Can gravitational microlensing detect extragalactic exoplanets? Self-lensing models of the Small Magellanic Cloud

摘要

We use three-dimensional distributions of classical Cepheids and RR Lyraestars in the Small Magellanic Cloud (SMC) to model the stellar densitydistribution of a young and old stellar population in that galaxy. We use thesemodels to estimate the microlensing self-lensing optical depth to the SMC,which is in excellent agreement with the observations. Thus, we estimate thetotal stellar mass of the SMC of about 1.0 x 10^9 MSun under assumption thatall microlensing events toward this galaxy are caused by self-lensing. We alsocalculate the expected event rates and estimate that future large-scalesurveys, like the Large Synoptic Survey Telescope (LSST), will be able todetect up to a few dozen microlensing events in the SMC annually. If the planetfrequency in the SMC is similar to that in the Milky Way, a few extragalacticplanets can be detected over the course of the LSST survey, providedsignificant changes in the SMC observing strategy are devised. A relativelysmall investment of LSST resources can give us a unique probe of the populationof extragalactic exoplanets.