Microlensing Constraints on the Stellar and Planetary Mass Functions

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.