The Galactic Dynamics of Free-Floating Planets: From Ejection Kicks to Microlensing
Abstract
Free-floating planets (FFPs) may retain dynamical signatures of the mechanisms that eject them from their host systems. We integrate 106 collisionless FFP test particles for 108~yr in a static, phenomenological Galactic potential, comparing a mass-independent kick model with a mass-coupled prescription (σCB∝ M−0.15, vPL∝ M−0.5) against a matched no-kick control. The imposed mass dependence is recovered at injection, with the combined-channel median coupled kick decreasing from $10.716$ to 0.708 km s−1 across five mass bins---a factor of ∼15.1. A mass-dependent trend remains visible after $100$~Myr of Galactic propagation in the matched kicked-versus-control displacement, whose median decreases from $0.7001$ to $0.0539$~kpc across the same bins. The remaining numerical distinction is concentrated in this mass-resolved differential displacement rather than in the bulk phase-space moments: the final velocity dispersions of the null and coupled kicked populations are nearly identical, only a few percent of particles leave the adopted disk region, and the fraction of particles satisfying the formal Galactic-unbound criterion (Ei>0) remains negligible in every diagnostic we report. Comparing each kicked population against its matched no-kick control shows that much of the overall kinematic heating arises from the evolution of the initially warm, nonequilibrium disk rather than from the ejection kick itself, isolating the kick's smaller contribution.
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BibTeX
@misc{sayed2026galactic,
title = {{The Galactic Dynamics of Free-Floating Planets: From Ejection Kicks to Microlensing}},
author = {Zara Sayed and Stefano Profumo and Nolan Smyth},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.21027},
eprint = {2609.21027},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.21027},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The Galactic Dynamics of Free-Floating Planets: From Ejection Kicks to Microlensing
AU - Zara Sayed
AU - Stefano Profumo
AU - Nolan Smyth
PY - 2026
DA - 2026/09/17
PB - arXiv
DO - 10.48550/arxiv.2609.21027
UR - https://arxiv.org/abs/2609.21027
AB - Free-floating planets (FFPs) may retain dynamical signatures of the mechanisms that eject them from their host systems. We integrate 10^6 collisionless FFP test particles for 10^8~yr in a static, phenomenological Galactic potential, comparing a mass-independent kick model with a mass-coupled prescription (σ_CB∝ M^−0.15, v_PL∝ M^−0.5) against a matched no-kick control. The imposed mass dependence is recovered at injection, with the combined-channel median coupled kick decreasing from $10.716$ to 0.708 km s^−1 across five mass bins---a factor of ∼15.1. A mass-dependent trend remains visible after $100$~Myr of Galactic propagation in the matched kicked-versus-control displacement, whose median decreases from $0.7001$ to $0.0539$~kpc across the same bins. The remaining numerical distinction is concentrated in this mass-resolved differential displacement rather than in the bulk phase-space moments: the final velocity dispersions of the null and coupled kicked populations are nearly identical, only a few percent of particles leave the adopted disk region, and the fraction of particles satisfying the formal Galactic-unbound criterion (E_i>0) remains negligible in every diagnostic we report. Comparing each kicked population against its matched no-kick control shows that much of the overall kinematic heating arises from the evolution of the initially warm, nonequilibrium disk rather than from the ejection kick itself, isolating the kick's smaller contribution.
ER -