New Self-lensing Models of the Small Magellanic Cloud: Can Gravitational Microlensing Detect Extragalactic Exoplanets?

TL;DR

This study models the stellar density of the Small Magellanic Cloud using Cepheids and RR Lyrae stars to estimate microlensing optical depth, suggesting future surveys could detect extragalactic exoplanets if observing strategies are optimized.

Contribution

It introduces detailed 3D stellar distribution models of the SMC for microlensing predictions and assesses the potential for detecting extragalactic exoplanets with LSST.

Findings

Models match observed microlensing optical depth.

LSST could detect up to a few dozen microlensing events annually.

Potential to discover extragalactic exoplanets with optimized strategies.

Abstract

We use three-dimensional distributions of classical Cepheids and RR~Lyrae stars in the Small Magellanic Cloud (SMC) to model the stellar density distribution of a young and old stellar population in that galaxy. We use these models to estimate the microlensing self-lensing optical depth to the SMC, which is in excellent agreement with the observations. Our models are consistent with the total stellar mass of the SMC of about 1.0 x 10^9 MSun under the assumption that all microlensing events toward this galaxy are caused by self-lensing. We also calculate the expected event rates and estimate that future large-scale surveys, like the Large Synoptic Survey Telescope (LSST), will be able to detect up to a few dozen microlensing events in the SMC annually. If the planet frequency in the SMC is similar to that in the Milky Way, a few extragalactic planets can be detected over the course of the LSST survey, provided significant changes in the SMC observing strategy are devised. A relatively small investment of LSST resources can give us a unique probe of the population of extragalactic exoplanets.