VVV survey microlensing: candidate events with source in the far disk

TL;DR

This study identifies potential microlensing events with sources in the far disk of the Galaxy using the VVV survey, revealing a significant subset with longer timescales that could impact future IR microlensing observations.

Contribution

It introduces a method to identify far-disk microlensing sources in the VVV survey and estimates their prevalence and characteristics.

Findings

Approximately 11% of events have candidate far-disk sources.

Far-disk source events tend to have longer timescales (~49 days).

The results inform future IR microlensing surveys like the Roman Space Telescope.

Abstract

The VVV microlensing search has recently surveyed the region of the Galactic plane at b=0 within -10.00 < l < 10.44 deg. in the near-infrared (IR), discovering hundreds of microlensing events. In this paper we explore the microlensing events with background sources that might be located in the far disk of the Galaxy, beyond the bulge. We discuss the possible configurations for the microlensing lenses and sources located at different places within the Galactic plane. Then we search for these events using the local red clump centroids of the VVV near-IR color-magnitude diagrams. According to the estimated distances and proper motions, N=20 events may have sources located in the far disk. The candidates for far-disk sources show on average longer timescales (tE= 49.3 +- 7.9 days) than the mean of the timescale distribution for the bulge red clump sources (tE= 36.4 +- 1.1 days). We conclude that the population of microlensing events in the region -10.00 < l < 10.44, -0.46 < b < 0.65 deg. contains a non-negligible number of events with candidate far-disk sources (~ 11 %). Our results are relevant in view of the future microlensing plans with the Roman Space Telescope (formerly WFIRST) in the near-IR.