Pathway to the Galactic Distribution of Planets: Combined Spitzer and Ground-Based Microlens Parallax Measurements of 21 Single-Lens Events

TL;DR

This study combines microlens parallax data from Spitzer and ground-based observations for 21 isolated lenses toward the Galactic bulge to estimate their distances and explore the Galactic distribution of planets, paving the way for future comparative analyses.

Contribution

It provides a method to derive precise lens distances using combined parallax measurements and a Galactic kinematic model, establishing a foundation for future Galactic planet distribution studies.

Findings

Derived small-error distance estimates for 21 lenses.

Established a cumulative distribution of lens distances in the Galaxy.

Set the stage for future comparisons with planetary detections.

Abstract

We present microlens parallax measurements for 21 (apparently) isolated lenses observed toward the Galactic bulge that were imaged simultaneously from Earth and Spitzer, which was ~1 AU West of Earth in projection. We combine these measurements with a kinematic model of the Galaxy to derive distance estimates for each lens, with error bars that are small compared to the Sun's Galactocentric distance. The ensemble therefore yields a well-defined cumulative distribution of lens distances. In principle it is possible to compare this distribution against a set of planets detected in the same experiment in order to measure the Galactic distribution of planets. Since these Spitzer observations yielded only one planet, this is not yet possible in practice. However, it will become possible as larger samples are accumulated.