Microlensing Constraints on the Stellar and Planetary Mass Functions

TL;DR

This paper uses microlensing data to analyze the mass functions of stars, brown dwarfs, and free-floating planets, comparing results with other methods and constraining planetary populations.

Contribution

It provides a comprehensive comparison of microlensing mass functions with other measurements and explores implications for free-floating and wide-orbit planets.

Findings

Brown dwarf abundance consistent with local measurements

Constraints on free-floating planets and their relation to bound planets

Implications for planetary populations from debris disks and ALMA observations

Abstract

The mass function (MF) of isolated objects measured by microlensing consists of both a stellar and a planetary component. We compare the microlensing MFs of Gould et al (2022) and Sumi et al (2023) to other measurements of the MF. The abundance of brown dwarfs in the Sumi et al (2023) stellar MF is consistent with measurements from the local solar neighborhood (Kirkpatrick et al 2024). Microlensing free-floating planets ($\mu$FFPs) may may be free-floating or orbit host stars with semimajor axes $a\gtrsim 10~\mathrm{au}$ and therefore can constrain the populations of both free-floating planetary-mass objects and wide-orbit planets. Comparisons to radial velocity and direct imaging planet populations suggest that either most of the $\mu$FFP population with masses $>1~M_{\rm Jup}$ is bound to hosts more massive than M dwarfs or some fraction of the observed bound population actually comes from the low-mass tail of the stellar population. The $\mu$FFP population also places strong constraints on planets inferred from debris disks and gaps in protoplanetary disks observed by ALMA.