VVV Survey Microlensing: the Galactic Latitude Dependence

TL;DR

This study analyzes the distribution of microlensing events along the Galactic minor axis using VVV survey data, revealing a strong latitude dependence and a flattened event distribution.

Contribution

It provides the first detailed analysis of microlensing event distribution as a function of Galactic latitude, using near-IR data from the VVV survey.

Findings

Number of microlensing events increases sharply towards the Galactic center.

The event distribution is flattened with an axial ratio of approximately 1.5.

The mean timescale of events is shorter near the Galactic plane.

Abstract

We search for microlensing events in fields along the Galactic minor axis, ranging from the Galactic center to -3.7<b< 3.9 deg., using the VVV survey near-IR photometry. The new search is made across VVV tiles b291, b305, b319, b347, b361 and b375, 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 of 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 b333), 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, number that increases rapidly towards the Galactic center by one order of magnitude from |b|=2 deg. to b=0 deg. with a much steeper gradient than with Galactic longitude. The microlensing event population shows a flattened distribution (axial ratio b/a \approx 1.5). The final sample shows a shorter mean timescale distribution than the Galactic plane sample for both, the complete population and RC stars.