VVV Survey Microlensing: the Galactic Longitude Dependence

TL;DR

This study analyzes microlensing events in the Galactic bulge using near-infrared data from the VVV Survey, revealing a smooth increase in event numbers towards the Galactic center and a slight asymmetry related to the Galactic bar's inclination.

Contribution

It provides the first detailed analysis of the longitude dependence of microlensing events in the Galactic bulge using near-IR data from the VVV Survey, highlighting asymmetries and timescale distributions.

Findings

Number of microlensing events increases towards the Galactic center.

Detected a slight asymmetry with more events at negative longitudes.

Timescale distribution peaks at around 17.4 days for the complete sample.

Abstract

We completed the search for microlensing events in the zero latitude area of the Galactic bulge using the VVV Survey near-IR data obtained between 2010 and 2015. We have now a total sample of N = 630 events Using the near-IR Color-Magnitude Diagram we selected the Red Clump sources to analyze the longitude dependence of microlensing across the central region of the Galactic plane. The events show a homogeneous distribution, smoothly increasing in numbers towards the Galactic centre, as predicted by different models. We find a slight asymmetry, with a larger number of events toward negative longitudes than positive longitudes. This asymmetry is seen both in the complete sample and the subsample of red clump giant sources, and it is possibly related with the inclination of the bar along the line of sight. The timescale distribution is fairly symmetric with a peak in 17.4 $\pm$ 1.0 days for the complete sample (N = 630 events), and 20.7 $\pm$ 1.0 days for the Red Clump stars (N = 291 events), in agreement with previous results.