Dependence

Abstract

We search for microlensing events in fields along the Galactic minor axis, ranging from the Galactic center to −3.°7 <  b  < 3.°9 using the VISTA Variables in the Via Láctea (VVV) survey near-IR photometry. The new search is made across VVV tiles b 291, b 305, b 319, b 347, b 361, and b 375, covering a total area of about 11.5 deg 2 . We find a total of N  = 238 new microlensing events in this new area, N  = 74, which are classified as bulge red clump (RC) giant sources. Combining them with N  = 122 events that we had previously reported in the Galactic center (VVV tile b 333), allows us to study the latitude distribution of the microlensing events reaching the Galactic plane at b  = 0 0 for the first time. We find a very strong dependence of the number of microlensing events with Galactic latitude, a number that increases rapidly toward the Galactic center by one order of magnitude from ° to b  = 0° with a much steeper gradient than with Galactic longitude. The microlensing event population shows a flattened distribution (axial ratio b / a ≈ 1.5). The final sample shows a shorter mean timescale distribution than the Galactic plane sample for both the complete population and RC stars.