The frequency of snowline-region planets from four-years of OGLE-MOA-Wise second-generation microlensing

TL;DR

This study analyzes four years of microlensing data from OGLE, MOA, and Wise surveys, revealing that over half of the stars host snowline planets, with Neptunes being significantly more common than Jupiters, and identifying distinct companion populations.

Contribution

It provides the first comprehensive statistical estimate of snowline planet frequency from a second-generation microlensing survey, highlighting the prevalence of low-mass planets and companion population distinctions.

Findings

Over 55% of microlensed stars host snowline planets.

Neptune-mass planets are about 10 times more common than Jupiter-mass planets.

The companion-to-host mass ratio distribution shows a deficit at q~10^{-2}, indicating two distinct populations.

Abstract

We present a statistical analysis of the first four seasons from a "second-generation" microlensing survey for extrasolar planets, consisting of near-continuous time coverage of 8 deg$^2$ of the Galactic bulge by the OGLE, MOA, and Wise microlensing surveys. During this period, 224 microlensing events were observed by all three groups. Over 12% of the events showed a deviation from single-lens microlensing, and for $\sim$1/3 of those the anomaly is likely caused by a planetary companion. For each of the 224 events we have performed numerical ray-tracing simulations to calculate the detection efficiency of possible companions as a function of companion-to-host mass ratio and separation. Accounting for the detection efficiency, we find that $55^{+34}_{-22}\%$ of microlensed stars host a snowline planet. Moreover, we find that Neptunes-mass planets are $\sim10$ times more common than Jupiter-mass planets. The companion-to-host mass ratio distribution shows a deficit at $q\sim10^{-2}$, separating the distribution into two companion populations, analogous to the stellar-companion and planet populations, seen in radial-velocity surveys around solar-like stars. Our survey, however, which probes mainly lower-mass stars, suggests a minimum in the distribution in the super-Jupiter mass range, and a relatively high occurrence of brown-dwarf companions.